Contraction Accelerates Myosin Heavy Chain Synthesis Rates in Adult Cardiocytes by an Increase in the Rate of Translational Initiation

The purpose of this study was to determine the mechanism by which contraction acutely accelerates the synthesis rate of the contractile protein myosin heavy chain (MHC). Laminin-adherent adult feline cardiocytes were maintained in a serum-free medium and induced to contract at 1 Hz via electrical field stimulation. Electrical stimulation of contraction accelerated rates of MHC synthesis 28%, p < 0.05 by 4 h as determined by incorporation of phenylalanine into MHC. MHC mRNA expression as measured by RNase protection was unchanged after 4 h of electrical stimulation. MHC mRNA levels in messenger ribonucleoprotein complexes and translating polysomes were examined by sucrose gradient fractionation. The relative percentage of polysome-bound MHC mRNA was equal at 47% in both electrically stimulated and control cardiocytes. However, electrical stimulation of contraction resulted in a reproducible shift of MHC mRNA from smaller polysomes into larger polysomes, indicating an increased rate of initiation. This shift resulted in significant increases in MHC mRNA levels in the fractions containing the larger polysomes of electrically stimulated cardiocytes as compared with nonstimulated controls. These data indicate that the rate of MHC synthesis is accelerated in contracting cardiocytes via an increase in translational efficiency. The purpose of this study was to determine the mechanism by which contraction acutely accelerates the synthesis rate of the contractile protein myosin heavy chain (MHC). Laminin-adherent adult feline cardiocytes were maintained in a serum-free medium and induced to contract at 1 Hz via electrical field stimulation. Electrical stimulation of contraction accelerated rates of MHC synthesis 28%, p < 0.05 by 4 h as determined by incorporation of phenylalanine into MHC. MHC mRNA expression as measured by RNase protection was unchanged after 4 h of electrical stimulation. MHC mRNA levels in messenger ribonucleoprotein complexes and translating polysomes were examined by sucrose gradient fractionation. The relative percentage of polysome-bound MHC mRNA was equal at 47% in both electrically stimulated and control cardiocytes. However, electrical stimulation of contraction resulted in a reproducible shift of MHC mRNA from smaller polysomes into larger polysomes, indicating an increased rate of initiation. This shift resulted in significant increases in MHC mRNA levels in the fractions containing the larger polysomes of electrically stimulated cardiocytes as compared with nonstimulated controls. These data indicate that the rate of MHC synthesis is accelerated in contracting cardiocytes via an increase in translational efficiency. INTRODUCTIONHypertrophic growth occurs in terminally differentiated adult cardiocytes by an increase in cellular mass via a relatively coordinate increase in the proteins comprising each of the cellular components (1Marino T.A. Kent R.L. Uboh C.E. Fernandez E. Thompson E.W. Cooper G. Am. J. Physiol. 1985; 249: H371-H379PubMed Google Scholar). This accumulation of cardiocyte proteins occurs by an increase in rates of protein synthesis relative to rates of protein degradation (2Morgan H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar). The anabolic changes that occur during hypertrophy of the adult myocardium are generally considered to be a compensatory response to an increase in hemodynamic load(3Cooper IV, G. Annu. Rev. Physiol. 1987; 49: 501-508Crossref PubMed Google Scholar). As demonstrated in studies employing isolated papillary muscle preparations, both the active tension and passive strain components of load have been identified as mechanical stimuli for accelerating protein synthesis rates in adult myocardium (4Peterson M.B. Lesch M. Circ. Res. 1972; 31: 317-327Crossref PubMed Scopus (66) Google Scholar, 5Kent R.L. Hoober J.K. Cooper IV, G. Circ. Res. 1989; 64: 74-85Crossref PubMed Scopus (130) Google Scholar). These have been to isolated adult cardiocytes in of protein synthesis were accelerated in response to electrically stimulated cardiocyte Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar, Cooper IV, G. McDermott P.J. Am. J. Physiol. Google in response to a load as by of the cardiocytes to the and of a IV, G. Hoober J.K. Gordon Kent R.L. T.A. Circ. Res. PubMed Scopus Google and in response to passive of cardiocytes to a Kent R.L. Cooper IV, G. Circ. Res. 1989; 64: PubMed Scopus Google Scholar). the of adult cardiocytes in is maintained with to the to changes in mechanical load into an anabolic response as accelerated protein synthesis by which cardiocyte protein synthesis is occur at and translational Am. J. Physiol. Google Scholar). is for that and mRNA levels and are for changes in expression during hypertrophy PubMed Scopus Google Scholar, PubMed Scopus Google Scholar). the translational protein synthesis rates be accelerated by changes in H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar, Am. J. Physiol. Google Scholar). to the with which the cardiocyte translational as and translational to the relative of translational components in the in the and synthesis rates are accelerated by an increased translational during growth of the H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar, H.E. Chua B.H.L. Res. 1985; Google Scholar, Chua B.H.L. H.E. Am. J. Physiol. 1985; PubMed Google Scholar). of the for changes in translational is in studies in which protein synthesis rates increased after a load was R.L. Hoober J.K. Cooper IV, G. Circ. Res. 1989; 64: 74-85Crossref PubMed Scopus (130) Google Scholar, Y. P.J. Gordon E.E. H.E. Am. J. Physiol. PubMed Google Scholar, McDermott P.J. Kent R.L. M. Cooper IV, G. Circ. Res. PubMed Scopus Google Scholar, Am. J. Physiol. Google Scholar). These studies that cardiocyte protein synthesis be by a in which changes in translational are by changes in translational in load have a translational in the PubMed Scopus Google Scholar, Am. J. Physiol. Google Scholar, Am. J. Physiol. 1989; Google Scholar). of the muscle in in a in MHC heavy synthesis which been to a in translational Am. J. Physiol. 1989; Google studies employing adult feline cardiocytes in demonstrated that electrically stimulated contraction resulted in an of both protein synthesis and MHC synthesis Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar). of that this via a mechanism an increase in translational protein synthesis rates were accelerated by was with the of electrical stimulation were by 1 the of protein synthesis changes in the of translational as by an increase in the this MHC was as a to determine translational are in the of the rate of protein synthesis in response to electrically stimulated contraction of adult cardiocytes. were cardiocytes and cardiocytes electrically stimulated to contract by the synthesis rate of MHC the of the MHC mRNA and the translational of MHC These studies demonstrated rates of MHC synthesis are accelerated by electrical stimulation a in mRNA and the mechanism for accelerating MHC synthesis in contracting cardiocytes is an increase in translational as by a shift of MHC mRNA into larger feline cardiocytes were by in with mechanical as Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar, IV, G. Hoober J.K. Gordon Kent R.L. T.A. Circ. Res. PubMed Scopus Google Scholar, Kent R.L. Cooper IV, G. Circ. Res. 1989; 64: PubMed Scopus Google Scholar). the cardiocytes were in serum-free medium with at a of The were with to an the medium was to The medium was as and adult feline which are in were induced to contract via electrical field stimulation as with Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar). to a larger of the was to the of Am. J. Physiol. PubMed Google for with in which electrical were to the medium via at the of each The was The of the was with each electrical to at the to the for the to of the was determined and by in an response of The of were as a for a of at 1 Hz for 4 of of MHC synthesis were determined by incorporation of into MHC. were with the 4 h of electrical stimulation. protein was in a and The were for and to The were gradient for h at The MHC was identified by and The was in to with The protein was by to a of and at The was with and by The was in by to for 1 were for by and for MHC protein by the as a The of in the medium was determined by of of studies have that the to of medium in both electrically stimulated and Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google for MHC were to MHC mRNA RNase protection were by in from a of the into a Res. 1989; PubMed Scopus Google Scholar). This of mRNA from of the and is as by a to mRNA and an to the of adult been demonstrated that the is Cooper IV, G. Am. J. Physiol. Google Scholar). to that the of of the was the for feline a for feline was isolated from an adult feline cardiocyte The of the as the was the of to the of the and mRNA of the that the of of feline to is the as for J. and J. RNase protection from adult cardiocytes a of the for the a of feline mRNA was that the feline was to mRNA in the and and to in the and The was into a were by the chain to the and of the of MHC mRNA cellular was from via the and MHC mRNA was by an RNase protection as The was in containing 1 were for of by as Kent R.L. McDermott P.J. Circ. Res. PubMed Scopus Google Scholar). was in and the were at was h at by of for h with of were with of The were and in with of as The were by in and in were for at and The were and for The MHC mRNA was by of and to the of as determined by of MHC mRNA in were with to which was to chain were from the in of by and in 1 of The were with of a and to a of a containing was and the was and for were at to and The of MHC mRNA was measured by RNase protection and polysomes for RNase protection were sucrose and for at in an were into fractions of with the by and as MHC mRNA levels in each were determined by the RNase protection as to were to by were for the by the sucrose and for at in an The were into fractions of each with the of the The were and The was in and at for The was by of a and The were at in a containing of and feline MHC in The were 1 h with at by 1 h at in The were for and the of the were measured by to the MHC to the of in the the were and to the The was for and measured by of were from electrically stimulated and as for of the was to for and a was of sucrose were h in a at and and were by gradient and and in were by the of and PubMed Google and in was as a percentage of Chua B.H.L. H.E. Am. J. Physiol. 1985; PubMed Google Scholar, PubMed Google was the of cardiocytes were from the nonstimulated and electrically stimulated were determined a of p < 0.05 was considered to be a significant have demonstrated that contraction induced by electrical stimulation accelerated rates of protein synthesis and rates of MHC the relatively of cardiocytes were for the of polysomes and The was to electrically of cardiocytes with the of to that the anabolic response as Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google was in cardiocytes this rates of MHC synthesis were measured 4 h of electrically stimulated contraction and compared with nonstimulated controls. with contraction acutely accelerated the rate of MHC synthesis as compared with nonstimulated of contraction MHC synthesis of MHC synthesis were determined after 4 h of in electrically stimulated and cardiocytes. significant p < 0.05 as determined by a are cardiocyte to determine the of MHC synthesis was to an increase in MHC mRNA MHC mRNA expression was an RNase protection for the RNase protection are is demonstrated that the from to feline the in adult feline cardiocytes. As and this the that the is from a that is and the of the feline for is the of the RNase protection is demonstrated by the of the MHC as a of the of feline cardiocyte to the These data the of the for changes in MHC mRNA levels in feline cardiocyte of for feline MHC the of the and the feline of from adult was of the RNase protection for MHC mRNA levels in adult feline cardiocytes. was from cardiocytes and to the in the The of the MHC the was measured by MHC mRNA levels were compared electrically stimulated and nonstimulated in each of is an the MHC RNase to for the of that was and to the of each were and for The data of MHC mRNA to are in These data that electrically stimulated contraction MHC mRNA in the MHC as that in was the of a of from the cardiocytes. was a in MHC levels in this for the of to the the of MHC synthesis measured after 4 h of electrical stimulation significant changes in MHC mRNA mRNA in and electrically stimulated cardiocytes. a of an RNase protection for MHC. in stimulated and control from was data of of the in were to in each was significant the as determined by a are the cardiocyte rates of MHC synthesis were accelerated a in MHC examined the MHC mRNA was for protein synthesis in electrically stimulated cardiocytes. to determine the relative of the MHC mRNA active in the of MHC mRNA that was in the fractions and in the fractions of the from were sucrose and The were into a containing and and and a containing polysomes to in As demonstrated in the of MHC mRNA in the and polysome-bound fractions were the in electrically stimulated and nonstimulated cardiocytes. data from are in that equal of MHC mRNA were in the translating of the in both electrically stimulated and nonstimulated cardiocytes. The were MHC mRNA levels were to the of MHC synthesis was for by a significant of MHC mRNA into of electrically stimulated contraction the of MHC mRNA in a of cardiocytes the of the gradient gradient fractions of each were as by and the at was a of an RNase protection for MHC mRNA in the gradient fractions from electrically stimulated and nonstimulated cardiocytes. data of RNase protection for MHC mRNA in The were into as in the The percentage of MHC mRNA in the gradient fractions each of was by the percentage of in each of the significant p < as determined by a are cardiocyte mRNA in and polysome-bound cardiocyte a of an RNase protection for MHC mRNA in the fractions sucrose gradient fractionation. The of MHC mRNA in each was determined by the RNase protection The relative of MHC mRNA in each was as a percentage of MHC were significant in MHC mRNA in the fractions as determined by The were MHC mRNA was to are 4 cardiocyte the relative of the MHC mRNA in polysomes was unchanged in electrically stimulated the of MHC mRNA in the translating polysomes was were sucrose as and the into fractions with the is a gradient the of the and the of each of an RNase protection which demonstrated that in nonstimulated the of MHC mRNA was to the were smaller in fractions 4 the of the gradient that the larger electrical stimulation of contraction resulted in a shift of MHC mRNA into gradient fractions 4 and to larger data are for the RNase protection to MHC mRNA in the gradient as that in as a the were into the and the and and the be that was of the gradient fractions 1 and and of the containing polysomes gradient fractions and MHC mRNA was in gradient The percentage of MHC mRNA in the gradient fractions each of was from the of MHC mRNA in the gradient to for in the the were by the of in each of the gradient as determined from data were for preparations, of the and in of the for data in that MHC mRNA relative to was in the of the gradient containing smaller polysomes to in both nonstimulated and electrically stimulated cardiocytes. was a of MHC mRNA in the containing the and with the data in the containing larger polysomes polysomes and MHC mRNA to the of increased from 0.05 to in electrically stimulated a significant increase of the in MHC mRNA in the and fractions of electrically stimulated cardiocytes were the of for the increase of in the heavy a shift of MHC mRNA from the of the gradient resulted in a relatively increase of MHC mRNA in the larger fractions of electrically stimulated of and polysomes was for by to a were significant in the percentage of in each of the gradient electrically stimulated and nonstimulated gradient fractions to the by the RNase protection the were and MHC mRNA levels in the gradient fractions were measured by a feline The of the is demonstrated in the the from each gradient was the the of in each was measured by the and to the These from the RNase protection in that the were at a to the of the of the and the in the larger the of MHC mRNA in of nonstimulated and electrically stimulated cardiocytes are The percentage of MHC mRNA in each gradient was from the of MHC mRNA in the gradient The were by the percentage of in each for in of and to the in fractions and to the and fractions 4 to the and fractions and to the nonstimulated MHC mRNA relative to was in fractions 4 and and in the fractions containing the larger was MHC mRNA relative to in of electrically stimulated cardiocytes. MHC mRNA in this increased from in nonstimulated to in electrically stimulated cardiocytes. of was the data that was a reproducible shift of MHC mRNA from the smaller polysomes into the larger polysomes in of electrically stimulated cardiocytes. These data are with the in that of MHC mRNA from the smaller fractions in increases in MHC mRNA in the larger polysomes of electrically stimulated cardiocytes. the of MHC mRNA in of electrically stimulated to increased p < nonstimulated 4 of electrically stimulated contraction the of MHC mRNA in fractions of each were by with the of the and the at was MHC mRNA was measured by a feline The were and for The percentage of MHC mRNA in each gradient was and for by by the percentage of in each of in the of electrically stimulated and cardiocytes. The relative of was as a percentage of the of significant p < as determined by a are 4 cardiocyte is demonstrated that the changes in the of MHC mRNA in the of electrically stimulated cardiocytes were to of and each the relative of was as a percentage of the of were significant in the of the of and electrically stimulated cardiocytes. were significant in of in the gradient fractions of electrically stimulated and nonstimulated cardiocytes increase in translational have resulted from an increase in translational in which were into to this the percentage of to and was The percentage of in the of the gradient was in electrically stimulated and in nonstimulated cardiocytes. to the MHC mRNA electrical stimulation a significant of the into the in adult is a relatively increase in cardiocyte protein that the terminally differentiated is T.A. Kent R.L. Uboh C.E. Fernandez E. Thompson E.W. Cooper G. Am. J. Physiol. 1985; 249: H371-H379PubMed Google Scholar). The synthesis of proteins as and myosin are increased in to accumulation of protein and into J. J. PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar). the electrical stimulation in this was accumulation of myosin protein the However, with adult of have demonstrated that electrical stimulation of adult feline cardiocytes increased protein and significant changes in and Cooper IV, G. McDermott P.J. Am. J. Physiol. Google Scholar). is in of hypertrophy that a in the synthesis of contractile changes in the expression of contractile protein in PubMed Scopus Google Scholar, Am. J. 1987; PubMed Scopus Google Scholar). However, in the of larger changes in expression occur to a for and occur for PubMed Scopus Google Scholar, Cooper IV, G. Am. J. Physiol. Google Scholar, Am. J. 1987; PubMed Scopus Google Scholar). a changes in contractile protein synthesis rates in response to load to mRNA levels in adult Am. J. Physiol. Google Scholar, J. PubMed Scopus Google Scholar). preparations, contractile resulted in a in MHC synthesis rate a in MHC mRNA Am. J. Physiol. Google Scholar). an load was via an of MHC synthesis rate was accelerated in a in MHC translational a in contractile protein synthesis rates in adult in the after a in MHC mRNA the that was of the and after 4 h of electrically stimulated contractile The in in the were in to an mRNA in adult feline cardiocyte the of that the was induced in adult feline cardiocytes the of a feline However, the that mRNA was induced is for the feline cardiocytes the and MHC expression in adult in response to Cooper IV, G. Am. J. Physiol. Google Scholar). expression in of cardiocytes mRNA in Am. J. Physiol. Google Scholar, Kent R.L. McDermott P.J. Circ. Res. PubMed Scopus Google Scholar, Am. J. Physiol. Google Scholar). contractile increased expression of the in of the in adult feline PubMed Scopus Google Scholar, Am. J. Physiol. Google Scholar). data from both and and that the and of the MHC by the RNase protection mRNA was induced by electrically stimulated changes were as the the as the The shift of MHC into larger polysomes was the the feline were for the of the in which was a of at the and of and and with equal that the MHC mRNA was of MHC synthesis in response to electrically stimulated contraction of a in MHC mRNA that the in synthesis rate were to translational efficiency. are to the of the MHC mRNA at the of chain initiation. The mechanism a of mRNA from to translating polysomes, the mechanism an increased rate of mRNA in the Annu. Rev. PubMed Scopus Google Scholar). The data in that MHC synthesis rates were accelerated by of MHC mRNA into polysomes, was a percentage of cellular MHC mRNA in the The for the relatively percentage of MHC mRNA with to is the percentage of MHC in in and 1987; 49: PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, J. Google Scholar). The adult cardiocytes were and maintained in a and were to the as cardiocytes in of adult feline cardiocytes in serum-free medium have a rate of protein synthesis as compared with maintained in medium with Circ. Res. PubMed Scopus Google Scholar). These rates an translational and in for the relatively percentage of MHC mRNA in the mechanism to increase translational is by the rate of of mRNA relative to the rate of chain in an increased of MHC mRNA Annu. Rev. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, PubMed Google Scholar). The data in are with this of mechanism as was MHC mRNA mass of in larger the was to for of polysomes from the gradient of in the gradient fractions was the nonstimulated and electrically stimulated the shift of MHC mRNA into polysomes of electrically stimulated cardiocytes is of the that are MHC mRNA relative to The is that the MHC mRNA be as are mRNA As an the shift of mRNA into polysomes have resulted from a in chain as occurs during with PubMed Scopus Google Scholar, PubMed Google Scholar). a in protein synthesis rate was the of a rate of chain Am. J. Physiol. PubMed Google Scholar). The of a rate is of chain be to a an in MHC synthesis is the increase in translational was for MHC The changes in MHC synthesis rate in contracting cardiocytes be of a increase in translational efficiency. studies demonstrated that rates of protein synthesis were acutely accelerated by electrical and MHC synthesis rates were accelerated to a Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar). was an increase in translational of protein a of the be to into the shift into larger This was the as the percentage of in the in electrically stimulated and were in the of in the larger fractions of electrically stimulated as compared with cardiocytes. However, an shift of into larger polysomes have of the relatively percentage of in the fractions in and in a terminally differentiated as the adult the synthesis of MHC increase in to protein the relative of MHC mRNA is maintained at a synthesis MHC mRNA an rate of initiation. relatively changes in MHC synthesis as measured in response to electrically stimulated contraction occur by the MHC for a of of of the translational components that are in accelerating protein Res. PubMed Scopus Google is generally that changes in translational the of translational that are for chain Annu. Rev. PubMed Scopus Google Scholar, Res. PubMed Scopus Google Scholar). the adult a translational mechanism for accelerating the rate of protein synthesis to coordinate protein synthesis and the differentiated during the of The studies that protein synthesis be accelerated to an increase in the indicating that was a translational mechanism for the of protein synthesis rates acutely be by an increase in translational a mechanism for accelerating protein synthesis during growth of the (2Morgan H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar). a for cardiocyte protein synthesis rates in response to a the of by a increase in the relative of translational INTRODUCTIONHypertrophic growth occurs in terminally differentiated adult cardiocytes by an increase in cellular mass via a relatively coordinate increase in the proteins comprising each of the cellular components (1Marino T.A. Kent R.L. Uboh C.E. Fernandez E. Thompson E.W. Cooper G. Am. J. Physiol. 1985; 249: H371-H379PubMed Google Scholar). This accumulation of cardiocyte proteins occurs by an increase in rates of protein synthesis relative to rates of protein degradation (2Morgan H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar). The anabolic changes that occur during hypertrophy of the adult myocardium are generally considered to be a compensatory response to an increase in hemodynamic load(3Cooper IV, G. Annu. Rev. Physiol. 1987; 49: 501-508Crossref PubMed Google Scholar). As demonstrated in studies employing isolated papillary muscle preparations, both the active tension and passive strain components of load have been identified as mechanical stimuli for accelerating protein synthesis rates in adult myocardium (4Peterson M.B. Lesch M. Circ. Res. 1972; 31: 317-327Crossref PubMed Scopus (66) Google Scholar, 5Kent R.L. Hoober J.K. Cooper IV, G. Circ. Res. 1989; 64: 74-85Crossref PubMed Scopus (130) Google Scholar). These have been to isolated adult cardiocytes in of protein synthesis were accelerated in response to electrically stimulated cardiocyte Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar, Cooper IV, G. McDermott P.J. Am. J. Physiol. Google in response to a load as by of the cardiocytes to the and of a IV, G. Hoober J.K. Gordon Kent R.L. T.A. Circ. Res. PubMed Scopus Google and in response to passive of cardiocytes to a Kent R.L. Cooper IV, G. Circ. Res. 1989; 64: PubMed Scopus Google Scholar). the of adult cardiocytes in is maintained with to the to changes in mechanical load into an anabolic response as accelerated protein synthesis by which cardiocyte protein synthesis is occur at and translational Am. J. Physiol. Google Scholar). is for that and mRNA levels and are for changes in expression during hypertrophy PubMed Scopus Google Scholar, PubMed Scopus Google Scholar). the translational protein synthesis rates be accelerated by changes in H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar, Am. J. Physiol. Google Scholar). to the with which the cardiocyte translational as and translational to the relative of translational components in the in the and synthesis rates are accelerated by an increased translational during growth of the H.E. Gordon E.E. Kira Y. Chua B.H.L. Russo L.A. Peterson C.J. McDermott P.J. Watson P.A. Annu. Rev. Physiol. 1987; 49: 533-543Crossref PubMed Google Scholar, H.E. Chua B.H.L. Res. 1985; Google Scholar, Chua B.H.L. H.E. Am. J. Physiol. 1985; PubMed Google Scholar). of the for changes in translational is in studies in which protein synthesis rates increased after a load was R.L. Hoober J.K. Cooper IV, G. Circ. Res. 1989; 64: 74-85Crossref PubMed Scopus (130) Google Scholar, Y. P.J. Gordon E.E. H.E. Am. J. Physiol. PubMed Google Scholar, McDermott P.J. Kent R.L. M. Cooper IV, G. Circ. Res. PubMed Scopus Google Scholar, Am. J. Physiol. Google Scholar). These studies that cardiocyte protein synthesis be by a in which changes in translational are by changes in translational in load have a translational in the PubMed Scopus Google Scholar, Am. J. Physiol. Google Scholar, Am. J. Physiol. 1989; Google Scholar). of the muscle in in a in MHC heavy synthesis which been to a in translational Am. J. Physiol. 1989; Google studies employing adult feline cardiocytes in demonstrated that electrically stimulated contraction resulted in an of both protein synthesis and MHC synthesis Kent R.L. Cooper IV, G. McDermott P.J. Am. J. Physiol. PubMed Google Scholar). of that this via a mechanism an increase in translational protein synthesis rates were accelerated by was with the of electrical stimulation were by 1 the of protein synthesis changes in the of translational as by an increase in the this MHC was as a to determine translational are in the of the rate of protein synthesis in response to electrically stimulated contraction of adult cardiocytes. were cardiocytes and cardiocytes electrically stimulated to contract by the synthesis rate of MHC the of the MHC mRNA and the translational of MHC These studies demonstrated rates of MHC synthesis are accelerated by electrical stimulation a in mRNA and the mechanism for accelerating MHC synthesis in contracting cardiocytes is an increase in translational as by a shift of MHC mRNA into larger