Abstract
Internal application of millimolar concentrations of calcium to batrachotoxin (BTX)-activated rat skeletal muscle sodium channels, bathed symmetrically in 200 mm NaCl, causes a reduction in apparent singlechannel amplitude without visibly increasing noise at a bandwidth of 50 Hz. A greater calcium-induced reduction occurred upon removal of external sodium ions. Internal calcium acted similarly in high ionic strength solutions (3m NaCl), where surface charges are effectively screened, suggesting that calcium acts, in part, by binding within the pore and occluding the conducting pathway. In low ionic strength solutions (20 mm NaCl), internal addition of N-Methyl-Glucamine (NMG) ions decreased the single channel amplitude consistent with screening of negative surface charges. An accurate description of the dose dependence of calcium inhibition, using either a simple blocking model, or rate theory calculations of ion permeation and block, also required surface charge screening. Hence, our data support the view that sodium current inhibition by internal calcium arises from a combination of both open-channel block and surface charge effects.
Similar content being viewed by others
References
Albitz, R., Magyar, J., Nilius, B. 1990. Block of single cardiac sodium channels by intracellular magnesium. Eur. Biophys. J. 19:19–23
Alvarez, O., Villaroel, A., Eisenmann, G. 1992. Calculation of ion currents from energy profiles and energy profiles from ion currents in a multibarrier, multisite, multioccupancy channel model. Methods. Enzymol. 207:816–854
Cukierman, S. 1993. Barium modulates the gating of batrachotoxintreated Na+ channels in high ionic strength solutions. Biophys. J. 65:1168–1173
French, R.J. Worley III, J.F., Wonderlin, W.F., Kularatna, A.S., Krueger, B.K. 1994. Ion permeation, divalent cation block, and chemical modification of single sodium channels. Description by single-and double-occupancy rate theory models. J. Gen. Physiol. 13:447–470
Green, W.N., Andersen, O.S. 1991. Surface charges and ion channel function. Ann. Rev. Physiol. 53:341–359
Green, W.N., Weiss, L.B., Andersen, O.S. 1987. Batrachotoxinmodified sodium channels in planar lipid bilayers. Ion permeation and block. J. Gen. Physiol. 89:841–872
Latorre, R., Labarca, B., and Naranjo, D. 1992. Surface charge effects on ion conduction in ion channels. Methods in Enzymology 207:471–501
MacKinnon, R., Latorre, R., Miller, C. 1989. Role of surface charges in the operation of a high-conductance Ca2+-activated K+ channel. Biochemistry 28:8092–8099
Moczydlowski, E. 1993. Profiles of permeation through Na-channels. Biophys. J. 64:1051–1052
Moczydlowski, E., Uehara, A.S., Guo, X., Heiny, J. 1986. Isochannels and blocking modes of voltage-dependent sodium channels. Ann. N.Y. Acad. Sci. 479:269–292
Naranjo, D., Latorre, R. 1993. Ion conduction in substates of the batrachotoxin-modified Na+ channel from toad skeletal muscle. Biophys. J. 64:1038–1050
Pusch, M., Conti, F., Stühmer, W. 1989. Intracellular magnesium blocks sodium outward currents in a voltageand dose-dependent manner. Biophys. J. 55:1267–1271
Ravindran, A., Kwiecinski, H., Alvarez, O., Eisenmann, G., Moczydowski, E. 1992. Modeling ion permeation through batrachotoxinmodified Na+ channels from rat skeletal muscle with a multi ion pore. Biophys. J. 61:494–508
Wang, G.K. 1988. Cocaine-induced closures of single batrachotoxinactivated Na+ channels in planar lipid bilayers. J. Gen. Physiol. 92:747–765
Zamponi, G.W., Doyle, D.D., French, R.J. 1993. Fast lidocaine block of cardiac and skeletal muscle sodium channels. One site with two routes of access. Biophys. J. 65:80–90
Zamponi, G.W., French, R.J. 1993. Dissecting lidocaine action: Diethylamine and phenol mimic separate modes of lidocaine block of sodium channels from heart and skeletal muscle. Biophys. J. 65:2335–2347
Zamponi, G.W., French, R.J. 1994. Amine blockers of the cytoplasmic mouth of sodium channels: A small structural change can abolish voltage dependence. Biophys. J. 67:1015–1027
Author information
Authors and Affiliations
Additional information
This research was supported by grants from the Medical Research Council of Canada, and by a Scholarship to R.J. French from the Alberta Heritage Foundation for Medical Research. We thank Dr. John Daly for providing batrachotoxin, and Drs. Lawrence Haynes, Christopher Miller, David Naranjo, and John Hanrahan for helpful comments on various versions of the manuscript.
Rights and permissions
About this article
Cite this article
Zamponi, G.W., French, R.J. Sodium current inhibition by internal calcium: A combination of open-channel block and surface charge screening?. J. Membarin Biol. 147, 1–6 (1995). https://doi.org/10.1007/BF00235393
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00235393