Abstract
The effects of changes in intracellular and extracellular free ionized [Mg2+] on inactivation of ICa and IBa in isolated ventricular myocytes of the frog were investigated using the whole-cell configuration of the patch-clamp technique. Intracellular [Mg2+] was varied by internal perfusion with solutions having different calculated free [Mg2+]. Increasing [Mg2+]i from 0.3 mM to 3.0 mM caused a 16% reduction in peak ICa amplitude and a 36% reduction in peak IBa amplitude, shifted the current-voltage relationship and the inactivation curve approximately 10 mV to the left, decreased relief from inactivation, and caused a dramatic increase in the rate of inactivation of IBa. The shifts in the current-voltage and inactivation curves were attributed to screening of internal surface charge by Mg2+. The increased rate of inactivation of IBa was due to an increase in both the steady-state level of inactivation as well as an increase in the rate of inactivation, as measured by two-pulse inactivation protocols. Increasing external [Mg2+] decreased IBa amplitude and shifted the current-voltage and inactivation curves to the right, but, in contrast to the effect of internal Mg2+, had little effect on the inactivation kinetics or the steady-state inactivation of IBa at potentials positive to 0 mV. These observations suggest that the Ca channel can be blocked quite rapidly by external Mg2+, whereas the block by [Mg2+]i is time and voltage dependent. We propose that inactivation of Ca channels can occur by both calcium-dependent and purely voltage-dependent mechanisms, and that a component of voltage-dependent inactivation can be modulated by changes in cytoplasmic Mg2+.
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- Akaike N., Tsuda Y., Oyama Y. Separation of current- and voltage-dependent inactivation of calcium current in frog sensory neuron. Neurosci Lett. 1988 Jan 11;84(1):46–50. doi: 10.1016/0304-3940(88)90335-7. [DOI] [PubMed] [Google Scholar]
- Alvarez-Leefmans F. J., Gamiño S. M., Giraldez F., González-Serratos H. Intracellular free magnesium in frog skeletal muscle fibres measured with ion-selective micro-electrodes. J Physiol. 1986 Sep;378:461–483. doi: 10.1113/jphysiol.1986.sp016230. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Argibay J. A., Fischmeister R., Hartzell H. C. Inactivation, reactivation and pacing dependence of calcium current in frog cardiocytes: correlation with current density. J Physiol. 1988 Jul;401:201–226. doi: 10.1113/jphysiol.1988.sp017158. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bean B. P. Two kinds of calcium channels in canine atrial cells. Differences in kinetics, selectivity, and pharmacology. J Gen Physiol. 1985 Jul;86(1):1–30. doi: 10.1085/jgp.86.1.1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bechem M., Pott L. Removal of Ca current inactivation in dialysed guinea-pig atrial cardioballs by Ca chelators. Pflugers Arch. 1985 May;404(1):10–20. doi: 10.1007/BF00581485. [DOI] [PubMed] [Google Scholar]
- Beeler G. W., Jr, Reuter H. Membrane calcium current in ventricular myocardial fibres. J Physiol. 1970 Mar;207(1):191–209. doi: 10.1113/jphysiol.1970.sp009056. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Brown A. M., Morimoto K., Tsuda Y., wilson D. L. Calcium current-dependent and voltage-dependent inactivation of calcium channels in Helix aspersa. J Physiol. 1981 Nov;320:193–218. doi: 10.1113/jphysiol.1981.sp013944. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Campbell D. L., Giles W. R., Hume J. R., Noble D., Shibata E. F. Reversal potential of the calcium current in bull-frog atrial myocytes. J Physiol. 1988 Sep;403:267–286. doi: 10.1113/jphysiol.1988.sp017249. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Cech S. Y., Broaddus W. C., Maguire M. E. Adenylate cyclase: the role of magnesium and other divalent cations. Mol Cell Biochem. 1980 Dec 10;33(1-2):67–92. doi: 10.1007/BF00224572. [DOI] [PubMed] [Google Scholar]
- Chad J. E., Eckert R. An enzymatic mechanism for calcium current inactivation in dialysed Helix neurones. J Physiol. 1986 Sep;378:31–51. doi: 10.1113/jphysiol.1986.sp016206. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chesnais J. M., Coraboeuf E., Sauviat M. P., Vassas J. M. Sensitivity to H, Li and Mg ions of the slow inward sodium current in frog atrial fibres. J Mol Cell Cardiol. 1975 Sep;7(9):627–642. doi: 10.1016/0022-2828(75)90140-6. [DOI] [PubMed] [Google Scholar]
- Cohen N. M., Lederer W. J. Calcium current in isolated neonatal rat ventricular myocytes. J Physiol. 1987 Oct;391:169–191. doi: 10.1113/jphysiol.1987.sp016732. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 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]
- Eckert R., Tillotson D. L. Calcium-mediated inactivation of the calcium conductance in caesium-loaded giant neurones of Aplysia californica. J Physiol. 1981 May;314:265–280. doi: 10.1113/jphysiol.1981.sp013706. [DOI] [PMC free article] [PubMed] [Google Scholar]
- FRANKENHAEUSER B., HODGKIN A. L. The action of calcium on the electrical properties of squid axons. J Physiol. 1957 Jul 11;137(2):218–244. doi: 10.1113/jphysiol.1957.sp005808. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fabiato A. Computer programs for calculating total from specified free or free from specified total ionic concentrations in aqueous solutions containing multiple metals and ligands. Methods Enzymol. 1988;157:378–417. doi: 10.1016/0076-6879(88)57093-3. [DOI] [PubMed] [Google Scholar]
- Fischmeister R., Hartzell H. C. Cyclic guanosine 3',5'-monophosphate regulates the calcium current in single cells from frog ventricle. J Physiol. 1987 Jun;387:453–472. doi: 10.1113/jphysiol.1987.sp016584. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fischmeister R., Hartzell H. C. Mechanism of action of acetylcholine on calcium current in single cells from frog ventricle. J Physiol. 1986 Jul;376:183–202. doi: 10.1113/jphysiol.1986.sp016148. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Flatman P. W. Magnesium transport across cell membranes. J Membr Biol. 1984;80(1):1–14. doi: 10.1007/BF01868686. [DOI] [PubMed] [Google Scholar]
- Godt R. E., Lindley B. D. Influence of temperature upon contractile activation and isometric force production in mechanically skinned muscle fibers of the frog. J Gen Physiol. 1982 Aug;80(2):279–297. doi: 10.1085/jgp.80.2.279. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gupta R. K., Benovic J. L., Rose Z. B. The determination of the free magnesium level in the human red blood cell by 31P NMR. J Biol Chem. 1978 Sep 10;253(17):6172–6176. [PubMed] [Google Scholar]
- Gupta R. K., Gupta P., Moore R. D. NMR studies of intracellular metal ions in intact cells and tissues. Annu Rev Biophys Bioeng. 1984;13:221–246. doi: 10.1146/annurev.bb.13.060184.001253. [DOI] [PubMed] [Google Scholar]
- Gupta R. K., Yushok W. D. Noninvasive 31P NMR probes of free Mg2+, MgATP, and MgADP in intact Ehrlich ascites tumor cells. Proc Natl Acad Sci U S A. 1980 May;77(5):2487–2491. doi: 10.1073/pnas.77.5.2487. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HODGKIN A. L., HUXLEY A. F. A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol. 1952 Aug;117(4):500–544. doi: 10.1113/jphysiol.1952.sp004764. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hadley R. W., Hume J. R. An intrinsic potential-dependent inactivation mechanism associated with calcium channels in guinea-pig myocytes. J Physiol. 1987 Aug;389:205–222. doi: 10.1113/jphysiol.1987.sp016654. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hamill O. P., Marty A., Neher E., Sakmann B., Sigworth F. J. Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch. 1981 Aug;391(2):85–100. doi: 10.1007/BF00656997. [DOI] [PubMed] [Google Scholar]
- Hartzell H. C., Fischmeister R. Effect of forskolin and acetylcholine on calcium current in single isolated cardiac myocytes. Mol Pharmacol. 1987 Nov;32(5):639–645. [PubMed] [Google Scholar]
- Hartzell H. C., Fischmeister R. Opposite effects of cyclic GMP and cyclic AMP on Ca2+ current in single heart cells. Nature. 1986 Sep 18;323(6085):273–275. doi: 10.1038/323273a0. [DOI] [PubMed] [Google Scholar]
- Hartzell H. C., Simmons M. A. Comparison of effects of acetylcholine on calcium and potassium currents in frog atrium and ventricle. J Physiol. 1987 Aug;389:411–422. doi: 10.1113/jphysiol.1987.sp016663. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Henquin J. C., Tamagawa T., Nenquin M., Cogneau M. Glucose modulates Mg2+ fluxes in pancreatic islet cells. Nature. 1983 Jan 6;301(5895):73–74. doi: 10.1038/301073a0. [DOI] [PubMed] [Google Scholar]
- Hess P., Metzger P., Weingart R. Free magnesium in sheep, ferret and frog striated muscle at rest measured with ion-selective micro-electrodes. J Physiol. 1982 Dec;333:173–188. doi: 10.1113/jphysiol.1982.sp014447. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kass R. S., Krafte D. S. Negative surface charge density near heart calcium channels. Relevance to block by dihydropyridines. J Gen Physiol. 1987 Apr;89(4):629–644. doi: 10.1085/jgp.89.4.629. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kass R. S., Sanguinetti M. C. Inactivation of calcium channel current in the calf cardiac Purkinje fiber. Evidence for voltage- and calcium-mediated mechanisms. J Gen Physiol. 1984 Nov;84(5):705–726. doi: 10.1085/jgp.84.5.705. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lansman J. B., Hess P., Tsien R. W. Blockade of current through single calcium channels by Cd2+, Mg2+, and Ca2+. Voltage and concentration dependence of calcium entry into the pore. J Gen Physiol. 1986 Sep;88(3):321–347. doi: 10.1085/jgp.88.3.321. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 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]
- Maughan D. Diffusible magnesium in frog skeletal muscle cells. Biophys J. 1983 Jul;43(1):75–80. doi: 10.1016/S0006-3495(83)84325-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mentrard D., Vassort G., Fischmeister R. Calcium-mediated inactivation of the calcium conductance in cesium-loaded frog heart cells. J Gen Physiol. 1984 Jan;83(1):105–131. doi: 10.1085/jgp.83.1.105. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mitra R., Morad M. Two types of calcium channels in guinea pig ventricular myocytes. Proc Natl Acad Sci U S A. 1986 Jul;83(14):5340–5344. doi: 10.1073/pnas.83.14.5340. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 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]
- Noma A., Kotake H., Irisawa H. Slow inward current and its role mediating the chronotropic effect of epinephrine in the rabbit sinoatrial node. Pflugers Arch. 1980 Oct;388(1):1–9. doi: 10.1007/BF00582621. [DOI] [PubMed] [Google Scholar]
- Reuter H. Calcium channel modulation by neurotransmitters, enzymes and drugs. Nature. 1983 Feb 17;301(5901):569–574. doi: 10.1038/301569a0. [DOI] [PubMed] [Google Scholar]
- Rosenberg R. L., Hess P., Tsien R. W. Cardiac calcium channels in planar lipid bilayers. L-type channels and calcium-permeable channels open at negative membrane potentials. J Gen Physiol. 1988 Jul;92(1):27–54. doi: 10.1085/jgp.92.1.27. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tillotson D. Inactivation of Ca conductance dependent on entry of Ca ions in molluscan neurons. Proc Natl Acad Sci U S A. 1979 Mar;76(3):1497–1500. doi: 10.1073/pnas.76.3.1497. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tsien R. W., Bean B. P., Hess P., Lansman J. B., Nilius B., Nowycky M. C. Mechanisms of calcium channel modulation by beta-adrenergic agents and dihydropyridine calcium agonists. J Mol Cell Cardiol. 1986 Jul;18(7):691–710. doi: 10.1016/s0022-2828(86)80941-5. [DOI] [PubMed] [Google Scholar]
- Tsien R. W. Calcium channels in excitable cell membranes. Annu Rev Physiol. 1983;45:341–358. doi: 10.1146/annurev.ph.45.030183.002013. [DOI] [PubMed] [Google Scholar]
- Tsien R. W. Cyclic AMP and contractile activity in heart. Adv Cyclic Nucleotide Res. 1977;8:363–420. [PubMed] [Google Scholar]
- Vassort G., Rougier O. Membrane potential and slow inward current dependence of frog cardiac mechanical activity. Pflugers Arch. 1972;331(3):191–203. doi: 10.1007/BF00589126. [DOI] [PubMed] [Google Scholar]
- Watanabe Y., Dreifus L. S. Electrophysiological effects of magnesium and its interactions with potassium. Cardiovasc Res. 1972 Jan;6(1):79–88. doi: 10.1093/cvr/6.1.79. [DOI] [PubMed] [Google Scholar]
- White R. E., Hartzell H. C. Effects of intracellular free magnesium on calcium current in isolated cardiac myocytes. Science. 1988 Feb 12;239(4841 Pt 1):778–780. doi: 10.1126/science.2448878. [DOI] [PubMed] [Google Scholar]
- White R. E., Hartzell H. C. Magnesium ions in cardiac function. Regulator of ion channels and second messengers. Biochem Pharmacol. 1989 Mar 15;38(6):859–867. doi: 10.1016/0006-2952(89)90272-4. [DOI] [PubMed] [Google Scholar]