Skip to main content
PMC home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1988 Dec;407:77–102. doi: 10.1113/jphysiol.1988.sp017404

Rapid regulation of the 'second inward current' by intracellular calcium in isolated rat and ferret ventricular myocytes.

M R Boyett 1, M S Kirby 1, C H Orchard 1
PMCID: PMC1191192  PMID: 2855743

Abstract

1. Single cells were isolated from the ventricles of ferret and rat hearts. Cells were voltage clamped using a single conventional microelectrode. Membrane voltage, membrane currents and cell length were monitored. 2. The current elicited by decreasing the membrane potential from a holding potential of -40 or -45 mV to potentials more positive than -20 mV was abolished by D600, by Cd2+ and by removal of Ca2+ from the cell superfusate. This current activated within 20 ms and inactivated over several hundred milliseconds; it had a bell-shaped current-voltage relation, and was maximal at about +10 mV. It is concluded that this is the fast Ca2+ current ICa. 3. Increasing bathing [Ca2+] (Ca2+o) led to the appearance of transient inward currents (Iti). If ICa was triggered during Iti, it was reduced in magnitude, and inactivated more slowly. 4. The sarcoplasmic reticulum inhibitor ryanodine (1 mumol/l) abolished Iti, and reduced twitch contraction, but had no direct effect on the magnitude of ICa, although its rate of inactivation was slowed. 5. Iti produced by depolarization of the holding potential, or by lowering bathing [K+] or [Na+], led to similar changes to those described in paragraph 3. 6. Gradually increasing diastolic cytoplasmic [Ca2+] (Ca2+i) by rapid stimulation in the presence of ryanodine, by lowering bathing [K+], or lowering bathing [Na+], led to a parallel decrease of ICa. 7. The effects of lowering bathing [Na+] could be abolished by using an electrode-filling solution containing EGTA. 8. In some ferret cells a slow component of the second inward current was observed. The size of this current was directly related to the size of the twitch: changes in the size of the twitch produced by changing the pattern of stimulation or application of ryanodine were paralleled by changes in the size of this current, but had no effect on the size of ICa. 9. It is concluded that the magnitude of ICa can be decreased by an increase of either resting Ca2+i, or the spontaneous increase of Ca2+ which underlies Iti, but it is not affected by the size of the stimulated calcium transient (although the time course of inactivation is dependent on the calcium transient). The size of the slow component of the second inward current, however, is directly related to the size of the twitch and may, therefore, be activated by Ca2+.

Full text

PDF

Images in this article

82Fig. 2
on p.82
89Fig. 9
on p.89
90Fig. 10
on p.90
95Fig. 14
on p.95

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Allen D. G., Eisner D. A., Orchard C. H. Factors influencing free intracellular calcium concentration in quiescent ferret ventricular muscle. J Physiol. 1984 May;350:615–630. doi: 10.1113/jphysiol.1984.sp015221. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Allen D. G., Eisner D. A., Pirolo J. S., Smith G. L. The relationship between intracellular calcium and contraction in calcium-overloaded ferret papillary muscles. J Physiol. 1985 Jul;364:169–182. doi: 10.1113/jphysiol.1985.sp015737. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Allen D. G., Kurihara S. Calcium transients in mammalian ventricular muscle. Eur Heart J. 1980;Suppl A:5–15. doi: 10.1093/eurheartj/1.suppl_1.5. [DOI] [PubMed] [Google Scholar]
  4. Bers D. M. Ca influx and sarcoplasmic reticulum Ca release in cardiac muscle activation during postrest recovery. Am J Physiol. 1985 Mar;248(3 Pt 2):H366–H381. doi: 10.1152/ajpheart.1985.248.3.H366. [DOI] [PubMed] [Google Scholar]
  5. Cannell M. B., Lederer W. J. A novel experimental chamber for single-cell voltage-clamp and patch-clamp applications with low electrical noise and excellent temperature and flow control. Pflugers Arch. 1986 May;406(5):536–539. doi: 10.1007/BF00583378. [DOI] [PubMed] [Google Scholar]
  6. Colquhoun D., Neher E., Reuter H., Stevens C. F. Inward current channels activated by intracellular Ca in cultured cardiac cells. Nature. 1981 Dec 24;294(5843):752–754. doi: 10.1038/294752a0. [DOI] [PubMed] [Google Scholar]
  7. Dow J. W., Harding N. G., Powell T. Isolated cardiac myocytes. I. Preparation of adult myocytes and their homology with the intact tissue. Cardiovasc Res. 1981 Sep;15(9):483–514. doi: 10.1093/cvr/15.9.483. [DOI] [PubMed] [Google Scholar]
  8. Eckert R., Chad J. E. Inactivation of Ca channels. Prog Biophys Mol Biol. 1984;44(3):215–267. doi: 10.1016/0079-6107(84)90009-9. [DOI] [PubMed] [Google Scholar]
  9. Eisner D. A., Lederer W. J., Vaughan-Jones R. D. The dependence of sodium pumping and tension on intracellular sodium activity in voltage-clamped sheep Purkinje fibres. J Physiol. 1981 Aug;317:163–187. doi: 10.1113/jphysiol.1981.sp013819. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Eisner D. A., Valdeolmillos M. A study of intracellular calcium oscillations in sheep cardiac Purkinje fibres measured at the single cell level. J Physiol. 1986 Mar;372:539–556. doi: 10.1113/jphysiol.1986.sp016024. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Eisner D. A., Valdeolmillos M. Measurement of intracellular calcium during the development and relaxation of tonic tension in sheep Purkinje fibres. J Physiol. 1986 Jun;375:269–281. doi: 10.1113/jphysiol.1986.sp016116. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Fabiato A. Simulated calcium current can both cause calcium loading in and trigger calcium release from the sarcoplasmic reticulum of a skinned canine cardiac Purkinje cell. J Gen Physiol. 1985 Feb;85(2):291–320. doi: 10.1085/jgp.85.2.291. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Fedida D., Noble D., Shimoni Y., Spindler A. J. Inward current related to contraction in guinea-pig ventricular myocytes. J Physiol. 1987 Apr;385:565–589. doi: 10.1113/jphysiol.1987.sp016508. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Hansford R. G., Lakatta E. G. Ryanodine releases calcium from sarcoplasmic reticulum in calcium-tolerant rat cardiac myocytes. J Physiol. 1987 Sep;390:453–467. doi: 10.1113/jphysiol.1987.sp016711. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Hilgemann D. W. Extracellular calcium transients and action potential configuration changes related to post-stimulatory potentiation in rabbit atrium. J Gen Physiol. 1986 May;87(5):675–706. doi: 10.1085/jgp.87.5.675. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Hume J. R. Component of whole cell Ca current due to electrogenic Na-Ca-exchange in cardiac myocytes. Am J Physiol. 1987 Mar;252(3 Pt 2):H666–H670. doi: 10.1152/ajpheart.1987.252.3.H666. [DOI] [PubMed] [Google Scholar]
  17. Lee K. S., Marban E., Tsien R. W. Inactivation of calcium channels in mammalian heart cells: joint dependence on membrane potential and intracellular calcium. J Physiol. 1985 Jul;364:395–411. doi: 10.1113/jphysiol.1985.sp015752. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. London B., Krueger J. W. Contraction in voltage-clamped, internally perfused single heart cells. J Gen Physiol. 1986 Oct;88(4):475–505. doi: 10.1085/jgp.88.4.475. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Marban E., Wier W. G. Ryanodine as a tool to determine the contributions of calcium entry and calcium release to the calcium transient and contraction of cardiac Purkinje fibers. Circ Res. 1985 Jan;56(1):133–138. doi: 10.1161/01.res.56.1.133. [DOI] [PubMed] [Google Scholar]
  20. Mitchell M. R., Powell T., Terrar D. A., Twist V. W. Calcium-activated inward current and contraction in rat and guinea-pig ventricular myocytes. J Physiol. 1987 Oct;391:545–560. doi: 10.1113/jphysiol.1987.sp016755. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Mitchell M. R., Powell T., Terrar D. A., Twist V. W. Characteristics of the second inward current in cells isolated from rat ventricular muscle. Proc R Soc Lond B Biol Sci. 1983 Oct 22;219(1217):447–469. doi: 10.1098/rspb.1983.0084. [DOI] [PubMed] [Google Scholar]
  22. Mitchell M. R., Powell T., Terrar D. A., Twist V. W. Influence of a change in stimulation rate on action potentials, currents and contractions in rat ventricular cells. J Physiol. 1985 Jul;364:113–130. doi: 10.1113/jphysiol.1985.sp015734. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Mitchell M. R., Powell T., Terrar D. A., Twist V. W. Ryanodine prolongs Ca-currents while suppressing contraction in rat ventricular muscle cells. Br J Pharmacol. 1984 Jan;81(1):13–15. doi: 10.1111/j.1476-5381.1984.tb10735.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Nilius B., Hess P., Lansman J. B., Tsien R. W. A novel type of cardiac calcium channel in ventricular cells. Nature. 1985 Aug 1;316(6027):443–446. doi: 10.1038/316443a0. [DOI] [PubMed] [Google Scholar]
  25. Noble D. The surprising heart: a review of recent progress in cardiac electrophysiology. J Physiol. 1984 Aug;353:1–50. doi: 10.1113/jphysiol.1984.sp015320. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Plant T. D., Standen N. B., Ward T. A. The effects of injection of calcium ions and calcium chelators on calcium channel inactivation in Helix neurones. J Physiol. 1983 Jan;334:189–212. doi: 10.1113/jphysiol.1983.sp014489. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Sheu S. S., Fozzard H. A. Transmembrane Na+ and Ca2+ electrochemical gradients in cardiac muscle and their relationship to force development. J Gen Physiol. 1982 Sep;80(3):325–351. doi: 10.1085/jgp.80.3.325. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Yue D. T., Marban E., Wier W. G. Relationship between force and intracellular [Ca2+] in tetanized mammalian heart muscle. J Gen Physiol. 1986 Feb;87(2):223–242. doi: 10.1085/jgp.87.2.223. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from The Journal of Physiology are provided here courtesy of The Physiological Society

RESOURCES