Skip to main content
NCBI home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1988 Nov;405:577–593. doi: 10.1113/jphysiol.1988.sp017349

Whole-cell recordings of ionic currents in bovine somatotrophs and their involvement in growth hormone secretion.

W T Mason 1, S R Rawlings 1
PMCID: PMC1190992  PMID: 2475612

Abstract

1. The whole-cell mode of the patch-clamp technique was used to record voltage-activated cationic currents in immunocytochemically identified bovine somatotrophs. 2. In current-clamp mode, cells had a resting membrane potential of -83.0 +/- 4.5 mV, and an input resistance of 8.4 +/- 2.1 G omega. Cells rarely fired action potentials spontaneously, but fired one to three action potentials in response to a suprathreshold current pulse. 3. Under voltage clamp, in Ca2+-free media, the action potential was shown to be composed of a TTX-sensitive inward Na+ current and an outward K+ current. 4. The isolated Na+ current had a threshold of approximately -50 mV, and rapidly activated and then inactivated to a small steady-state current. Peak Na+ current amplitude with 140 mM-external Na+ was 341.1 +/- 33.5 pA (n = 14) at a membrane potential of -32.1 +/- 2.4 mV (n = 14). 5. With Ca2+ or Ba2+ (5-30 mM) as the only membrane-permeable cation, voltage pulses to potentials more positive than -55 mV from a holding potential of -80 mV revealed a rapidly activating current component that was followed by a second, very slowly inactivating, current component, most clearly seen with Ba2+. Both components were maximally activated between 0 and +10 mV, were TTX insensitive, but were blocked by 4 mM-Co2+. 6. Three components of the isolated K+ current were identified (IA, IK and IK(Ca] by their voltage sensitivity, Ca2+ dependence and their response to 4-aminopyridine (4-AP) and tetraethylammonium (TEA). 7. Growth hormone (GH)-releasing hormone (GHRH) applied to cells under whole-cell voltage clamp had no effect on either steady-state or voltage-activated ionic currents. This is probably due to dialysis of cytoplasmic compounds vital for GHRH activation of the cell. 8. Both basal and GHRH-stimulated GH secretion were unaffected by TTX, implying that the Na+ action potential is not critical for such release. In contrast the Ca2+ channel blocker Co2+ attenuated GH release in both cases. The K+ channel blocker TEA stimulated GH release above basal and GHRH-stimulated levels.

Full text

PDF
577

Images in this article

580Fig. 1
on p.580
587Fig. 8
on p.587

Selected References

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

  1. Barker J. L., Dufy B., Owen D. G., Segal M. Excitable membrane properties of cultured central nervous system neurons and clonal pituitary cells. Cold Spring Harb Symp Quant Biol. 1983;48(Pt 1):259–268. doi: 10.1101/sqb.1983.048.01.028. [DOI] [PubMed] [Google Scholar]
  2. Barros F., Katz G. M., Kaczorowski G. J., Vandlen R. L., Reuben J. P. Calcium currents in GH3 cultured pituitary cells under whole-cell voltage-clamp: inhibition by voltage-dependent potassium currents. Proc Natl Acad Sci U S A. 1985 Feb;82(4):1108–1112. doi: 10.1073/pnas.82.4.1108. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Carbone E., Lux H. D. A low voltage-activated calcium conductance in embryonic chick sensory neurons. Biophys J. 1984 Sep;46(3):413–418. doi: 10.1016/S0006-3495(84)84037-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Cobbett P., Ingram C. D., Mason W. T. Sodium and potassium currents involved in action potential propagation in normal bovine lactotrophs. J Physiol. 1987 Nov;392:273–299. doi: 10.1113/jphysiol.1987.sp016780. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Cobbett P., Ingram C. D., Mason W. T. Voltage-activated currents through calcium channels in normal bovine lactotrophs. Neuroscience. 1987 Nov;23(2):661–677. doi: 10.1016/0306-4522(87)90084-4. [DOI] [PubMed] [Google Scholar]
  6. Conn P. M., Rogers D. C. Gonadotropin release from pituitary cultures following activation of endogenous ion channels. Endocrinology. 1980 Dec;107(6):2133–2134. doi: 10.1210/endo-107-6-2133. [DOI] [PubMed] [Google Scholar]
  7. Dubinsky J. M., Oxford G. S. Dual modulation of K channels by thyrotropin-releasing hormone in clonal pituitary cells. Proc Natl Acad Sci U S A. 1985 Jun;82(12):4282–4286. doi: 10.1073/pnas.82.12.4282. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Dubinsky J. M., Oxford G. S. Ionic currents in two strains of rat anterior pituitary tumor cells. J Gen Physiol. 1984 Mar;83(3):309–339. doi: 10.1085/jgp.83.3.309. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Dufy B., Jaken S., Barker J. L. Intracellular Ca2+-dependent protein kinase C activation mimics delayed effects of thyrotropin-releasing hormone on clonal pituitary cell excitability. Endocrinology. 1987 Aug;121(2):793–802. doi: 10.1210/endo-121-2-793. [DOI] [PubMed] [Google Scholar]
  10. Eckert R., Tillotson D. L. Calcium-mediated inactivation of the calcium conductance in caesium-loaded giant neurones of Aplysia californica. J Physiol. 1981 May;314:265–280. doi: 10.1113/jphysiol.1981.sp013706. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. FRANKENHAEUSER B., HODGKIN A. L. The action of calcium on the electrical properties of squid axons. J Physiol. 1957 Jul 11;137(2):218–244. doi: 10.1113/jphysiol.1957.sp005808. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. 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]
  13. 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]
  14. Israel J. M., Denef C., Vincent J. D. Electrophysiological properties of normal somatotrophs in culture. An intracellular study. Neuroendocrinology. 1983 Sep;37(3):193–199. doi: 10.1159/000123542. [DOI] [PubMed] [Google Scholar]
  15. Kidokoro Y. Spontaneous calcium action potentials in a clonal pituitary cell line and their relationship to prolactin secretion. Nature. 1975 Dec 25;258(5537):741–742. doi: 10.1038/258741a0. [DOI] [PubMed] [Google Scholar]
  16. Lingle C. J., Sombati S., Freeman M. E. Membrane currents in identified lactotrophs of rat anterior pituitary. J Neurosci. 1986 Oct;6(10):2995–3005. doi: 10.1523/JNEUROSCI.06-10-02995.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Marchetti C., Childs G. V., Brown A. M. Membrane currents of identified isolated rat corticotropes and gonadotropes. Am J Physiol. 1987 Mar;252(3 Pt 1):E340–E346. doi: 10.1152/ajpendo.1987.252.3.E340. [DOI] [PubMed] [Google Scholar]
  18. Mason W. T., Ingram C. D. Techniques for studying the role of electrical activity in control of secretion by normal anterior pituitary cells. Methods Enzymol. 1986;124:207–242. doi: 10.1016/0076-6879(86)24017-3. [DOI] [PubMed] [Google Scholar]
  19. Mason W. T., Sikdar S. K. Characterization of voltage-gated sodium channels in ovine gonadotrophs: relationship to hormone secretion. J Physiol. 1988 May;399:493–517. doi: 10.1113/jphysiol.1988.sp017093. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Mason W. T., Waring D. W. Electrophysiological recordings from gonadotrophs. Evidence for Ca2+ channels mediated by gonadotrophin-releasing hormone. Neuroendocrinology. 1985 Sep;41(3):258–268. doi: 10.1159/000124186. [DOI] [PubMed] [Google Scholar]
  21. Matteson D. R., Armstrong C. M. Na and Ca channels in a transformed line of anterior pituitary cells. J Gen Physiol. 1984 Mar;83(3):371–394. doi: 10.1085/jgp.83.3.371. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Matteson D. R., Armstrong C. M. Properties of two types of calcium channels in clonal pituitary cells. J Gen Physiol. 1986 Jan;87(1):161–182. doi: 10.1085/jgp.87.1.161. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Narahashi T., Tsunoo A., Yoshii M. Characterization of two types of calcium channels in mouse neuroblastoma cells. J Physiol. 1987 Feb;383:231–249. doi: 10.1113/jphysiol.1987.sp016406. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Nussinovitch I. Growth hormone releasing factor evokes rhythmic hyperpolarizing currents in rat anterior pituitary cells. J Physiol. 1988 Jan;395:303–318. doi: 10.1113/jphysiol.1988.sp016920. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Ritchie A. K. Thyrotropin-releasing hormone stimulates a calcium-activated potassium current in a rat anterior pituitary cell line. J Physiol. 1987 Apr;385:611–625. doi: 10.1113/jphysiol.1987.sp016510. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Ritchie A. K. Two distinct calcium-activated potassium currents in a rat anterior pituitary cell line. J Physiol. 1987 Apr;385:591–609. doi: 10.1113/jphysiol.1987.sp016509. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Sand O., Haug E., Gautvik K. M. Effects of thyroliberin and 4-aminopyridine on action potentials and prolactin release and synthesis in rat pituitary cells in culture. Acta Physiol Scand. 1980 Mar;108(3):247–252. doi: 10.1111/j.1748-1716.1980.tb06530.x. [DOI] [PubMed] [Google Scholar]
  28. Taraskevich P. S., Douglas W. W. Catecholamines of supposed inhibitory hypophysiotrophic function suppress action potentials in prolactin cells. Nature. 1978 Dec 21;276(5690):832–834. doi: 10.1038/276832a0. [DOI] [PubMed] [Google Scholar]
  29. Taraskevich P. S., Douglas W. W. Electrical behaviour in a line of anterior pituitary cells (GH cells) and the influence of the hypothalamic peptide, thyrotrophin releasing factor. Neuroscience. 1980;5(2):421–431. doi: 10.1016/0306-4522(80)90117-7. [DOI] [PubMed] [Google Scholar]
  30. Thorner M. O., Hackett J. T., Murad F., MacLeod R. M. Calcium rather than cyclic AMP as the physiological intracellular regulator of prolactin release. Neuroendocrinology. 1980 Dec;31(6):390–402. doi: 10.1159/000123109. [DOI] [PubMed] [Google Scholar]
  31. Zeytin F. N., Gick G. G., Brazeau P., Ling N., McLaughlin M., Bancroft C. Growth hormone (GH)-releasing factor does not regulate GH release or GH mRNA levels in GH3 cells. Endocrinology. 1984 Jun;114(6):2054–2059. doi: 10.1210/endo-114-6-2054. [DOI] [PubMed] [Google Scholar]

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

RESOURCES