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. 2000 Dec;79(6):3052–3062. doi: 10.1016/S0006-3495(00)76540-4

Mg(2+) block unmasks Ca(2+)/Ba(2+) selectivity of alpha1G T-type calcium channels.

J R Serrano 1, S R Dashti 1, E Perez-Reyes 1, S W Jones 1
PMCID: PMC1301182  PMID: 11106611

Abstract

We have examined permeation by Ca(2+) and Ba(2+), and block by Mg(2+), using whole-cell recordings from alpha1G T-type calcium channels stably expressed in HEK 293 cells. Without Mg(o)(2+), inward currents were comparable with Ca(2+) and Ba(2+). Surprisingly, three other results indicate that alpha1G is actually selective for Ca(2+) over Ba(2+). 1) Mg(2+) block is approximately 7-fold more potent with Ba(2+) than with Ca(2+). With near-physiological (1 mM) Mg(o)(2+), inward currents were approximately 3-fold larger with 2 mM Ca(2+) than with 2 mM Ba(2+). The stronger competition between Ca(2+) and Mg(2+) implies that Ca(2+) binds more tightly than Ba(2+). 2) Outward currents (carried by Na(+)) are blocked more strongly by Ca(2+) than by Ba(2+). 3) The reversal potential is more positive with Ca(2+) than with Ba(2+), thus P(Ca) > P(Ba). We conclude that alpha1G can distinguish Ca(2+) from Ba(2+), despite the similar inward currents in the absence of Mg(o)(2+). Our results can be explained by a 2-site, 3-barrier model if Ca(2+) enters the pore 2-fold more easily than Ba(2+) but exits the pore at a 2-fold lower rate.

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Selected References

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  1. Almers W., McCleskey E. W. Non-selective conductance in calcium channels of frog muscle: calcium selectivity in a single-file pore. J Physiol. 1984 Aug;353:585–608. doi: 10.1113/jphysiol.1984.sp015352. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Andersen O. S. Graphic representation of the results of kinetic analyses. J Gen Physiol. 1999 Oct;114(4):589–590. doi: 10.1085/jgp.114.4.589. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. 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]
  4. Becchetti A., Arcangeli A., Del Bene M. R., Olivotto M., Wanke E. Intra and extracellular surface charges near Ca2+ channels in neurons and neuroblastoma cells. Biophys J. 1992 Oct;63(4):954–965. doi: 10.1016/S0006-3495(92)81665-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Bourinet E., Zamponi G. W., Stea A., Soong T. W., Lewis B. A., Jones L. P., Yue D. T., Snutch T. P. The alpha 1E calcium channel exhibits permeation properties similar to low-voltage-activated calcium channels. J Neurosci. 1996 Aug 15;16(16):4983–4993. doi: 10.1523/JNEUROSCI.16-16-04983.1996. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Brooks S. P., Storey K. B. Bound and determined: a computer program for making buffers of defined ion concentrations. Anal Biochem. 1992 Feb 14;201(1):119–126. doi: 10.1016/0003-2697(92)90183-8. [DOI] [PubMed] [Google Scholar]
  7. Campbell D. L., Giles W. R., Shibata E. F. Ion transfer characteristics of the calcium current in bull-frog atrial myocytes. J Physiol. 1988 Sep;403:239–266. doi: 10.1113/jphysiol.1988.sp017248. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Carbone E., Lux H. D., Carabelli V., Aicardi G., Zucker H. Ca2+ and Na+ permeability of high-threshold Ca2+ channels and their voltage-dependent block by Mg2+ ions in chick sensory neurones. J Physiol. 1997 Oct 1;504(Pt 1):1–15. doi: 10.1111/j.1469-7793.1997.001bf.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Carbone E., Lux H. D. Kinetics and selectivity of a low-voltage-activated calcium current in chick and rat sensory neurones. J Physiol. 1987 May;386:547–570. doi: 10.1113/jphysiol.1987.sp016551. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Cribbs L. L., Lee J. H., Yang J., Satin J., Zhang Y., Daud A., Barclay J., Williamson M. P., Fox M., Rees M. Cloning and characterization of alpha1H from human heart, a member of the T-type Ca2+ channel gene family. Circ Res. 1998 Jul 13;83(1):103–109. doi: 10.1161/01.res.83.1.103. [DOI] [PubMed] [Google Scholar]
  11. Dang T. X., McCleskey E. W. Ion channel selectivity through stepwise changes in binding affinity. J Gen Physiol. 1998 Feb;111(2):185–193. doi: 10.1085/jgp.111.2.185. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Dichtl A., Vierling W. Inhibition by magnesium of calcium inward current in heart ventricular muscle. Eur J Pharmacol. 1991 Nov 12;204(3):243–248. doi: 10.1016/0014-2999(91)90848-k. [DOI] [PubMed] [Google Scholar]
  13. Frazier C. J., George E. G., Jones S. W. Apparent change in ion selectivity caused by changes in intracellular K(+) during whole-cell recording. Biophys J. 2000 Apr;78(4):1872–1880. doi: 10.1016/S0006-3495(00)76736-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Fukushima Y., Hagiwara S. Currents carried by monovalent cations through calcium channels in mouse neoplastic B lymphocytes. J Physiol. 1985 Jan;358:255–284. doi: 10.1113/jphysiol.1985.sp015550. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. HODGKIN A. L., HUXLEY A. F. The components of membrane conductance in the giant axon of Loligo. J Physiol. 1952 Apr;116(4):473–496. doi: 10.1113/jphysiol.1952.sp004718. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Hagiwara S., Fukuda J., Eaton D. C. Membrane currents carried by Ca, Sr, and Ba in barnacle muscle fiber during voltage clamp. J Gen Physiol. 1974 May;63(5):564–578. doi: 10.1085/jgp.63.5.564. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Hall S. K., Fry C. H. Magnesium affects excitation, conduction, and contraction of isolated mammalian cardiac muscle. Am J Physiol. 1992 Aug;263(2 Pt 2):H622–H633. doi: 10.1152/ajpheart.1992.263.2.H622. [DOI] [PubMed] [Google Scholar]
  18. Hartzell H. C., White R. E. Effects of magnesium on inactivation of the voltage-gated calcium current in cardiac myocytes. J Gen Physiol. 1989 Oct;94(4):745–767. doi: 10.1085/jgp.94.4.745. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Hess P., Lansman J. B., Tsien R. W. Calcium channel selectivity for divalent and monovalent cations. Voltage and concentration dependence of single channel current in ventricular heart cells. J Gen Physiol. 1986 Sep;88(3):293–319. doi: 10.1085/jgp.88.3.293. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Hess P., Tsien R. W. Mechanism of ion permeation through calcium channels. 1984 May 31-Jun 6Nature. 309(5967):453–456. doi: 10.1038/309453a0. [DOI] [PubMed] [Google Scholar]
  21. Huguenard J. R. Low-threshold calcium currents in central nervous system neurons. Annu Rev Physiol. 1996;58:329–348. doi: 10.1146/annurev.ph.58.030196.001553. [DOI] [PubMed] [Google Scholar]
  22. Huguenard J. R., Prince D. A. A novel T-type current underlies prolonged Ca(2+)-dependent burst firing in GABAergic neurons of rat thalamic reticular nucleus. J Neurosci. 1992 Oct;12(10):3804–3817. doi: 10.1523/JNEUROSCI.12-10-03804.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Klugbauer N., Marais E., Lacinová L., Hofmann F. A T-type calcium channel from mouse brain. Pflugers Arch. 1999 Apr;437(5):710–715. doi: 10.1007/s004240050836. [DOI] [PubMed] [Google Scholar]
  24. Kuo C. C., Hess P. Block of the L-type Ca2+ channel pore by external and internal Mg2+ in rat phaeochromocytoma cells. J Physiol. 1993 Jul;466:683–706. [PMC free article] [PubMed] [Google Scholar]
  25. Lacinová L., Klugbauer N., Hofmann F. Regulation of the calcium channel alpha(1G) subunit by divalent cations and organic blockers. Neuropharmacology. 2000 Apr 27;39(7):1254–1266. doi: 10.1016/s0028-3908(99)00202-6. [DOI] [PubMed] [Google Scholar]
  26. 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]
  27. Lee J. H., Daud A. N., Cribbs L. L., Lacerda A. E., Pereverzev A., Klöckner U., Schneider T., Perez-Reyes E. Cloning and expression of a novel member of the low voltage-activated T-type calcium channel family. J Neurosci. 1999 Mar 15;19(6):1912–1921. doi: 10.1523/JNEUROSCI.19-06-01912.1999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Lee J. H., Gomora J. C., Cribbs L. L., Perez-Reyes E. Nickel block of three cloned T-type calcium channels: low concentrations selectively block alpha1H. Biophys J. 1999 Dec;77(6):3034–3042. doi: 10.1016/S0006-3495(99)77134-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Lux H. D., Carbone E., Zucker H. Na+ currents through low-voltage-activated Ca2+ channels of chick sensory neurones: block by external Ca2+ and Mg2+. J Physiol. 1990 Nov;430:159–188. doi: 10.1113/jphysiol.1990.sp018287. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. McCleskey E. W., Almers W. The Ca channel in skeletal muscle is a large pore. Proc Natl Acad Sci U S A. 1985 Oct;82(20):7149–7153. doi: 10.1073/pnas.82.20.7149. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. McCleskey E. W. Calcium channel permeation: A field in flux. J Gen Physiol. 1999 Jun;113(6):765–772. doi: 10.1085/jgp.113.6.765. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Monteil A., Chemin J., Bourinet E., Mennessier G., Lory P., Nargeot J. Molecular and functional properties of the human alpha(1G) subunit that forms T-type calcium channels. J Biol Chem. 2000 Mar 3;275(9):6090–6100. doi: 10.1074/jbc.275.9.6090. [DOI] [PubMed] [Google Scholar]
  33. Nonner W., Chen D. P., Eisenberg B. Progress and prospects in permeation. J Gen Physiol. 1999 Jun;113(6):773–782. doi: 10.1085/jgp.113.6.773. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Nonner W., Eisenberg B. Ion permeation and glutamate residues linked by Poisson-Nernst-Planck theory in L-type calcium channels. Biophys J. 1998 Sep;75(3):1287–1305. doi: 10.1016/S0006-3495(98)74048-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Perez-Reyes E., Cribbs L. L., Daud A., Lacerda A. E., Barclay J., Williamson M. P., Fox M., Rees M., Lee J. H. Molecular characterization of a neuronal low-voltage-activated T-type calcium channel. Nature. 1998 Feb 26;391(6670):896–900. doi: 10.1038/36110. [DOI] [PubMed] [Google Scholar]
  36. Serrano J. R., Perez-Reyes E., Jones S. W. State-dependent inactivation of the alpha1G T-type calcium channel. J Gen Physiol. 1999 Aug;114(2):185–201. doi: 10.1085/jgp.114.2.185. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Song Y., Liu Q. Y., Vassalle M. On the antiarrhythmic actions of magnesium in single guinea-pig ventricular myocytes. Clin Exp Pharmacol Physiol. 1996 Sep;23(9):830–838. doi: 10.1111/j.1440-1681.1996.tb01188.x. [DOI] [PubMed] [Google Scholar]
  38. Talley E. M., Cribbs L. L., Lee J. H., Daud A., Perez-Reyes E., Bayliss D. A. Differential distribution of three members of a gene family encoding low voltage-activated (T-type) calcium channels. J Neurosci. 1999 Mar 15;19(6):1895–1911. doi: 10.1523/JNEUROSCI.19-06-01895.1999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Wilson D. L., Morimoto K., Tsuda Y., Brown A. M. Interaction between calcium ions and surface charge as it relates to calcium currents. J Membr Biol. 1983;72(1-2):117–130. doi: 10.1007/BF01870319. [DOI] [PubMed] [Google Scholar]
  40. Woodhull A. M. Ionic blockage of sodium channels in nerve. J Gen Physiol. 1973 Jun;61(6):687–708. doi: 10.1085/jgp.61.6.687. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Wu J. Y., Lipsius S. L. Effects of extracellular Mg2+ on T- and L-type Ca2+ currents in single atrial myocytes. Am J Physiol. 1990 Dec;259(6 Pt 2):H1842–H1850. doi: 10.1152/ajpheart.1990.259.6.H1842. [DOI] [PubMed] [Google Scholar]
  42. Yang J., Ellinor P. T., Sather W. A., Zhang J. F., Tsien R. W. Molecular determinants of Ca2+ selectivity and ion permeation in L-type Ca2+ channels. Nature. 1993 Nov 11;366(6451):158–161. doi: 10.1038/366158a0. [DOI] [PubMed] [Google Scholar]
  43. Yue D. T., Marban E. Permeation in the dihydropyridine-sensitive calcium channel. Multi-ion occupancy but no anomalous mole-fraction effect between Ba2+ and Ca2+. J Gen Physiol. 1990 May;95(5):911–939. doi: 10.1085/jgp.95.5.911. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Zhang S., Sawanobori T., Adaniya H., Hirano Y., Hiraoka M. Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes. Am J Physiol. 1995 Jun;268(6 Pt 2):H2321–H2328. doi: 10.1152/ajpheart.1995.268.6.H2321. [DOI] [PubMed] [Google Scholar]
  45. Zhou W., Jones S. W. Surface charge and calcium channel saturation in bullfrog sympathetic neurons. J Gen Physiol. 1995 Apr;105(4):441–462. doi: 10.1085/jgp.105.4.441. [DOI] [PMC free article] [PubMed] [Google Scholar]

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