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. 1986 Feb 1;87(2):305–326. doi: 10.1085/jgp.87.2.305

Two modes of gating during late Na+ channel currents in frog sartorius muscle

JB Patlak, M Ortiz
PMCID: PMC2217600  PMID: 2419486

Abstract

Na+ currents were measured during 0.4-s depolarizing pulses using the cell-attached variation of the patch-clamp technique. Patches on Cs-dialyzed segments of sartorius muscle of Rana pipiens contained an estimated 25-500 Na+ channels. Three distinct types of current were observed after the pulse onset: a large initial surge of inward current that decayed within 10 ms (early currents), a steady "drizzle" of isolated, brief, inward unitary currents (background currents), and occasional "cloudbursts" of tens to hundreds of sequential unitary inward currents (bursts). Average late currents (background plus bursts) were 0.12% of peak early current amplitude at -20 mV. 85% of the late currents were carried by bursting channels. The unit current amplitude was the same for all three types of current, with a conductance of 10.5 pS and a reversal potential of +74 mV. The magnitudes of the three current components were correlated from patch to patch, and all were eliminated by slow inactivation. We conclude that all three components were due to Na+ channel activity. The mean open time of the background currents was approximately 0.25 ms, and the channels averaged 1.2 openings for each event. Neither the open time nor the number of openings of background currents was strongly sensitive to membrane potential. We estimated that background openings occurred at a rate of 0.25 Hz for each channel. Bursts occurred once each 2,000 pulses for each channel (assuming identical channels). The open time during bursts increased with depolarization to 1-2 ms at -20 mV, whereas the closed time decreased to less than 20 ms. The fractional open time during bursts was fitted with m infinity 3 using standard Na+ channel models. We conclude that background currents are caused by a return of normal Na+ channels from inactivation, while bursts are instances where the channel's inactivation gate spontaneously loses its function for prolonged periods.

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Selected References

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  1. Adelman W. J., Jr, Palti Y. The effects of external potassium and long duration voltage conditioning on the amplitude of sodium currents in the giant axon of the squid, Loligo pealei. J Gen Physiol. 1969 Nov;54(5):589–606. doi: 10.1085/jgp.54.5.589. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Almers W., Stanfield P. R., Stühmer W. Lateral distribution of sodium and potassium channels in frog skeletal muscle: measurements with a patch-clamp technique. J Physiol. 1983 Mar;336:261–284. doi: 10.1113/jphysiol.1983.sp014580. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Almers W., Stanfield P. R., Stühmer W. Slow changes in currents through sodium channels in frog muscle membrane. J Physiol. 1983 Jun;339:253–271. doi: 10.1113/jphysiol.1983.sp014715. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Armstrong C. M., Bezanilla F., Rojas E. Destruction of sodium conductance inactivation in squid axons perfused with pronase. J Gen Physiol. 1973 Oct;62(4):375–391. doi: 10.1085/jgp.62.4.375. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Attwell D., Cohen I., Eisner D., Ohba M., Ojeda C. The steady state TTX-sensitive ("window") sodium current in cardiac Purkinje fibres. Pflugers Arch. 1979 Mar 16;379(2):137–142. doi: 10.1007/BF00586939. [DOI] [PubMed] [Google Scholar]
  6. Bezanilla F., Armstrong C. M. Inactivation of the sodium channel. I. Sodium current experiments. J Gen Physiol. 1977 Nov;70(5):549–566. doi: 10.1085/jgp.70.5.549. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Campbell D. T., Hille B. Kinetic and pharmacological properties of the sodium channel of frog skeletal muscle. J Gen Physiol. 1976 Mar;67(3):309–323. doi: 10.1085/jgp.67.3.309. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Chandler W. K., Meves H. Evidence for two types of sodium conductance in axons perfused with sodium fluoride solution. J Physiol. 1970 Dec;211(3):653–678. doi: 10.1113/jphysiol.1970.sp009298. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Collins C. A., Rojas E., Suarez-Isla B. A. Activation and inactivation characteristics of the sodium permeability in muscle fibres from Rana temporaria. J Physiol. 1982 Mar;324:297–318. doi: 10.1113/jphysiol.1982.sp014114. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Conti F., Neumcke B., Nonner W., Stämpfli R. Conductance fluctuations from the inactivation process of sodium channels in myelinated nerve fibres. J Physiol. 1980 Nov;308:217–239. doi: 10.1113/jphysiol.1980.sp013469. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Dubois J. M., Bergman C. Late sodium current in the node of Ranvier. Pflugers Arch. 1975;357(1-2):145–148. doi: 10.1007/BF00584552. [DOI] [PubMed] [Google Scholar]
  12. French R. J., Horn R. Sodium channel gating: models, mimics, and modifiers. Annu Rev Biophys Bioeng. 1983;12:319–356. doi: 10.1146/annurev.bb.12.060183.001535. [DOI] [PubMed] [Google Scholar]
  13. Gintant G. A., Datyner N. B., Cohen I. S. Slow inactivation of a tetrodotoxin-sensitive current in canine cardiac Purkinje fibers. Biophys J. 1984 Mar;45(3):509–512. doi: 10.1016/S0006-3495(84)84187-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. 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]
  15. 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]
  16. Hess P., Lansman J. B., Tsien R. W. Different modes of Ca channel gating behaviour favoured by dihydropyridine Ca agonists and antagonists. Nature. 1984 Oct 11;311(5986):538–544. doi: 10.1038/311538a0. [DOI] [PubMed] [Google Scholar]
  17. Hille B., Campbell D. T. An improved vaseline gap voltage clamp for skeletal muscle fibers. J Gen Physiol. 1976 Mar;67(3):265–293. doi: 10.1085/jgp.67.3.265. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Horn R., Vandenberg C. A., Lange K. Statistical analysis of single sodium channels. Effects of N-bromoacetamide. Biophys J. 1984 Jan;45(1):323–335. doi: 10.1016/S0006-3495(84)84158-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. McAllister R. E., Noble D., Tsien R. W. Reconstruction of the electrical activity of cardiac Purkinje fibres. J Physiol. 1975 Sep;251(1):1–59. doi: 10.1113/jphysiol.1975.sp011080. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Moczydlowski E., Garber S. S., Miller C. Batrachotoxin-activated Na+ channels in planar lipid bilayers. Competition of tetrodotoxin block by Na+. J Gen Physiol. 1984 Nov;84(5):665–686. doi: 10.1085/jgp.84.5.665. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Neher E. The charge carried by single-channel currents of rat cultured muscle cells in the presence of local anaesthetics. J Physiol. 1983 Jun;339:663–678. doi: 10.1113/jphysiol.1983.sp014741. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Oxford G. S. Some kinetic and steady-state properties of sodium channels after removal of inactivation. J Gen Physiol. 1981 Jan;77(1):1–22. doi: 10.1085/jgp.77.1.1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Oxford G. S., Yeh J. Z. Interactions of monovalent cations with sodium channels in squid axon. I. Modification of physiological inactivation gating. J Gen Physiol. 1985 Apr;85(4):583–602. doi: 10.1085/jgp.85.4.583. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Patlak J. B., Gration K. A., Usherwood P. N. Single glutamate-activated channels in locust muscle. Nature. 1979 Apr 12;278(5705):643–645. doi: 10.1038/278643a0. [DOI] [PubMed] [Google Scholar]
  25. Patlak J. B., Ortiz M. Slow currents through single sodium channels of the adult rat heart. J Gen Physiol. 1985 Jul;86(1):89–104. doi: 10.1085/jgp.86.1.89. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Patlak J., Horn R. Effect of N-bromoacetamide on single sodium channel currents in excised membrane patches. J Gen Physiol. 1982 Mar;79(3):333–351. doi: 10.1085/jgp.79.3.333. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Reuter H. Slow inactivation of currents in cardiac Purkinje fibres. J Physiol. 1968 Jul;197(1):233–253. doi: 10.1113/jphysiol.1968.sp008557. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Rudy B. Slow inactivation of the sodium conductance in squid giant axons. Pronase resistance. J Physiol. 1978 Oct;283:1–21. doi: 10.1113/jphysiol.1978.sp012485. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Shoukimas J. J., French R. J. Incomplete inactivation of sodium currents in nonperfused squid axon. Biophys J. 1980 Nov;32(2):857–862. doi: 10.1016/S0006-3495(80)85021-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Sigworth F. J. Covariance of nonstationary sodium current fluctuations at the node of Ranvier. Biophys J. 1981 Apr;34(1):111–133. doi: 10.1016/S0006-3495(81)84840-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Sigworth F. J., Neher E. Single Na+ channel currents observed in cultured rat muscle cells. Nature. 1980 Oct 2;287(5781):447–449. doi: 10.1038/287447a0. [DOI] [PubMed] [Google Scholar]
  32. Sigworth F. J. The variance of sodium current fluctuations at the node of Ranvier. J Physiol. 1980 Oct;307:97–129. doi: 10.1113/jphysiol.1980.sp013426. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Vandenberg C. A., Horn R. Inactivation viewed through single sodium channels. J Gen Physiol. 1984 Oct;84(4):535–564. doi: 10.1085/jgp.84.4.535. [DOI] [PMC free article] [PubMed] [Google Scholar]

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