Diversity and Developmental Expression of L-type Calcium Channel β2 Proteins and Their Influence on Calcium Current in Murine Heart

By now, little is known on L-type calcium channel (LTCC) subunits expressed in mouse heart. We show that CaVβ2 proteins are the major CaVβ components of the LTCC in embryonic and adult mouse heart, but that in embryonic heart CaVβ3 proteins are also detectable. At least two CaVβ2 variants of ∼68 and ∼72 kDa are expressed. To identify the underlying CaVβ2 variants, cDNA libraries were constructed from poly(A)+ RNA isolated from hearts of 7-day-old and adult mice. Screening identified 60 independent CaVβ2 cDNA clones coding for four types of CaVβ2 proteins only differing in their 5′ sequences. CaVβ2-N1, -N4, and -N5 but not -N3 were identified in isolated cardiomyocytes by RT-PCR and were sufficient to reconstitute the CaVβ2 protein pattern in vitro. Significant L-type Ca2+ currents (ICa) were recorded in HEK293 cells after co-expression of CaV1.2 and CaVβ2. Current kinetics were determined by the type of CaVβ2 protein, with the ∼72-kDa CaVβ2a-N1 shifting the activation of ICa significantly to depolarizing potentials compared with the other CaVβ2 variants. Inactivation of ICa was accelerated by CaVβ2a-N1 and -N4, which also lead to slower activation compared with CaVβ2a-N3 and -N5. In summary, this study reveals the molecular LTCC composition in mouse heart and indicates that expression of various CaVβ2 proteins may be used to adapt the properties of LTCCs to changing myocardial requirements during development and that CaVβ2a-N1-induced changes of ICa kinetics might be essential in embryonic heart. By now, little is known on L-type calcium channel (LTCC) subunits expressed in mouse heart. We show that CaVβ2 proteins are the major CaVβ components of the LTCC in embryonic and adult mouse heart, but that in embryonic heart CaVβ3 proteins are also detectable. At least two CaVβ2 variants of ∼68 and ∼72 kDa are expressed. To identify the underlying CaVβ2 variants, cDNA libraries were constructed from poly(A)+ RNA isolated from hearts of 7-day-old and adult mice. Screening identified 60 independent CaVβ2 cDNA clones coding for four types of CaVβ2 proteins only differing in their 5′ sequences. CaVβ2-N1, -N4, and -N5 but not -N3 were identified in isolated cardiomyocytes by RT-PCR and were sufficient to reconstitute the CaVβ2 protein pattern in vitro. Significant L-type Ca2+ currents (ICa) were recorded in HEK293 cells after co-expression of CaV1.2 and CaVβ2. Current kinetics were determined by the type of CaVβ2 protein, with the ∼72-kDa CaVβ2a-N1 shifting the activation of ICa significantly to depolarizing potentials compared with the other CaVβ2 variants. Inactivation of ICa was accelerated by CaVβ2a-N1 and -N4, which also lead to slower activation compared with CaVβ2a-N3 and -N5. In summary, this study reveals the molecular LTCC composition in mouse heart and indicates that expression of various CaVβ2 proteins may be used to adapt the properties of LTCCs to changing myocardial requirements during development and that CaVβ2a-N1-induced changes of ICa kinetics might be essential in embryonic heart. Cardiac contractions require Ca2+ influx in cardiomyocytes from the extracellular fluid, which leads to Ca2+ release from the sarcoplasmic reticulum via ryanodine receptors (1Reuter H. Nature. 1983; 301: 569-574Crossref PubMed Scopus (862) Google Scholar). This Ca2+-induced Ca2+ release (CICR) 4The abbreviations used are: CICRCa2+-induced Ca2+ releaseCaVvoltage-dependent Ca2+ channelLTCCL-type calcium channelSH3Src homologyNKnucleotide kinaseVvariable regionCconstant regionEembryonic dayPpostnatal dayGSPgene-specific primer. causes a marked increase in intracellular Ca2+ concentration for short periods of time and underlies cardiac contraction (2Bers D.M. Nature. 2002; 415: 198-205Crossref PubMed Scopus (3352) Google Scholar, 3Fabiato A. Fabiato F. Annu. Rev. Physiol. 1979; 41: 473-484Crossref PubMed Scopus (300) Google Scholar). The Ca2+ influx into cardiac myocytes is mediated by high voltage-activated L-type Ca2+ channels (LTCCs), which are heteromultimeric complexes comprised predominantly of the pore-forming CaVα1 subunit and the auxiliary CaVβ subunit (4Catterall W.A. Annu. Rev. Cell Dev. Biol. 2000; 16: 521-555Crossref PubMed Scopus (1952) Google Scholar). In heart, the principal CaVα1 subunit, CaVα1c (CaV1.2), is encoded by the Cacna1C gene (5Mikami A. Imoto K. Tanabe T. Niidome T. Mori Y. Takeshima H. Narumiya S. Numa S. Nature. 1989; 340: 230-233Crossref PubMed Scopus (767) Google Scholar). Four genes (Cacnb1-4) encoding CaVβ subunits have been identified that are expressed in the heart of different species including human, rabbit, and rat (6Groner F. Rubio M. Schulte-Euler P. Matthes J. Khan I.F. Bodi I. Koch S.E. Schwartz A. Herzig S. Biochem. Biophys. Res. Commun. 2004; 314: 878-884Crossref PubMed Scopus (14) Google Scholar, 7Hullin R. Singer-Lahat D. Freichel M. Biel M. Dascal N. Hofmann F. Flockerzi V. EMBO J. 1992; 11: 885-890Crossref PubMed Scopus (280) Google Scholar, 8Haase H. Pfitzmaier B. McEnery M.W. Morano I. J. Cell. Biochem. 2000; 76: 695-703Crossref PubMed Scopus (35) Google Scholar). Ca2+-induced Ca2+ release voltage-dependent Ca2+ channel L-type calcium channel Src homology nucleotide kinase variable region constant region embryonic day postnatal day gene-specific primer. CaVβ proteins are ∼500 amino acid cytoplasmic proteins that bind to the CaVα1 I-II intracellular loop (9Pragnell M. De Waard M. Mori Y. Tanabe T. Snutch T.P. Campbell K.P. Nature. 1994; 368: 67-70Crossref PubMed Scopus (552) Google Scholar) and affect channel gating properties (4Catterall W.A. Annu. Rev. Cell Dev. Biol. 2000; 16: 521-555Crossref PubMed Scopus (1952) Google Scholar), trafficking (10Bichet D. Cornet V. Geib S. Carlier E. Volsen S. Hoshi T. Mori Y. De Waard M. Neuron. 2000; 25: 177-190Abstract Full Text Full Text PDF PubMed Scopus (313) Google Scholar, 11Altier C. Dubel S.J. Barrère C. Jarvis S.E. Stotz S.C. Spaetgens R.L. Scott J.D. Cornet V. De Waard M. Zamponi G.W. Nargeot J. Bourinet E. J. Biol. Chem. 2002; 277: 33598-33603Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar), regulation by neurotransmitter receptors through G-protein βγ subunit activation (12Dolphin A.C. Pharmacol. Rev. 2003; 55: 607-627Crossref PubMed Scopus (238) Google Scholar), and sensitivity to drugs (13Mitterdorfer J. Froschmayr M. Grabner M. Striessnig J. Glossmann H. FEBS Lett. 1994; 352: 141-145Crossref PubMed Scopus (55) Google Scholar). The CaVβ primary sequence encodes five domains, arranged V1-C1-V2-C2-V3. V1, V2, and V3 are variable domains, whereas C1 and C2 are conserved (14Walker D. De Waard M. Trends Neurosci. 1998; 21: 148-154Abstract Full Text Full Text PDF PubMed Scopus (314) Google Scholar). Structural studies reveal that C1 and C2 form a SH3 domain (Src homology 3 domain) and a NK domain (nucleotide kinase domain), respectively (15Hanlon M.R. Berrow N.S. Dolphin A.C. Wallace B.A. FEBS Lett. 1999; 445: 366-370Crossref PubMed Scopus (109) Google Scholar). Although C1-V2-C2 makes the CaVβ core, in heart the V1 region appears critical for the kinetics of ICa and heart function. Accordingly a mutation in the V1 region of the Cacnb2 gene was recently identified as an underlying cause of Brugada syndrome (16Cordeiro J.M. Marieb M. Pfeiffer R. Calloe K. Burashnikov E. Antzelevitch C. J. Mol. Cell Cardiol. 2009; 46: 695-703Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar). In mice-targeted deletion of the Cacnb2 gene (17Weissgerber P. Held B. Bloch W. Kaestner L. Chien K.R. Fleischmann B.K. Lipp P. Flockerzi V. Freichel M. Circ. Res. 2006; 99: 749-757Crossref PubMed Scopus (85) Google Scholar) but not of Cacnb1 (18Gregg R.G. Messing A. Strube C. Beurg M. Moss R. Behan M. Sukhareva M. Haynes S. Powell J.A. Coronado R. Powers P.A. Proc. Natl. Acad. Sci. U.S.A. 1996; 93: 13961-13966Crossref PubMed Scopus (200) Google Scholar), Cacnb3 (19Murakami M. Yamamura H. Suzuki T. Kang M.G. Ohya S. Murakami A. Miyoshi I. Sasano H. Muraki K. Hano T. Kasai N. Nakayama S. Campbell K.P. Flockerzi V. Imaizumi Y. Yanagisawa T. Iijima T. J. Biol. Chem. 2003; 278: 43261-43267Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, 20Namkung Y. Smith S.M. Lee S.B. Skrypnyk N.V. H. Proc. Natl. Acad. Sci. U.S.A. 1998; PubMed Scopus Google Scholar), J.M. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar) leads to a and heart, which causes of and and embryonic the Cacnb2 gene was in a cardiac (17Weissgerber P. Held B. Bloch W. Kaestner L. Chien K.R. Fleischmann B.K. Lipp P. Flockerzi V. Freichel M. Circ. Res. 2006; 99: 749-757Crossref PubMed Scopus (85) Google Scholar). Although to an essential of CaVβ2 for ICa and cardiac the of various CaVβ2 variants and of the expressed CaVβ2 proteins require studies on the subunit composition of LTCCs in the mouse heart. In and in of the of studies mouse Ca2+ channel subunits as in heart the of the gene underlying the mouse cardiac L-type channel is mouse I. Y. Mol. Cell. 2006; Full Text PDF PubMed Scopus Google Scholar, H. D.M. J. R. J.D. Circ. Res. PubMed Scopus Google Scholar, N. Nakayama H. H. S. H. R. J. L. J.D. Circ. Res. PubMed Scopus Google Scholar) a rat CaVβ2 E. A. P. E. L. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar) expressed in rat and N. D. R. E. L. Proc. Natl. Acad. Sci. U.S.A. 1998; PubMed Scopus Google Scholar), but not in heart N. D. R. E. L. Proc. Natl. Acad. Sci. U.S.A. 1998; PubMed Scopus Google Scholar), have only this been that the mouse of this is expressed in the mouse heart. five CaVβ2 variants only in the V1 domain have been identified from different species E. A. P. E. L. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, E. R.L. Mol. Pharmacol. Google Scholar, 1998; PubMed Scopus Google Scholar) and in heart variants have been by RT-PCR J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar, E. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). In is little on the CaVβ proteins in mouse heart, their variants, and expression We to study CaVβ expression in the heart and cDNA and to reveal their on LTCCs by the CaV1.2 protein were with and to and The was after with and CaVα1c and and and and which were and were used in this of was by protein from type and in and The CaV1.2 were by of heart poly(A)+ RNA was in and for were on and and were of and The RNA was on a to by and to the were for 3 in and The was with in four with the was to RNA was isolated from day heart was with of poly(A)+ RNA from adult mouse heart a CaVβ2 gene and the with for cDNA and cDNA libraries were constructed in and into were on clones were with cDNA the conserved C1 and C2 of CaVβ2 C2 3 of was for and 60 for gene-specific and and with the with of to and to were to for and clones were isolated and and adult cardiomyocytes were isolated as (17Weissgerber P. Held B. Bloch W. Kaestner L. Chien K.R. Fleischmann B.K. Lipp P. Flockerzi V. Freichel M. Circ. Res. 2006; 99: 749-757Crossref PubMed Scopus (85) Google Scholar, L. Lipp P. Proc. of Scopus Google Scholar). used the RT-PCR with cardiomyocytes were by in and used for and and the were were in the of of the used as in the of of were in for for to the and to for for and for HEK293 cells and cells were in and with and cells were with of CaVβ2 HEK293 cells were with CaV1.2 subunit with of the different cardiac CaVβ2 cDNA encoding and was with in cells were after Ca2+ HEK293 cells CaV1.2 and CaVβ2 were in a were with a and from to were and a ICa was to were from the of by from to in for to In HEK293 cells with CaV1.2 and a but ICa be ICa only cells with CaV1.2 and of the CaVβ2 with a were in the to that proteins CaV1.2 and CaVβ2 were from cells were with Dolphin A.C. PubMed Scopus Google Scholar), the the the for activation of the and the The time to was after the of the to The activation was constructed by the and to that and with a with as the of the was by a cells were from a of to potentials from to for in the to for was were to the after the to and with a with as the of and the were and currents recorded with an by the was used in to and were compared in a of We of for and to the CaVβ subunits in protein from adult mouse heart and by The and proteins are in adult of protein but not in the adult heart of cardiac proteins were In the CaVβ2 protein is in of protein and in heart of cardiac protein was that CaVβ2 is the CaVβ protein in the adult mouse heart. Accordingly of the Cacnb2 gene of and are in poly(A)+ RNA isolated from adult mouse heart The CaVβ2 protein is in the heart embryonic day To study expression during cardiac with protein from hearts from to and adult mouse hearts were for and the CaVα1c subunit In embryonic heart, a ∼72-kDa CaVβ2 protein is expressed the CaVβ2 protein in molecular with this embryonic ∼72-kDa CaVβ2 protein In of embryonic development a CaVβ2 protein of ∼68 kDa is whereas in the adult heart only the CaVβ2 protein and but not the ∼72-kDa protein is detectable. The CaVβ3 protein, which is expressed in and is to a in the protein from embryonic heart but not in adult heart and whereas the expression of the CaVα1c proteins CaVβ2 protein expression during cardiac development different CaVβ2 proteins are expressed during cardiac development to changes in LTCC protein The CaVβ3 protein is expressed in and but also in heart embryonic show expression of CaVβ3 in heart from type and but not in of hearts from CaVα1c and CaVβ2 subunits are the of embryonic and adult cardiac LTCC The molecular of the different CaVβ2 proteins by is not known but be by the expression of variants of the Cacnb2 which been in human, rabbit, and rat heart R. Singer-Lahat D. Freichel M. Biel M. Dascal N. Hofmann F. Flockerzi V. EMBO J. 1992; 11: 885-890Crossref PubMed Scopus (280) Google Scholar, J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar, B. D. S. V. E. J. Physiol. 2002; PubMed Scopus Google Scholar). In the identified and CaVβ2 variants in mouse heart by the of and of cDNA The Cacnb2 gene is on protein coding and a region of The 5′ and to the Cacnb2 gene by J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google for V1 and are the 5′ of the gene The are encoded by the and of CaVβ2 V3 region have been of V1 and be for the CaVβ2 protein pattern in To of CaVβ2 V1 and variants expressed in heart used the RNA was isolated from hearts from adult and from in the the and ∼72-kDa CaVβ2 proteins are We used and two types of for of cDNA To the nucleotide of the V1 and for which were the cDNA was by to the of the C2 and cDNA was by a the C1 constructed a cDNA the poly(A)+ RNA from which was with the encoding the C1 and the C2 The identify CaVβ2 variants with differing V3 60 independent cDNA clones were isolated from the libraries and The of clones encoded the of the V1 and of CaVβ2 and The clones also the C2 and V3 The domain was encoded in clones by and to the of J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar), clones are of the type for the were only the V1 domain which to of type and of the 60 clones encoded the that this is the in hearts from adult and 7-day-old mice. The clones of and CaVβ2a-N1 variants clones of are expressed to an The CaVβ2a-N3 was only the 60 CaVβ2 cDNA clones that this is only in a of cardiac LTCCs The is encoded by and the human, and rat amino acid of this are and with The 3 and in the of the rat protein have been identified as of E. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). cDNA was identified the is the mouse Cacnb2 an of the amino acid from the four types of clones only in the and whereas the with the amino acid are the four CaVβ2 variants. The V1 which in the rat have been to be in the heart in and in and in CaVβ2a-N3 Chien 1999; PubMed Scopus Google the expression of predominantly and in heart. of the cDNA poly(A)+ RNA been isolated from the RNA from and was To the expression cardiomyocytes from adult and embryonic hearts were to cDNA and for and of the that the CaVβ2-N1, -N4, and -N5 variants are expressed in adult and embryonic cardiomyocytes was for that is not expressed in cardiomyocytes the by cDNA that and are expressed in cardiac proteins are sufficient to the CaVβ2 protein pattern in the proteins were expressed in cells and of cells were used for used protein from hearts of adult and of The of and proteins expressed in cells the of the CaVβ2 protein expressed in the adult heart and in the heart In the CaVβ2a-N1 protein slower the ∼72-kDa CaVβ2 protein with the CaVβ2 protein in the heart. the and are the CaVβ2 proteins expressed in the adult mouse heart, whereas in hearts the CaVβ2a-N1 protein is This is by the that the protein of of the the pattern in In summary, CaVβ2 protein variants are expressed in mouse heart with CaVβ2a-N1 expressed predominantly in embryonic by the expression of and which and the CaVβ2 proteins in the heart. to study the of CaVβ2 proteins on LTCC currents To the expression as to the Ca2+ channel as to only the of the CaV1.2 and the CaVβ2 variants in HEK293 cardiac CaV1.2 cDNA was CaV1.2 cDNA from mouse heart and The and are to the of the cardiac and CaV1.2 proteins in (5Mikami A. Imoto K. Tanabe T. Niidome T. Mori Y. Takeshima H. Narumiya S. Numa S. Nature. 1989; 340: 230-233Crossref PubMed Scopus (767) Google Scholar, M. P. E. R. W. Flockerzi V. Hofmann F. FEBS Lett. PubMed Scopus Google Scholar), and on the of the CaV1.2 clones were to as and different potentials in HEK293 cells and of the CaVβ2 variants. used HEK293 cells and HEK293 cells Ca2+ currents were recorded in to of to to in from a of a of in the for the different are in in HEK293 cells and a CaVβ2 protein reveal which were not in HEK293 The ICa was in the of to that is the is potentials to is a in with currents from cells CaVβ2a-N1 were with a to the ICa properties for in the potentials and in the were the currents from cells and CaVβ2a-N1 to -N5 was in the of to was in the of to whereas the for was significantly different for cells with CaVβ2a-N1 activation and been to be by the type of CaVβ subunit in expression studies S. Biophys. J. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, J. Physiol. 1998; PubMed Scopus Google Scholar). in was a of CaVβ2a-N1 compared with -N4, and -N5 on the The of of the was to potentials by CaVβ2a-N1 compared with the -N4, and -N5 with and and The for was to be different and -N3 were the CaVβ2 variants on of ICa as be by the of the ICa for the various Inactivation kinetics of ICa were in the of CaVβ2a-N1 in the of CaVβ2a-N3 ICa from and channels with the CaVβ2a-N1 and as as CaVβ2a-N3 and two which kinetics to This is also the ICa after a from to and currents from only in the from to from channels a in the from to but in a of and In for currents from and channels the with from to from to from to a of for channels for -N5 Inactivation of ICa kinetics and the time of the the CaVβ2a-N3 lead to slower of ICa CaVβ2a-N1 The time for from other a was in the of of ICa a and the time significantly CaVβ2a-N1 to slower activation and CaVβ2a-N3 channel activation kinetics with for CaVβ2a-N1 and as as for CaVβ2a-N3 and the time to of ICa were for currents recorded from and channels for -N5 respectively In a of show that CaVβ2 is the major CaVβ protein expressed in the adult mouse heart and that a of CaVβ2 protein expression during studies of Ca2+ channel subunits and Ca2+ channel composition in the human, and rat heart (5Mikami A. Imoto K. Tanabe T. Niidome T. Mori Y. Takeshima H. Narumiya S. Numa S. Nature. 1989; 340: 230-233Crossref PubMed Scopus (767) Google Scholar, 7Hullin R. Singer-Lahat D. Freichel M. Biel M. Dascal N. Hofmann F. Flockerzi V. EMBO J. 1992; 11: 885-890Crossref PubMed Scopus (280) Google Scholar, E. A. P. E. L. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar, S. D. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, S. S. A. A. M. J. Biochem. 1999; PubMed Scopus Google Scholar, P. D. S. J. Biophys. PubMed Scopus Google Scholar) the molecular of the mouse cardiac LTCC is mouse have been with Ca2+ channel subunit as for heart I. Y. Mol. Cell. 2006; Full Text PDF PubMed Scopus Google Scholar, H. D.M. J. R. J.D. Circ. Res. PubMed Scopus Google Scholar, N. Nakayama H. H. S. H. R. J. L. J.D. Circ. Res. PubMed Scopus Google Scholar, R. Matthes J. S. Bodi I. Rubio M. K. Khan I. D. P. E. R. M. L. Schwartz A. Herzig S. PubMed Scopus Google Scholar, H. W. H. Schwartz A. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). In the mouse heart, LTCCs are (17Weissgerber P. Held B. Bloch W. Kaestner L. Chien K.R. Fleischmann B.K. Lipp P. Flockerzi V. Freichel M. Circ. Res. 2006; 99: 749-757Crossref PubMed Scopus (85) Google Scholar). expression of the CaVβ2 protein embryonic development whereas and protein expression was not detectable. The CaVβ3 protein is expressed in the embryonic hearts but not in hearts from and adult mice. We a in CaVβ2 protein expression from a ∼72-kDa protein, expressed embryonic to a protein in hearts from adult mice. To identify CaVβ2 variants constructed cDNA libraries which were by the conserved C1 and C2 which with the CaVβ2 J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar, E. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Biophys. J. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Khan I.F. D. Matthes J. A. D. Schwartz A. R. J. 21: PubMed Scopus Google Scholar) used the of a to CaVβ2 variants, which is determined by the used for In the of cDNA libraries a to identify which is expressed. In this makes to study the of a sufficient of clones are In the of cardiac independent cDNA clones were and an of the types of CaVβ2 variants expressed in mouse heart and their By this only CaVβ2 variants the C1-V2-C2 region E. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar) may have been We the by of the CaVβ2 variants identified by cDNA isolated cardiomyocytes as The identified CaVβ2 variants expressed in -N4, and which only in their V1 encoded by of the protein pattern of and proteins in by co-expression of -N4, and -N5 the protein pattern in protein from mouse heart different CaVβ2a-N1 is predominantly expressed in hearts from embryonic and whereas and -N5 are expressed in hearts from and adult mice. The CaVβ2a-N1 protein is not in protein from adult heart. from cDNA a of CaVβ2 protein in the adult heart, which might have with The the was not identified encodes a amino acid sequence which is to be to the protein coding the have been identified in rat cardiac 7Hullin R. Singer-Lahat D. Freichel M. Biel M. Dascal N. Hofmann F. Flockerzi V. EMBO J. 1992; 11: 885-890Crossref PubMed Scopus (280) Google Scholar) and heart J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar). The was identified clones but to be in with to be expressed in heart R. Singer-Lahat D. Freichel M. Biel M. Dascal N. Hofmann F. Flockerzi V. EMBO J. 1992; 11: 885-890Crossref PubMed Scopus (280) Google Scholar, N. D. R. E. L. Proc. Natl. Acad. Sci. U.S.A. 1998; PubMed Scopus Google Scholar) to independent in rat cardiomyocytes B. D. S. V. E. J. Physiol. 2002; PubMed Scopus Google Scholar). In studies the of CaVβ2 proteins on ICa was by channel subunits from different species J.D. McEnery M.W. Physiol. 2004; PubMed Scopus Google Scholar, S. Biophys. J. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Khan I.F. D. Matthes J. A. D. Schwartz A. R. J. 21: PubMed Scopus Google Scholar). to reconstitute a LTCC channel in a expression and with the CaVβ2 proteins identified The subunit is known to predominantly affect LTCC by CaV1.2 channel A. J. J. L. Dolphin A.C. Trends Pharmacol. Sci. Full Text Full Text PDF PubMed Scopus Google was not is not known which of the four genes is expressed in cardiac myocytes J. W. L. J. Biol. PubMed Scopus Google Scholar). The four variants -N4, and -N5 ICa in a with the Inactivation kinetics was accelerated in the of CaVβ2a-N1 and compared with the in the of CaVβ2a-N3 and -N5. slower ICa activation kinetics to with variants as as to the that the four variants form two S. Biophys. J. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). the two variants, CaVβ2a-N1 and which lead to are the predominantly expressed variants in embryonic and adult mouse heart. and channels show kinetics but in of activation and mouse heart an increase of heart is with potentials the adult the S.J. Smith J.M. J. Physiol. 1994; Google Scholar). The of the is in by the of of in a compared with with the from CaVβ2a-N1 to -N4, is for the properties during heart the of channels compared with CaVβ2a-N1 is the in embryonic heart and the may that in embryonic cardiac contraction intracellular Ca2+ Ca2+ influx via L-type Ca2+ channels S. Fleischmann B.K. H. J. Proc. Natl. Acad. Sci. U.S.A. 1999; PubMed Scopus Google Scholar). may also in with a and of L-type Ca2+ as in the of the of CaVβ2a-N1 but not in the of S. Khan I.F. D. Matthes J. A. D. Schwartz A. R. J. 21: PubMed Scopus Google Scholar). embryonic and not CaV1.2 to be the predominantly expressed H. K. T. N. M. A. Lee H. K. Y. I. Circ. J. PubMed Scopus Google Scholar), that with CaVβ2a-N1 in a different We and for for for and for and Lipp and for the adult isolated with