Skip to main content
NCBI home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1992 Nov;457:47–74. doi: 10.1113/jphysiol.1992.sp019364

A novel large-conductance Ca(2+)-activated potassium channel and current in nerve terminals of the rat neurohypophysis.

G Wang 1, P Thorn 1, J R Lemos 1
PMCID: PMC1175717  PMID: 1284313

Abstract

1. Nerve terminals of the rat posterior pituitary were acutely dissociated and identified using a combination of morphological and immunohistochemical techniques. Terminal membrane currents were studied using the 'whole-cell' patch clamp technique and channels were studied using inside-out and outside-out patches. 2. In physiological solutions, but with 7 mM 4-aminopyridine (4-AP), depolarizing voltage clamp steps from different holding potentials (-90 or -50 mV) elicited a fast, inward current followed by a slow, sustained, outward current. This outward current did not appear to show any steady-state inactivation. 3. The threshold for activation of the outward current was -30 mV and the current-voltage relation was 'bell-shaped'. The amplitude increased with increasingly depolarized potential steps. The outward current reversal potential was measured using tail current analysis and was consistent with that of a potassium current. 4. The sustained potassium current was determined to be dependent on the concentration of intracellular calcium. Extracellular Cd2+ (80 microM), a calcium channel blocker, also reversibly abolished the outward current. 5. The current was delayed in onset and was sustained over the length of a 150 ms-duration depolarizing pulse. The outward current reached a peak plateau and then decayed slowly. The decay was fitted by a single exponential with a time constant of 9.0 +/- 2.2 s. The decay constants did not show a dependence on voltage but rather on intracellular Ca2+. The time course of recovery from this decay was complex with full recovery taking > 190 s. 6. 4-AP (7 mM), dendrotoxin (100 nM), apamin (40-80 nM), and charybdotoxin (10-100 nM) had no effect on the sustained outward current. In contrast Ba2+ (200 microM) and tetraethylammonium inhibited the current, the latter in a dose-dependent manner (apparent concentration giving 50% of maximal inhibition (IC50) = 0.51 mM). 7. The neurohypophysial terminal outward current recorded here corresponds most closely to a Ca(2+)-activated K+ current (IK(Ca)) and not to a delayed rectifier or IA-like current. It also has properties different from that of the Ca(2+)-dependent outward current described in the magnocellular neuronal cell bodies of the hypothalamus. 8. A large conductance channel is often observed in isolated rat neurohypophysial nerve terminals. The channel had a unit conductance of 231 pS in symmetrical 150 mM K+.(ABSTRACT TRUNCATED AT 400 WORDS)

Full text

PDF
47

Selected References

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

  1. Adler E. M., Augustine G. J., Duffy S. N., Charlton M. P. Alien intracellular calcium chelators attenuate neurotransmitter release at the squid giant synapse. J Neurosci. 1991 Jun;11(6):1496–1507. doi: 10.1523/JNEUROSCI.11-06-01496.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Anderson C. S., MacKinnon R., Smith C., Miller C. Charybdotoxin block of single Ca2+-activated K+ channels. Effects of channel gating, voltage, and ionic strength. J Gen Physiol. 1988 Mar;91(3):317–333. doi: 10.1085/jgp.91.3.317. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Barrett J. N., Magleby K. L., Pallotta B. S. Properties of single calcium-activated potassium channels in cultured rat muscle. J Physiol. 1982 Oct;331:211–230. doi: 10.1113/jphysiol.1982.sp014370. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Berk D. A., Clark A., Jr, Hochmuth R. M. Analysis of lateral diffusion from a spherical cell surface to a tubular projection. Biophys J. 1992 Jan;61(1):1–8. doi: 10.1016/S0006-3495(92)81810-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Bicknell R. J., Brown D., Chapman C., Hancock P. D., Leng G. Reversible fatigue of stimulus-secretion coupling in the rat neurohypophysis. J Physiol. 1984 Mar;348:601–613. doi: 10.1113/jphysiol.1984.sp015128. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. 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]
  7. Bondy C. A., Gainer H., Russell J. T. Effects of stimulus frequency and potassium channel blockade on the secretion of vasopressin and oxytocin from the neurohypophysis. Neuroendocrinology. 1987 Sep;46(3):258–267. doi: 10.1159/000124829. [DOI] [PubMed] [Google Scholar]
  8. Bourque C. W. Activity-dependent modulation of nerve terminal excitation in a mammalian peptidergic system. Trends Neurosci. 1991 Jan;14(1):28–30. doi: 10.1016/0166-2236(91)90180-3. [DOI] [PubMed] [Google Scholar]
  9. Bourque C. W. Intraterminal recordings from the rat neurohypophysis in vitro. J Physiol. 1990 Feb;421:247–262. doi: 10.1113/jphysiol.1990.sp017943. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Bourque C. W. Transient calcium-dependent potassium current in magnocellular neurosecretory cells of the rat supraoptic nucleus. J Physiol. 1988 Mar;397:331–347. doi: 10.1113/jphysiol.1988.sp017004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Brown D. A., Constanti A., Adams P. R. Ca-activated potassium current in vertebrate sympathetic neurons. Cell Calcium. 1983 Dec;4(5-6):407–420. doi: 10.1016/0143-4160(83)90017-9. [DOI] [PubMed] [Google Scholar]
  12. Cazalis M., Dayanithi G., Nordmann J. J. Hormone release from isolated nerve endings of the rat neurohypophysis. J Physiol. 1987 Sep;390:55–70. doi: 10.1113/jphysiol.1987.sp016686. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Cazalis M., Dayanithi G., Nordmann J. J. The role of patterned burst and interburst interval on the excitation-coupling mechanism in the isolated rat neural lobe. J Physiol. 1985 Dec;369:45–60. doi: 10.1113/jphysiol.1985.sp015887. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Christensen O. Mediation of cell volume regulation by Ca2+ influx through stretch-activated channels. Nature. 1987 Nov 5;330(6143):66–68. doi: 10.1038/330066a0. [DOI] [PubMed] [Google Scholar]
  15. Cobbett P., Legendre P., Mason W. T. Characterization of three types of potassium current in cultured neurones of rat supraoptic nucleus area. J Physiol. 1989 Mar;410:443–462. doi: 10.1113/jphysiol.1989.sp017543. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Connor J. A., Stevens C. F. Inward and delayed outward membrane currents in isolated neural somata under voltage clamp. J Physiol. 1971 Feb;213(1):1–19. doi: 10.1113/jphysiol.1971.sp009364. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Farley J., Rudy B. Multiple types of voltage-dependent Ca2+-activated K+ channels of large conductance in rat brain synaptosomal membranes. Biophys J. 1988 Jun;53(6):919–934. doi: 10.1016/S0006-3495(88)83173-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. GARDOS G. The function of calcium in the potassium permeability of human erythrocytes. Biochim Biophys Acta. 1958 Dec;30(3):653–654. doi: 10.1016/0006-3002(58)90124-0. [DOI] [PubMed] [Google Scholar]
  19. Gainer H., Wolfe S. A., Jr, Obaid A. L., Salzberg B. M. Action potentials and frequency-dependent secretion in the mouse neurohypophysis. Neuroendocrinology. 1986;43(5):557–563. doi: 10.1159/000124582. [DOI] [PubMed] [Google Scholar]
  20. Grega D. S., Macdonald R. L. Activators of adenylate cyclase and cyclic AMP prolong calcium-dependent action potentials of mouse sensory neurons in culture by reducing a voltage-dependent potassium conductance. J Neurosci. 1987 Mar;7(3):700–707. doi: 10.1523/JNEUROSCI.07-03-00700.1987. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. 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]
  22. 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]
  23. Hermann A., Erxleben C. Charybdotoxin selectively blocks small Ca-activated K channels in Aplysia neurons. J Gen Physiol. 1987 Jul;90(1):27–47. doi: 10.1085/jgp.90.1.27. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Ikemoto Y., Ono K., Yoshida A., Akaike N. Delayed activation of large-conductance Ca2+-activated K channels in hippocampal neurons of the rat. Biophys J. 1989 Jul;56(1):207–212. doi: 10.1016/S0006-3495(89)82665-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Jackson M. B., Konnerth A., Augustine G. J. Action potential broadening and frequency-dependent facilitation of calcium signals in pituitary nerve terminals. Proc Natl Acad Sci U S A. 1991 Jan 15;88(2):380–384. doi: 10.1073/pnas.88.2.380. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Lancaster B., Nicoll R. A., Perkel D. J. Calcium activates two types of potassium channels in rat hippocampal neurons in culture. J Neurosci. 1991 Jan;11(1):23–30. doi: 10.1523/JNEUROSCI.11-01-00023.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Lancaster B., Nicoll R. A. Properties of two calcium-activated hyperpolarizations in rat hippocampal neurones. J Physiol. 1987 Aug;389:187–203. doi: 10.1113/jphysiol.1987.sp016653. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Lang D. G., Ritchie A. K. Large and small conductance calcium-activated potassium channels in the GH3 anterior pituitary cell line. Pflugers Arch. 1987 Dec;410(6):614–622. doi: 10.1007/BF00581321. [DOI] [PubMed] [Google Scholar]
  29. Lang D. G., Ritchie A. K. Tetraethylammonium blockade of apamin-sensitive and insensitive Ca2(+)-activated K+ channels in a pituitary cell line. J Physiol. 1990 Jun;425:117–132. doi: 10.1113/jphysiol.1990.sp018095. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Latorre R., Miller C. Conduction and selectivity in potassium channels. J Membr Biol. 1983;71(1-2):11–30. doi: 10.1007/BF01870671. [DOI] [PubMed] [Google Scholar]
  31. Lemos J. R., Nordmann J. J., Cooke I. M., Stuenkel E. L. Single channels and ionic currents in peptidergic nerve terminals. 1986 Jan 30-Feb 5Nature. 319(6052):410–412. doi: 10.1038/319410a0. [DOI] [PubMed] [Google Scholar]
  32. Lemos J. R., Nordmann J. J. Ionic channels and hormone release from peptidergic nerve terminals. J Exp Biol. 1986 Sep;124:53–72. doi: 10.1242/jeb.124.1.53. [DOI] [PubMed] [Google Scholar]
  33. Lemos J. R., Nowycky M. C. Two types of calcium channels coexist in peptide-releasing vertebrate nerve terminals. Neuron. 1989 May;2(5):1419–1426. doi: 10.1016/0896-6273(89)90187-6. [DOI] [PubMed] [Google Scholar]
  34. Llinás R. R. The intrinsic electrophysiological properties of mammalian neurons: insights into central nervous system function. Science. 1988 Dec 23;242(4886):1654–1664. doi: 10.1126/science.3059497. [DOI] [PubMed] [Google Scholar]
  35. Lux H. D., Neher E., Marty A. Single channel activity associated with the calcium dependent outward current in Helix pomatia. Pflugers Arch. 1981 Mar;389(3):293–295. doi: 10.1007/BF00584792. [DOI] [PubMed] [Google Scholar]
  36. 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]
  37. MacKinnon R., Reinhart P. H., White M. M. Charybdotoxin block of Shaker K+ channels suggests that different types of K+ channels share common structural features. Neuron. 1988 Dec;1(10):997–1001. doi: 10.1016/0896-6273(88)90156-0. [DOI] [PubMed] [Google Scholar]
  38. Marty A. Ca-dependent K channels with large unitary conductance in chromaffin cell membranes. Nature. 1981 Jun 11;291(5815):497–500. doi: 10.1038/291497a0. [DOI] [PubMed] [Google Scholar]
  39. McManus O. B., Magleby K. L. Kinetic states and modes of single large-conductance calcium-activated potassium channels in cultured rat skeletal muscle. J Physiol. 1988 Aug;402:79–120. doi: 10.1113/jphysiol.1988.sp017195. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Meech R. W. Calcium-dependent potassium activation in nervous tissues. Annu Rev Biophys Bioeng. 1978;7:1–18. doi: 10.1146/annurev.bb.07.060178.000245. [DOI] [PubMed] [Google Scholar]
  41. Meech R. W., Standen N. B. Potassium activation in Helix aspersa neurones under voltage clamp: a component mediated by calcium influx. J Physiol. 1975 Jul;249(2):211–239. doi: 10.1113/jphysiol.1975.sp011012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Miller C., Latorre R., Reisin I. Coupling of voltage-dependent gating and Ba++ block in the high-conductance, Ca++-activated K+ channel. J Gen Physiol. 1987 Sep;90(3):427–449. doi: 10.1085/jgp.90.3.427. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Miller C., Moczydlowski E., Latorre R., Phillips M. Charybdotoxin, a protein inhibitor of single Ca2+-activated K+ channels from mammalian skeletal muscle. Nature. 1985 Jan 24;313(6000):316–318. doi: 10.1038/313316a0. [DOI] [PubMed] [Google Scholar]
  44. Nachshen D. A. The early time course of potassium-stimulated calcium uptake in presynaptic nerve terminals isolated from rat brain. J Physiol. 1985 Apr;361:251–268. doi: 10.1113/jphysiol.1985.sp015644. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Nordmann J. J., Dayanithi G., Lemos J. R. Isolated neurosecretory nerve endings as a tool for studying the mechanism of stimulus-secretion coupling. Biosci Rep. 1987 May;7(5):411–426. doi: 10.1007/BF01362504. [DOI] [PubMed] [Google Scholar]
  46. Nordmann J. J., Desmazes J. P., Georgescauld D. The relationship between the membrane potential of neurosecretory nerve endings, as measured by a voltage-sensitive dye, and the release of neurohypophysial hormones. Neuroscience. 1982 Mar;7(3):731–737. doi: 10.1016/0306-4522(82)90078-1. [DOI] [PubMed] [Google Scholar]
  47. Nordmann J. J., Stuenkel E. L. Electrical properties of axons and neurohypophysial nerve terminals and their relationship to secretion in the rat. J Physiol. 1986 Nov;380:521–539. doi: 10.1113/jphysiol.1986.sp016300. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. 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]
  49. Petersen O. H., Maruyama Y. Calcium-activated potassium channels and their role in secretion. Nature. 1984 Feb 23;307(5953):693–696. doi: 10.1038/307693a0. [DOI] [PubMed] [Google Scholar]
  50. Poulain D. A., Wakerley J. B. Electrophysiology of hypothalamic magnocellular neurones secreting oxytocin and vasopressin. Neuroscience. 1982 Apr;7(4):773–808. doi: 10.1016/0306-4522(82)90044-6. [DOI] [PubMed] [Google Scholar]
  51. Reinhart P. H., Chung S., Levitan I. B. A family of calcium-dependent potassium channels from rat brain. Neuron. 1989 Jan;2(1):1031–1041. doi: 10.1016/0896-6273(89)90227-4. [DOI] [PubMed] [Google Scholar]
  52. Rogawski M. A. Transient outward current (IA) in clonal anterior pituitary cells: blockade by aminopyridine analogs. Naunyn Schmiedebergs Arch Pharmacol. 1988 Aug;338(2):125–132. doi: 10.1007/BF00174859. [DOI] [PubMed] [Google Scholar]
  53. Romey G., Lazdunski M. The coexistence in rat muscle cells of two distinct classes of Ca2+-dependent K+ channels with different pharmacological properties and different physiological functions. Biochem Biophys Res Commun. 1984 Jan 30;118(2):669–674. doi: 10.1016/0006-291x(84)91355-x. [DOI] [PubMed] [Google Scholar]
  54. Rudy B. Diversity and ubiquity of K channels. Neuroscience. 1988 Jun;25(3):729–749. doi: 10.1016/0306-4522(88)90033-4. [DOI] [PubMed] [Google Scholar]
  55. Salzberg B. M., Obaid A. L. Optical studies of the secretory event at vertebrate nerve terminals. J Exp Biol. 1988 Sep;139:195–231. doi: 10.1242/jeb.139.1.195. [DOI] [PubMed] [Google Scholar]
  56. Stuenkel E. L. Effects of membrane depolarization on intracellular calcium in single nerve terminals. Brain Res. 1990 Oct 8;529(1-2):96–101. doi: 10.1016/0006-8993(90)90815-s. [DOI] [PubMed] [Google Scholar]
  57. 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]
  58. Thorn P. J., Wang X. M., Lemos J. R. A fast, transient K+ current in neurohypophysial nerve terminals of the rat. J Physiol. 1991 Jan;432:313–326. doi: 10.1113/jphysiol.1991.sp018386. [DOI] [PMC free article] [PubMed] [Google Scholar]
  59. Tsien R. Y. New calcium indicators and buffers with high selectivity against magnesium and protons: design, synthesis, and properties of prototype structures. Biochemistry. 1980 May 27;19(11):2396–2404. doi: 10.1021/bi00552a018. [DOI] [PubMed] [Google Scholar]
  60. Turner T. J., Goldin S. M. Multiple components of synaptosomal [3H]-gamma-aminobutyric acid release resolved by a rapid superfusion system. Biochemistry. 1989 Jan 24;28(2):586–593. doi: 10.1021/bi00428a026. [DOI] [PubMed] [Google Scholar]
  61. Vergara C., Latorre R. Kinetics of Ca2+-activated K+ channels from rabbit muscle incorporated into planar bilayers. Evidence for a Ca2+ and Ba2+ blockade. J Gen Physiol. 1983 Oct;82(4):543–568. doi: 10.1085/jgp.82.4.543. [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Wang X. M., Treistman S. N., Lemos J. R. Direct identification of individual vasopressin-containing nerve terminals of the rat neurohypophysis after 'whole-cell' patch-clamp recordings. Neurosci Lett. 1991 Mar 11;124(1):125–128. doi: 10.1016/0304-3940(91)90838-k. [DOI] [PubMed] [Google Scholar]
  63. Wang X., Treistman S. N., Lemos J. R. Two types of high-threshold calcium currents inhibited by omega-conotoxin in nerve terminals of rat neurohypophysis. J Physiol. 1992 Jan;445:181–199. doi: 10.1113/jphysiol.1992.sp018919. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Wong B. S., Adler M. Tetraethylammonium blockade of calcium-activated potassium channels in clonal anterior pituitary cells. Pflugers Arch. 1986 Sep;407(3):279–284. doi: 10.1007/BF00585303. [DOI] [PubMed] [Google Scholar]
  65. Wong B. S., Lecar H., Adler M. Single calcium-dependent potassium channels in clonal anterior pituitary cells. Biophys J. 1982 Sep;39(3):313–317. doi: 10.1016/S0006-3495(82)84522-0. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from The Journal of Physiology are provided here courtesy of The Physiological Society

RESOURCES