Collagen-induced human platelet activation relies on the influx of calcium via the reverse mode of the Na+/Ca2+ exchanger, driven by a thromboxane A2-mediated increase in intracellular sodium.
The mechanism of collagen-induced human platelet activation was examined using Ca2+, Na+, and the pH-sensitive fluorescent dyes calcium green/fura red, sodium-binding benzofuran isophthalate, and 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Administration of a moderate dose of collagen (10 μg/ml) to human platelets resulted in an increase in Ca2+i and platelet aggregation. The majority of this increase in Ca2+i resulted from the influx of calcium from the extracellular milieu via the Na+/Ca2+ exchanger (NCX) functioning in the reverse mode and was reduced in a dose-dependent manner by the NCX inhibitors 5-(4-chlorobenzyl)-2′,4′-dimethylbenzamil (KD50 = 4.7 ± 1.1 μm) and KB-R7943 (KD50 = 35.1 ± 4.8 μm). Collagen-induced platelet aggregation was dependent on an increase in Ca2+i and could be inhibited by chelation of intra- and extracellular calcium through the administration of 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM) and EGTA, respectively, or via the administration of BAPTA-AM to platelets suspended in no-Na+/HEPES buffer. Collagen induced an increase in Na+i (23.2 ± 7.6 mm) via the actions of thromboxane A2 and, to a lesser extent, of the Na+/H+ exchanger. This study demonstrates that the collagen-induced increase in Ca2+i is dependent on the concentration of Na+ in the extracellular milieu, indicating that the collagen-induced increase in Na+i causes the reversal of the NCX, ultimately resulting in an increase in Ca2+i and platelet aggregation. The mechanism of collagen-induced human platelet activation was examined using Ca2+, Na+, and the pH-sensitive fluorescent dyes calcium green/fura red, sodium-binding benzofuran isophthalate, and 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Administration of a moderate dose of collagen (10 μg/ml) to human platelets resulted in an increase in Ca2+i and platelet aggregation. The majority of this increase in Ca2+i resulted from the influx of calcium from the extracellular milieu via the Na+/Ca2+ exchanger (NCX) functioning in the reverse mode and was reduced in a dose-dependent manner by the NCX inhibitors 5-(4-chlorobenzyl)-2′,4′-dimethylbenzamil (KD50 = 4.7 ± 1.1 μm) and KB-R7943 (KD50 = 35.1 ± 4.8 μm). Collagen-induced platelet aggregation was dependent on an increase in Ca2+i and could be inhibited by chelation of intra- and extracellular calcium through the administration of 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM) and EGTA, respectively, or via the administration of BAPTA-AM to platelets suspended in no-Na+/HEPES buffer. Collagen induced an increase in Na+i (23.2 ± 7.6 mm) via the actions of thromboxane A2 and, to a lesser extent, of the Na+/H+ exchanger. This study demonstrates that the collagen-induced increase in Ca2+i is dependent on the concentration of Na+ in the extracellular milieu, indicating that the collagen-induced increase in Na+i causes the reversal of the NCX, ultimately resulting in an increase in Ca2+i and platelet aggregation. Collagen is the most thrombogenic component of the subendothelium (1Baumgartner H.R. Haudenschild C. Ann. N. Y. Acad. Sci. 1972; 201: 22-36Crossref PubMed Scopus (162) Google Scholar). Following vascular damage, collagen is exposed to circulating platelets and both acts as a substrate for the adhesion of platelets (2Cowan D.H. Robertson A.L. Shook P. Giroski P. Br. J. Haematol. 1981; 47: 257-267Crossref PubMed Scopus (25) Google Scholar, 3Morton L.F. Peachey A.R. Barnes M.J. Biochem. J. 1989; 258: 157-163Crossref PubMed Scopus (72) Google Scholar, 4Poole A.W. Watson S.P. Br. J. Pharmacol. 1995; 115: 101-106Crossref PubMed Scopus (53) Google Scholar) and induces platelet activation (4Poole A.W. Watson S.P. Br. J. Pharmacol. 1995; 115: 101-106Crossref PubMed Scopus (53) Google Scholar). The prevailing evidence proposes that two receptors are involved in the platelet response to collagen; integrin α2β1 acts to adhere platelets to collagen, allowing platelets to interact with the lower affinity receptor glycoprotein VI, which is mainly responsible for platelet activation (3Morton L.F. Peachey A.R. Barnes M.J. Biochem. J. 1989; 258: 157-163Crossref PubMed Scopus (72) Google Scholar, 5Santoro S.A. Walsh J.J. Staatz W.D. Baranski K.J. Cell Regul. 1991; 2: 905-913Crossref PubMed Scopus (93) Google Scholar). Many of the platelet responses to collagen progress simultaneously when platelets adhere to collagen. At high concentrations, collagen activation of platelets has been shown to proceed through activation of phospholipase Cγ2 and subsequent cleavage of phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and 1,2-diacylglycerol (6Rittenhouse S.E. Allen C.L. J. Clin. Investig. 1982; 70: 1216-1224Crossref PubMed Scopus (53) Google Scholar, 7Watson S.P. Reep B. McConnell R.T. Lapetina E.G. Biochem. J. 1985; 226: 831-837Crossref PubMed Scopus (88) Google Scholar). Inositol 1,4,5-trisphosphate induces the release of calcium from the dense tubular system (8Authi K.S. Crawford N. Biochem. J. 1985; 230: 247-253Crossref PubMed Scopus (71) Google Scholar, 9Brass L.F. Joseph S.K. J. Biol. Chem. 1985; 260: 15172-15179Abstract Full Text PDF PubMed Google Scholar), whereas 1,2-diacylglycerol activates protein kinase C (10Nishizuka Y. Nature. 1984; 308: 693-698Crossref PubMed Scopus (5766) Google Scholar). The collagen-induced inositol 1,4,5-trisphosphate-mediated increase in Ca2+i is accompanied by an influx of calcium from the extracellular milieu (11Ardlie N.G. Garrett J.J. Bell L.K. Thromb. Res. 1986; 42: 115-124Abstract Full Text PDF PubMed Scopus (26) Google Scholar, 12Roberts D.E. Bose R. Ann. N. Y. Acad. Sci. 2002; 976: 345-349Crossref PubMed Scopus (12) Google Scholar). 1,2-Diacylglycerol and calcium mediate the characteristic platelet activation responses such as shape change, granule secretion, and aggregation. At lower concentrations, many of the effects of collagen are enhanced by its production of thromboxane A2 (TXA) 1The abbreviations used are: TXA, thromboxane A2; NCX, Na+/Ca2+ exchanger; NHE, Na+/H+ exchanger; BAPTA-AM, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetrakis(acetoxymethyl ester); CBDMB, 5-(4-chlorobenzyl)-2′,4′-dimethylbenzamil; EIPA, 5-(N-ethyl-N-isopropyl)amiloride. (6Rittenhouse S.E. Allen C.L. J. Clin. Investig. 1982; 70: 1216-1224Crossref PubMed Scopus (53) Google Scholar, 13Pollock W.K. Rink T.J. Irvine R.F. Biochem. J. 1986; 235: 869-877Crossref PubMed Scopus (218) Google Scholar, 14McNicol A. Nickolaychuk B.R. Biochem. Pharmacol. 1995; 50: 1795-1802Crossref PubMed Scopus (14) Google Scholar, 15Nakano T. Terawaki A. Arita H. J. Biochem. (Tokyo). 1986; 99: 1285-1288Crossref PubMed Scopus (20) Google Scholar). The collagen-induced increase in Ca2+i can be decreased by inhibiting the production of TXA via the pretreatment of platelets with cyclooxygenase inhibitors such as aspirin (11Ardlie N.G. Garrett J.J. Bell L.K. Thromb. Res. 1986; 42: 115-124Abstract Full Text PDF PubMed Scopus (26) Google Scholar, 16Feijge M.A. van Pampus E.C. Lacabaratz-Porret C. Hamulyak K. Levy-Toledano S. Enouf J. Heemskerk J.W. Br. J. Haematol. 1998; 102: 850-859Crossref PubMed Scopus (32) Google Scholar, 17Shiraishi M. Ikeda M. Fujishiro T. Fukuyama K. Ito K. Cell Calcium. 2000; 27: 53-60Crossref PubMed Scopus (10) Google Scholar). Calcium is an important second messenger in the platelet activation cascade. At rest, a Ca2+i of ∼100 nm is maintained by a balance between the leak of Ca2+ into the platelet and the concurrent efflux of free Ca2+ across the plasma membrane of the platelet and accumulation in intracellular stores (18Rink T.J. Smith S.W. Tsien R.Y. FEBS Lett. 1982; 148: 21-26Crossref PubMed Scopus (387) Google Scholar, 19Purdon A.D. Daniel J.L. Stewart G.J. Holmsen H. Biochim. Biophys. Acta. 1984; 800: 178-187Crossref PubMed Scopus (16) Google Scholar). Ca2+ is moved out across the plasma membrane through the actions of the plasma membrane Ca2+-ATPase and the Na+/Ca2+ exchanger (NCX). Plasma membrane Ca2+-ATPases are membrane-inserted enzymes that use the energy of ATP hydrolysis to move Ca2+ against its gradient and across the membrane. The NCX is capable of moving Ca2+ into or out of the platelet cytosol in exchange for Na+ (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, 21Schaeffer J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar). In the resting state, the NCX removes Ca2+ from the platelet cytosol. Internally, Ca2+ is transported into the dense tubular system by the sarco/endoplasmic reticulum Ca2+-ATPases 2b and 3 (22Papp B. Enyedi A. Kovacs T. Sarkadi B. Wuytack F. Thastrup O. Gardos G. Bredoux R. Levy-Toledano S. Enouf J. J. Biol. Chem. 1991; 266: 14593-14596Abstract Full Text PDF PubMed Google Scholar, 23Wuytack F. Papp B. Verboomen H. Raeymaekers L. Dode L. Bobe R. Enouf J. Bokkala S. Authi K.S. Casteels R. J. Biol. Chem. 1994; 269: 1410-1416Abstract Full Text PDF PubMed Google Scholar). In response to a moderate dose of collagen (10 μg/ml), ∼70% of the increase in Ca2+i is due to the influx of Ca2+ from the extracellular milieu, with the remainder as a function of Ca2+ release from the dense tubular system (12Roberts D.E. Bose R. Ann. N. Y. Acad. Sci. 2002; 976: 345-349Crossref PubMed Scopus (12) Google Scholar). Because voltage-gated calcium channels are not present in platelets Thromb. Haemostasis. 1985; PubMed Scopus Google Scholar, Rink T.J. Biochem. Biophys. Res. 1986; PubMed Scopus Google Scholar, Biochem. Biophys. Res. 1985; PubMed Scopus Google Scholar, Res. PubMed Scopus Google Scholar), a calcium or a reverse mode NCX could to the influx of Ca2+ (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, 21Schaeffer J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar, M.P. Rink T.J. J. Biol. Chem. Full Text PDF PubMed Google Scholar). The influx of Na+ be for the reversal of of Na+ has been shown activation of platelets by and J. Biol. Chem. 1984; Full Text PDF PubMed Google Scholar, H. M. B. Biochim. Biophys. Acta. PubMed Scopus Google Scholar, Feinberg H. Biochim. Biophys. Acta. PubMed Scopus Google Scholar). and S. J. PubMed Scopus Google Scholar) that a Ca2+i of nm and a membrane of membrane and in response to collagen D.E. Rink T.J. Thromb. Haemostasis. 1982; 47: PubMed Scopus Google a in Na+i can in the reversal of the Na+/H+ could to the increase in Na+i and subsequent NCX The of this study was to the mechanism responsible for the collagen-induced increase in human platelet that the majority of the collagen-induced increase in Ca2+i from the influx of Ca2+ from the extracellular milieu via the NCX functioning in the reverse The reverse mode NCX to be a of the influx of Na+ into the platelet cytosol via the actions of TXA and, to a lesser extent, of the was from aspirin for to into the The plasma was from by for from plasma by for in of plasma and with the fluorescent could not be used for the of Ca2+i due to with a of the for the of the NCX Bose R. Biochem. PubMed Scopus Google Scholar). In this two calcium (10 μm) and which are responses in used in Calcium and of or and are to with as from platelet shape change, and platelet the of two and the in of This of dyes has been used in many platelets M. M. S. S. A. PubMed Google Scholar). This was in a of shown in The of the free in platelets was to that in was component in the of the with free Ca2+i in The free calcium concentration was as S. K. J. Scopus Google Scholar) and into the of in the and the of the The of the for calcium from a of platelets as shown in The from platelet was ± The of the collagen-induced release of calcium from platelets with the calcium green/fura was to that with a used for calcium in platelets was with (10 and Na+i was with sodium-binding benzofuran μm). was for to the of the platelets from the plasma and extracellular by using a The platelets in and in a and to or was for to to Ca2+ was to the platelet a of the platelet was in aspirin for The was to the which in the of to a platelet concentration of shown that platelets for Smith M. J. Biol. Chem. 1985; 260: Full Text PDF PubMed Google Scholar, Smith M. J. Clin. Investig. 1986; PubMed Scopus Google Scholar, P. S. Bose R. J. Biol. 1991; Scholar, Y. Bose R. J. PubMed Google Scholar). platelets a Ca2+i and function with of platelets for to In platelets in and was a increase in Ca2+i and a in platelet function of platelets in on or on the collagen-induced in Ca2+i ± nm = not and ± = not with the ± = the of collagen (10 platelets in on the of this and of the platelets with Ca2+ for to the in and aggregation simultaneously in a The for Ca2+i was and the and The for and and the was Na+i the and and the was and Na+i to P. S. Bose R. J. Biol. 1991; Scholar, G. M. Tsien R.Y. J. Biol. Chem. 1985; 260: Full Text PDF PubMed Scopus Google Scholar). was as a in using a sodium-binding benzofuran and BAPTA-AM from and in was from J. and in KB-R7943 was from and in was from J. and in Collagen was from and in was from and in was from from are as ± the of from which platelets was and of was used for was as Calcium for Collagen-induced of collagen to human platelets suspended in Ca2+ resulted in a dose-dependent increase in Ca2+i (11Ardlie N.G. Garrett J.J. Bell L.K. Thromb. Res. 1986; 42: 115-124Abstract Full Text PDF PubMed Scopus (26) Google Scholar). The for the collagen-induced increase in Ca2+i the administration was ± = the of platelets suspended in with to activation with collagen (10 μg/ml) or with BAPTA-AM for and to activation with collagen (10 The chelation of extracellular calcium with decreased the collagen-induced in Ca2+i ± = and aggregation ± = In the of and EGTA, collagen induced a in Ca2+i ± = aggregation ± = with platelets that with BAPTA-AM and of and calcium in collagen activation of human collagen-induced in Ca2+i the administration of collagen (10 μg/ml) for platelet suspended in Ca2+ extracellular calcium by to the of collagen (10 μg/ml), or calcium through the of platelet with BAPTA-AM μm) and the administration of to the of collagen (10 in the collagen-induced platelet aggregation of platelet to the administration of collagen or with BAPTA-AM μm) and to the administration of collagen with platelet suspended in aggregation was the of collagen (10 collagen-induced in Ca2+i the administration of collagen to platelets suspended in Na+ and to platelets with BAPTA-AM and suspended in Na+ or Na+ in collagen-induced platelet aggregation the administration of collagen for platelet with BAPTA-AM and suspended in Na+ or Na+ with the = = of on the Collagen-induced in the effects of Na+ on the collagen-induced increase in platelets suspended in or and no-Na+/HEPES or to of extracellular Na+ resulted in a in both Ca2+i and aggregation of the used to that due to the of Na+ and not to the effects of or in a of the Na+ was using The collagen-induced in Ca2+i the of collagen was reduced by ± = for platelets suspended in buffer. suspended in or a collagen-induced in Ca2+i that was reduced by ± = and ± = that the in collagen-induced activation of human platelets in the of extracellular Na+ is due to the of Na+ and not to the used to of extracellular on the collagen-induced increase in Ca2+ and Na+ ± Na+, ± ± = Na+, ± ± = Na+, ± = ± = Na+, ± = ± = = = in a of intracellular calcium by in Ca2+ on the collagen-induced in Ca2+i ± = not reduced collagen-induced aggregation ± = In chelation of intracellular calcium in platelets suspended in reduced the collagen-induced increase in Ca2+i by ± nm = and the collagen-induced aggregation by ± = of the NCX by a in the collagen-induced increase in Ca2+i of ± nm = whereas of the by of the NCX a of ± = in collagen-induced platelet whereas of the by The NCX inhibitors and KB-R7943 decreased the collagen-induced in Ca2+i in a dose-dependent manner (12Roberts D.E. Bose R. Ann. N. Y. Acad. Sci. 2002; 976: 345-349Crossref PubMed Scopus (12) Google Scholar). The collagen activation 4.7 ± 1.1 for = and 35.1 ± 4.8 for KB-R7943 = Collagen-induced platelet activation was with an increase in of ± = from a of ± = with the NCX μm) not the collagen-induced in of the by μm) the collagen-induced increase in and decreased the by ± = with the Collagen-induced activation of platelets the by ± = which is not from with μm) or μm) not the collagen-induced in ± = not and ± = not with the for the Collagen-induced in and induced a increase in platelet which decreased a the collagen-induced Ca2+ release from the in Ca2+i which of the collagen-induced increase in Ca2+i is due to collagen-induced Ca2+ influx The collagen-induced release of intracellular Ca2+ was in the of platelet whereas the collagen-induced Ca2+ influx Na+i and to increase the the administration of collagen; the in In the in of in the Collagen-induced of and activation of human platelets resulted in an increase in Na+i of ± from a of ± of platelets with aspirin to the production of TXA reduced the collagen-induced increase in Na+i to 7.6 ± = pretreatment of platelets reduced the collagen-induced in Ca2+i from ± to ± nm = (11Ardlie N.G. Garrett J.J. Bell L.K. Thromb. Res. 1986; 42: 115-124Abstract Full Text PDF PubMed Scopus (26) Google Scholar, 17Shiraishi M. Ikeda M. Fujishiro T. Fukuyama K. Ito K. Cell Calcium. 2000; 27: 53-60Crossref PubMed Scopus (10) Google Scholar) and reduced aggregation by ± = (11Ardlie N.G. Garrett J.J. Bell L.K. Thromb. Res. 1986; 42: 115-124Abstract Full Text PDF PubMed Scopus (26) Google Scholar). The collagen-induced in Ca2+i in platelets was reduced by the administration of the NCX ± = or the ± = The collagen-induced aggregation of platelets was reduced by ± = by CBDMB, whereas not in a in collagen-induced aggregation ± = not of extracellular calcium with to collagen activation of platelets reduced the collagen-induced in Ca2+i to ± nm = of extracellular Ca2+ in platelet collagen-induced in Ca2+i 3 the administration of collagen to aspirin platelets suspended in or in by the administration of to collagen in Ca2+i 3 the administration of to platelets suspended in or in by the administration of to the administration of = = the TXA in platelet activation with collagen, the effects of a (10 μm) human platelets and Ca2+i which was by aspirin that ± = of the increase in Ca2+i was due to the influx of calcium from the extracellular milieu as by chelation of extracellular calcium with The increase in Ca2+i a to with collagen. reduced in Ca2+i from a of ± to ± nm = and aggregation by ± = reduced the in Ca2+i to ± = and reduced aggregation by ± = Collagen are exposed to circulating platelets to the and an important in through the of a the of vascular damage, (2Cowan D.H. Robertson A.L. Shook P. Giroski P. Br. J. Haematol. 1981; 47: 257-267Crossref PubMed Scopus (25) Google Scholar, 3Morton L.F. Peachey A.R. Barnes M.J. Biochem. J. 1989; 258: 157-163Crossref PubMed Scopus (72) Google Scholar, 4Poole A.W. Watson S.P. Br. J. Pharmacol. 1995; 115: 101-106Crossref PubMed Scopus (53) Google Scholar), and the of platelet platelets to the of as as the (4Poole A.W. Watson S.P. Br. J. Pharmacol. 1995; 115: 101-106Crossref PubMed Scopus (53) Google Scholar). The actions of collagen been in the for which that adhesion and activation of platelets are through the of collagen with platelet integrin α2β1 and glycoprotein VI, (3Morton L.F. Peachey A.R. Barnes M.J. Biochem. J. 1989; 258: 157-163Crossref PubMed Scopus (72) Google Scholar, 5Santoro S.A. Walsh J.J. Staatz W.D. Baranski K.J. Cell Regul. 1991; 2: 905-913Crossref PubMed Scopus (93) Google Scholar). Collagen-induced a activation is by shape change, granule secretion, and aggregation. responses are by an increase in Collagen induces a dose-dependent increase in Ca2+i N.G. Garrett J.J. Bell L.K. Thromb. Res. 1986; 42: 115-124Abstract Full Text PDF PubMed Scopus (26) Google and this of this increase in Ca2+i the collagen-induced aggregation of human an of the involved in calcium the of the collagen induces platelet aggregation. Collagen-induced in Ca2+i via the that the majority of the increase in Ca2+i in response to a moderate dose of collagen (10 μg/ml) is due to the influx of calcium from the extracellular milieu (12Roberts D.E. Bose R. Ann. N. Y. Acad. Sci. 2002; 976: 345-349Crossref PubMed Scopus (12) Google Scholar, Y. Bose R. J. PubMed Google Scholar). the NCX (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, 21Schaeffer J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar), and has been shown that the mode of of the NCX can be to an increase in Ca2+i (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, 21Schaeffer J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar, D.H. J. Biol. PubMed Scopus Google Scholar). This study has shown that the collagen-induced increase in Ca2+i is dependent on the concentration gradient of Na+ and that of the NCX the collagen-induced increase in that the Ca2+ influx in response to collagen is due to the actions of the NCX functioning in the reverse mode and from activation Bose R. Biochem. PubMed Scopus Google Scholar). Calcium influx through the NCX is dependent on the increase in Ca2+i when Na+ is is with the of the NCX functioning in the reverse mode (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, 21Schaeffer J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar, D.H. J. Biol. PubMed Scopus Google Scholar, L.F. J. Biol. Chem. 1984; Full Text PDF PubMed Google Scholar). the gradient on resting platelet indicating in the NCX is not functioning in a reverse collagen-induced activation of the platelets in a or resulted in a dose-dependent in the collagen-induced increase in with the increase in Ca2+i dependent on the gradient and resulting from the reversal of the This is in to the of on an increase in Ca2+i is due to of the NCX in the mode Y. Bose R. J. PubMed Google Scholar). The of extracellular Na+ in activation of human platelets is not to collagen. and reduced platelet activation in the of Na+ Acad. Sci. S. A. PubMed Scopus Google Scholar, J. Biol. Chem. 258: Full Text PDF PubMed Google Scholar). this is to the of Na+ as to an in the or of the Na+ was with or with or a in the collagen-induced in Ca2+i was with the of Na+, (12Roberts D.E. Bose R. Ann. N. Y. Acad. Sci. 2002; 976: 345-349Crossref PubMed Scopus (12) Google Scholar). can be that the effects are not due to or to the of the intracellular release of Ca2+ in response to collagen is in with the extracellular its be of intracellular calcium by not in a in the collagen-induced increase in a in collagen-induced aggregation. be the of the actions of in the or is that the collagen-induced influx of extracellular Ca2+ in a that was to an of the collagen-induced release of intracellular intracellular calcium chelation with a in extracellular a in the collagen-induced increase in Ca2+i and aggregation. In the protein kinase C μm) platelet aggregation that was by the chelation of intracellular calcium in the or of extracellular not The collagen-induced influx of Ca2+ through the reverse mode NCX is by the in both Ca2+i and aggregation through the administration of the NCX and a reverse NCX T. T. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), a dose-dependent of the collagen-induced in Collagen-induced in NCX mode of is dependent on the Na+ gradient (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, 21Schaeffer J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar, D.H. J. Biol. PubMed Scopus Google Scholar, L.F. J. Biol. Chem. 1984; Full Text PDF PubMed Google Scholar), and shown that the NCX reversal an increase in Na+i J. Blaustein M.P. Cell Calcium. 1989; 10: 101-113Crossref PubMed Scopus (82) Google Scholar, D.H. J. Biol. PubMed Scopus Google Scholar). that the collagen-induced reversal of NCX function be a of the in the platelet Na+ Because collagen-induced in Ca2+i when Na+ is maintained can be that NCX reversal is through a collagen-induced increase in Na+ influx has been in response to the platelet and J. Biol. Chem. 1984; Full Text PDF PubMed Google Scholar, H. M. B. Biochim. Biophys. Acta. PubMed Scopus Google Scholar) and collagen shown In the of and of the Na+ influx has been to activation of the inhibiting the has on the collagen-induced increase in Ca2+i or mechanism for the collagen-induced increase in The the exchange of extracellular Na+ for intracellular increase in subsequent to platelet activation calcium in response to platelet L.F. Joseph S.K. J. Biol. Chem. 1985; 260: 15172-15179Abstract Full Text PDF PubMed Google Scholar, A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar, J.W. Biochem. Sci. Full Text PDF PubMed Scopus Google Scholar). The present that collagen activation of platelets in an increase in by (20Rengasamy A. Soura S. Feinberg H. Thromb. Haemostasis. 1987; 57: 337-340Crossref PubMed Scopus (33) Google Scholar) that Ca2+ is enhanced high collagen of the platelet cytosol be mechanism that can increase Ca2+i platelet Collagen-induced of TXA the in Ca2+i and subsequent to platelet activation with collagen H. H. K. T. M. J. Biol. Chem. 1987; Full Text PDF PubMed Google Scholar), collagen-induced activation (6Rittenhouse S.E. Allen C.L. J. Clin. Investig. 1982; 70: 1216-1224Crossref PubMed Scopus (53) Google Scholar, 13Pollock W.K. Rink T.J. Irvine R.F. Biochem. J. 1986; 235: 869-877Crossref PubMed Scopus (218) Google Scholar, 14McNicol A. Nickolaychuk B.R. Biochem. Pharmacol. 1995; 50: 1795-1802Crossref PubMed Scopus (14) Google Scholar, 15Nakano T. Terawaki A. Arita H. J. Biochem. (Tokyo). 1986; 99: 1285-1288Crossref PubMed Scopus (20) Google Scholar). TXA production with aspirin reduced the collagen-induced increase in Ca2+i and aggregation and was by the chelation of extracellular platelets with aspirin decreased the collagen-induced increase in that TXA collagen activation of platelets through both of Ca2+ and influx of Na+ with of the Na+ The Ca2+ influx collagen activation of platelets was through the actions of the NCX functioning in the reverse mode as by the of NCX of the in platelets resulted in a in the collagen-induced in indicating that the a in the Na+ gradient for the reversal of the that the actions of the are not to are by the actions of The of the in platelet activation when TXA production is a for the NCX in platelet in the mode to calcium and the administration of collagen, a as an of platelet This is by the influx of via the actions of TXA and the as in evidence that collagen activation of human platelets an increase in the majority of which is due to the influx of Ca2+ through the NCX functioning in a reverse NCX reversal subsequent to the influx of Na+ due to the actions of TXA, and to a lesser by the TXA the actions of collagen.
Roberts et al. (Fri,) studied this question.