Membrane currents in visually identified motoneurones of neonatal rat spinal cord (original) (raw)

Abstract

1. Ionic currents induced by depolarization of motoneurones were analysed by tight-seal, whole-cell recording in thin slices of neonatal rat lumbar spinal cord. Identification of motoneurones viewed under Nomarski optics was confirmed by retrograde labelling with the fluorescent dye, Evans Blue. 2. Under whole-cell voltage clamp, depolarizing command pulses from a holding potential of about -70 mV evoked a fast inward current followed by an outward current. The former was suppressed either by lowering external Na+ concentration or by application of tetrodotoxin (TTX). The apparent dissociation constant of TTX was about 13 nM. 3. The outward current remaining after TTX application was activated by depolarization above -50 mV, showing marked outward rectification in the current-voltage relation. Outward tail currents reversed in polarity near the K+ equilibrium potential calculated from the external and pipette K+ concentrations. 4. When external Ca2+ was replaced by Mg2+, the outward K+ current was suppressed markedly and reversibly. Subtraction of current recorded in Ca2+-free-Mg2+ solution from that in control solution revealed a Ca2(+)-dependent K+ current, IK(Ca) with both a transient, IC, and a sustained component IAHP; its tail current lasted for several hundred milliseconds. 5. The sustained outward current observed in Ca2(+)-free-Mg2+ solution was largely suppressed by external application of tetraethylammonium chloride (30 mM), suggesting that it was mostly the delayed rectifier current, IK. In Ca2(+)-free-Mg2+ solution containing TEA and TTX, another transient outward current was observed, which was inactivated by depolarizing pre-pulses in a time- and voltage-dependent manner. The steady-state inactivation curve indicated 50% inactivation at about -77 mV. 4-Aminopyridine (4-AP, 4 mM) largely and reversibly suppressed this current, whereas it did not affect IK observed in the absence of TEA. It is suggested that the transient outward current corresponds to the A-current (IA). 6. Action potentials were recorded in current-clamp mode. Replacement of external Ca2+ by Mg2+ markedly diminished the after-hyperpolarization. Concomitantly, the repolarizing phase of action potentials was slightly prolonged. In Ca2(+)-free-Mg2+ solution, application of 4-AP markedly prolonged action potential repolarization. In Ca2(+)-free-Mg2+ solution containing 4-AP, addition of TEA-Cl further prolonged the duration of the action potential. It is concluded that three different potassium currents, IC, IA and IK may all contribute to action potential repolarization in rat spinal motoneurones.

27

Images in this article

Selected References

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

  1. ARAKI T., TERZUOLO C. A. Membrane currents in spinal motoneurons associated with the action potential and synaptic activity. J Neurophysiol. 1962 Nov;25:772–789. doi: 10.1152/jn.1962.25.6.772. [DOI] [PubMed] [Google Scholar]
  2. Adams P. R., Brown D. A., Constanti A. M-currents and other potassium currents in bullfrog sympathetic neurones. J Physiol. 1982 Sep;330:537–572. doi: 10.1113/jphysiol.1982.sp014357. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Adams P. R., Constanti A., Brown D. A., Clark R. B. Intracellular Ca2+ activates a fast voltage-sensitive K+ current in vertebrate sympathetic neurones. Nature. 1982 Apr 22;296(5859):746–749. doi: 10.1038/296746a0. [DOI] [PubMed] [Google Scholar]
  4. Adams P. R., Galvan M. Voltage-dependent currents of vertebrate neurons and their role in membrane excitability. Adv Neurol. 1986;44:137–170. [PubMed] [Google Scholar]
  5. BROCK L. G., COOMBS J. S., ECCLES J. C. Intracellular recording from antidromically activated motoneurones. J Physiol. 1953 Dec 29;122(3):429–461. doi: 10.1113/jphysiol.1953.sp005013. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Bader C. R., Bernheim L., Bertrand D. Sodium-activated potassium current in cultured avian neurones. Nature. 1985 Oct 10;317(6037):540–542. doi: 10.1038/317540a0. [DOI] [PubMed] [Google Scholar]
  7. Barrett J. N., Crill W. E. Voltage clamp of cat motoneurone somata: properties of the fast inward current. J Physiol. 1980 Jul;304:231–249. doi: 10.1113/jphysiol.1980.sp013322. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Belluzzi O., Sacchi O., Wanke E. A fast transient outward current in the rat sympathetic neurone studied under voltage-clamp conditions. J Physiol. 1985 Jan;358:91–108. doi: 10.1113/jphysiol.1985.sp015542. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Blatz A. L., Magleby K. L. Single apamin-blocked Ca-activated K+ channels of small conductance in cultured rat skeletal muscle. Nature. 1986 Oct 23;323(6090):718–720. doi: 10.1038/323718a0. [DOI] [PubMed] [Google Scholar]
  10. COOMBS J. S., ECCLES J. C., FATT P. The electrical properties of the motoneurone membrane. J Physiol. 1955 Nov 28;130(2):291–325. doi: 10.1113/jphysiol.1955.sp005411. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Catterall W. A. Localization of sodium channels in cultured neural cells. J Neurosci. 1981 Jul;1(7):777–783. doi: 10.1523/JNEUROSCI.01-07-00777.1981. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Connor J. A., Stevens C. F. Voltage clamp studies of a transient outward membrane current in gastropod neural somata. J Physiol. 1971 Feb;213(1):21–30. doi: 10.1113/jphysiol.1971.sp009365. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Constanti A., Sim J. A. Calcium-dependent potassium conductance in guinea-pig olfactory cortex neurones in vitro. J Physiol. 1987 Jun;387:173–194. doi: 10.1113/jphysiol.1987.sp016569. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Dryer S. E., Fujii J. T., Martin A. R. A Na+-activated K+ current in cultured brain stem neurones from chicks. J Physiol. 1989 Mar;410:283–296. doi: 10.1113/jphysiol.1989.sp017533. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Edwards F. A., Konnerth A., Sakmann B., Takahashi T. A thin slice preparation for patch clamp recordings from neurones of the mammalian central nervous system. Pflugers Arch. 1989 Sep;414(5):600–612. doi: 10.1007/BF00580998. [DOI] [PubMed] [Google Scholar]
  16. Fenwick E. M., Marty A., Neher E. A patch-clamp study of bovine chromaffin cells and of their sensitivity to acetylcholine. J Physiol. 1982 Oct;331:577–597. doi: 10.1113/jphysiol.1982.sp014393. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Fulton B. P., Miledi R., Takahashi T. Electrical synapses between motoneurons in the spinal cord of the newborn rat. Proc R Soc Lond B Biol Sci. 1980 Jun 23;208(1170):115–120. doi: 10.1098/rspb.1980.0045. [DOI] [PubMed] [Google Scholar]
  18. Fulton B. P., Walton K. Electrophysiological properties of neonatal rat motoneurones studied in vitro. J Physiol. 1986 Jan;370:651–678. doi: 10.1113/jphysiol.1986.sp015956. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Gustafsson B., Galvan M., Grafe P., Wigström H. A transient outward current in a mammalian central neurone blocked by 4-aminopyridine. Nature. 1982 Sep 16;299(5880):252–254. doi: 10.1038/299252a0. [DOI] [PubMed] [Google Scholar]
  20. HAGIWARA S., KUSANO K., SAITO N. Membrane changes of Onchidium nerve cell in potassium-rich media. J Physiol. 1961 Mar;155:470–489. doi: 10.1113/jphysiol.1961.sp006640. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. HODGKIN A. L., HUXLEY A. F. The dual effect of membrane potential on sodium conductance in the giant axon of Loligo. J Physiol. 1952 Apr;116(4):497–506. doi: 10.1113/jphysiol.1952.sp004719. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Hagiwara S., Ohmori H. Studies of calcium channels in rat clonal pituitary cells with patch electrode voltage clamp. J Physiol. 1982 Oct;331:231–252. doi: 10.1113/jphysiol.1982.sp014371. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. 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]
  24. Harada Y., Takahashi T. The calcium component of the action potential in spinal motoneurones of the rat. J Physiol. 1983 Feb;335:89–100. doi: 10.1113/jphysiol.1983.sp014521. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Hartung K. Potentiation of a transient outward current by Na+ influx in crayfish neurones. Pflugers Arch. 1985 May;404(1):41–44. doi: 10.1007/BF00581488. [DOI] [PubMed] [Google Scholar]
  26. MacDermott A. B., Weight F. F. Action potential repolarization may involve a transient, Ca2+-sensitive outward current in a vertebrate neurone. Nature. 1982 Nov 11;300(5888):185–188. doi: 10.1038/300185a0. [DOI] [PubMed] [Google Scholar]
  27. Neher E. The use of the patch clamp technique to study second messenger-mediated cellular events. Neuroscience. 1988 Sep;26(3):727–734. doi: 10.1016/0306-4522(88)90094-2. [DOI] [PubMed] [Google Scholar]
  28. Noda M., Ikeda T., Suzuki H., Takeshima H., Takahashi T., Kuno M., Numa S. Expression of functional sodium channels from cloned cDNA. 1986 Aug 28-Sep 3Nature. 322(6082):826–828. doi: 10.1038/322826a0. [DOI] [PubMed] [Google Scholar]
  29. Otsuka M., Konishi S. Electrophysiology of mammalian spinal cord in vitro. Nature. 1974 Dec 20;252(5485):733–734. doi: 10.1038/252733a0. [DOI] [PubMed] [Google Scholar]
  30. Pennefather P., Lancaster B., Adams P. R., Nicoll R. A. Two distinct Ca-dependent K currents in bullfrog sympathetic ganglion cells. Proc Natl Acad Sci U S A. 1985 May;82(9):3040–3044. doi: 10.1073/pnas.82.9.3040. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Schwindt P. C., Crill W. E. Differential effects of TEA and cations on outward ionic currents of cat motoneurons. J Neurophysiol. 1981 Jul;46(1):1–16. doi: 10.1152/jn.1981.46.1.1. [DOI] [PubMed] [Google Scholar]
  32. Segal M., Rogawski M. A., Barker J. L. A transient potassium conductance regulates the excitability of cultured hippocampal and spinal neurons. J Neurosci. 1984 Feb;4(2):604–609. doi: 10.1523/JNEUROSCI.04-02-00604.1984. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Storm J. F. Action potential repolarization and a fast after-hyperpolarization in rat hippocampal pyramidal cells. J Physiol. 1987 Apr;385:733–759. doi: 10.1113/jphysiol.1987.sp016517. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Storm J. F. Temporal integration by a slowly inactivating K+ current in hippocampal neurons. Nature. 1988 Nov 24;336(6197):379–381. doi: 10.1038/336379a0. [DOI] [PubMed] [Google Scholar]
  35. Takahashi T., Berger A. J. Direct excitation of rat spinal motoneurones by serotonin. J Physiol. 1990 Apr;423:63–76. doi: 10.1113/jphysiol.1990.sp018011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Takahashi T. Intracellular recording from visually identified motoneurons in rat spinal cord slices. Proc R Soc Lond B Biol Sci. 1978 Jul 26;202(1148):417–421. doi: 10.1098/rspb.1978.0076. [DOI] [PubMed] [Google Scholar]
  37. Takahashi T. Inward rectification in neonatal rat spinal motoneurones. J Physiol. 1990 Apr;423:47–62. doi: 10.1113/jphysiol.1990.sp018010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Thompson S. H. Three pharmacologically distinct potassium channels in molluscan neurones. J Physiol. 1977 Feb;265(2):465–488. doi: 10.1113/jphysiol.1977.sp011725. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Walton K., Fulton B. P. Ionic mechanisms underlying the firing properties of rat neonatal motoneurons studied in vitro. Neuroscience. 1986 Nov;19(3):669–683. doi: 10.1016/0306-4522(86)90291-5. [DOI] [PubMed] [Google Scholar]
  40. Williams J. T., North R. A., Shefner S. A., Nishi S., Egan T. M. Membrane properties of rat locus coeruleus neurones. Neuroscience. 1984 Sep;13(1):137–156. doi: 10.1016/0306-4522(84)90265-3. [DOI] [PubMed] [Google Scholar]
  41. Zbicz K. L., Weight F. F. Transient voltage and calcium-dependent outward currents in hippocampal CA3 pyramidal neurons. J Neurophysiol. 1985 Apr;53(4):1038–1058. doi: 10.1152/jn.1985.53.4.1038. [DOI] [PubMed] [Google Scholar]