Isoform-specific Stimulation of Cardiac Na/K Pumps by Nanomolar Concentrations of Glycosides

Journal of General Physiology - Tập 119 Số 4 - Trang 297-312 - 2002
Junyuan Gao1,2, Randy S. Wymore3, Yongli Wang1,2, Glenn R. Gaudette2,4, Irvin B. Krukenkamp2,4, Ira S. Cohen1,2, Richard T. Mathias1,2
11Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY 11794-8661
22Institute of Molecular Cardiology, State University of New York at Stony Brook, Stony Brook, NY 11794-8661
34Department of Biology, The University of Tulsa, Tulsa, OK 74104-3189
43Department of Surgery, Health Sciences Center, State University of New York at Stony Brook, Stony Brook, NY 11794-8661

Tóm tắt

It is well-known that micromolar to millimolar concentrations of cardiac glycosides inhibit Na/K pump activity, however, some early reports suggested nanomolar concentrations of these glycosides stimulate activity. These early reports were based on indirect measurements in multicellular preparations, hence, there was some uncertainty whether ion accumulation/depletion rather than pump stimulation caused the observations. Here, we utilize the whole-cell patch-clamp technique on isolated cardiac myocytes to directly measure Na/K pump current (IP) in conditions that minimize the possibility of ion accumulation/depletion causing the observed effects. In guinea pig ventricular myocytes, nanomolar concentrations of dihydro-ouabain (DHO) caused an outward current that appeared to be due to stimulation of IP because of the following: (1) it was absent in 0 mM [K+]o, as was IP; (2) it was absent in 0 mM [Na+]i, as was IP; (3) at reduced [Na+]i, the outward current was reduced in proportion to the reduction in IP; (4) it was eliminated by intracellular vanadate, as was IP. Our previous work suggested guinea pig ventricular myocytes coexpress the α1- and α2-isoforms of the Na/K pumps. The stimulation of IP appears to be through stimulation of the high glycoside affinity α2-isoform and not the α1-isoform because of the following: (1) regulatory signals that specifically increased activity of the α2-isoform increased the amplitude of the stimulation; (2) regulatory signals that specifically altered the activity of the α1-isoform did not affect the stimulation; (3) changes in [K+]o that affected activity of the α1-isoform, but not the α2-isoform, did not affect the stimulation; (4) myocytes from one group of guinea pigs expressed the α1-isoform but not the α2-isoform, and these myocytes did not show the stimulation. At 10 nM DHO, total IP increased by 35 ± 10% (mean ± SD, n = 18). If one accepts the hypothesis that this increase is due to stimulation of just the α2-isoform, then activity of the α2-isoform increased by 107 ± 30%. In the guinea pig myocytes, nanomolar ouabain as well as DHO stimulated the α2-isoform, but both the stimulatory and inhibitory concentrations of ouabain were ∼10-fold lower than those for DHO. Stimulation of IP by nanomolar DHO was observed in canine atrial and ventricular myocytes, which express the α1- and α3-isoforms of the Na/K pumps, suggesting the other high glycoside affinity isoform (the α3-isoform) also was stimulated by nanomolar concentrations of DHO. Human atrial and ventricular myocytes express all three isoforms, but isoform affinity for glycosides is too similar to separate their activity. Nevertheless, nanomolar DHO caused a stimulation of IP that was very similar to that seen in other species. Thus, in all species studied, nanomolar DHO caused stimulation of IP, and where the contributions of the high glycoside affinity α2- and α3-isoforms could be separated from that of the α1-isoform, it was only the high glycoside affinity isoform that was stimulated. These observations support early reports that nanomolar concentrations of glycosides stimulate Na/K pump activity, and suggest a novel mechanism of isoform-specific regulation of IP in heart by nanomolar concentrations of endogenous ouabain-like molecules.

Từ khóa


Tài liệu tham khảo

1979, Life Sci., 25, 1803, 10.1016/0024-3205(79)90427-2

1992, Basic Res. Cardiol., 87(Suppl.), 87

1989, Nature., 340, 718, 10.1038/340718a0

1991, Eur. J. Biochem., 196, 129, 10.1111/j.1432-1033.1991.tb15795.x

1940, Am. Heart J., 20, 556

1996, Mol. Cell. Biochem., 163-164, 277, 10.1007/BF00408668

1976, J. Physiol., 260, 75, 10.1113/jphysiol.1976.sp011505

1987, J. Physiol., 383, 251, 10.1113/jphysiol.1987.sp016407

2000, J. Biol. Chem., 275, 1976, 10.1074/jbc.275.3.1976

1994, Eur. Heart J., 15, 1184, 10.1093/oxfordjournals.eurheartj.a060651

1983, J. Cardiovasc. Pharmacol., 5, 309, 10.1097/00005344-198303000-00024

1992, J. Physiol., 449, 689, 10.1113/jphysiol.1992.sp019109

1995, J. Gen. Physiol., 106, 995, 10.1085/jgp.106.5.995

1999, J. Physiol., 516, 377, 10.1111/j.1469-7793.1999.0377v.x

1999, Biophys. J., 76, A85

1999, Pflügers Arch., 437, 643, 10.1007/s004240050828

1990, J. Membr. Biol., 115, 109, 10.1007/BF01869450

1977, Nature., 265, 165, 10.1038/265165a0

1979, Br. J. Pharmacol., 66, 175, 10.1111/j.1476-5381.1979.tb13662.x

1939, J. Pharmacol. Exp. Ther., 67, 50

1989, Science., 244, 983, 10.1126/science.2543073

1975, Arch. Int. Pharmacodyn. Ther., 213, 222

1981, J. Clin. Invest., 68, 1207, 10.1172/JCI110366

1982, Pflügers Arch., 395, 6, 10.1007/BF00584963

1997, Crit. Rev. Clin. Lab. Sci., 34, 225, 10.3109/10408369708998094

1997, Ann. NY Acad. Sci., 834, 634, 10.1111/j.1749-6632.1997.tb52335.x

1996, Mol. Cell. Biochem., 160, 111

1997, Mol. Cell. Biochem., 169, 85, 10.1023/A:1006851411650

1993, FEBS Lett., 330, 297, 10.1016/0014-5793(93)80892-X

1987, J. Biol. Chem., 262, 6842, 10.1016/S0021-9258(18)48321-4

2000, News Physiol. Sci., 15, 176

1989, Circ. Res., 64, 1063, 10.1161/01.RES.64.6.1063

1980, Cardiovasc. Res., 14, 495, 10.1093/cvr/14.9.495

1988, Biophys. J., 54, 791, 10.1016/S0006-3495(88)83017-0

1974, Eur. J. Pharmacol., 26, 115, 10.1016/0014-2999(74)90082-X

1991, Biochem. Biophys. Res. Commun., 179, 1434, 10.1016/0006-291X(91)91733-S

1993, Cardiovasc. Res., 27, 2229, 10.1093/cvr/27.12.2229

1989, Biochim. Biophys. Acta., 988, 185, 10.1016/0304-4157(89)90019-1

1980, Naunyn Schmiedebergs Arch. Pharmacol., 314, 161, 10.1007/BF00504533

1998, J. Physiol., 509, 117, 10.1111/j.1469-7793.1998.117bo.x

1999, J. Membr. Biol., 169, 39, 10.1007/PL00005899

1996, Basic Res. Cardiol., 91, 256, 10.1007/BF00788912

1993, Biochim. Biophys. Acta., 1149, 189, 10.1016/0005-2736(93)90200-J

Thông tin
Thông tin xuất bản

Journal of General Physiology

Tập 119 Số 4

297-312

Thông tin tác giả