Skip to main content
PMC home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1990 Jun;425:29–42. doi: 10.1113/jphysiol.1990.sp018090

Two types of voltage-dependent calcium current in rat somatotrophs are reduced by somatostatin.

C Chen 1, J Zhang 1, J D Vincent 1, J M Israel 1
PMCID: PMC1189835  PMID: 1976802

Abstract

1. Somatotrophs were obtained from rat pituitary glands after dissociation, separation and enrichment on a continuous gradient of bovine serum albumin at unit gravity. Somatotrophs were enriched up to 85% in the heavy fractions (F8 and F9). 2. After identification by reverse hemolytic plaque assay, patch-clamp recording in the whole-cell mode was performed on somatotrophs. 3. Under voltage-clamp conditions, two types of Ca2+ currents were recorded. From a holding potential of -70 mV, depolarizing voltage steps to potentials more positive than -50 mV activated a current which rapidly inactivated and which was very sensitive to Ni2+ but not to Cd2+. This current corresponds to T-type current. Depolarizing steps to potentials more positive than -30 mV from a holding potential of -40 mV triggered a current which slowly inactivated and which was very sensitive to Cd2+ but not to Ni2+. This current corresponds to L-type current. 4. Application of somatostatin to the bath solution (10 nM) markedly reduced the amplitudes of both T- and L-type currents. Somatostatin decreased the conductance of L-type current without modifying its time- and voltage-dependent inactivation but its activation was not affected. However, somatostatin decreased the conductance of T-type currents, and also accelerated its time-dependent inactivation. Half-inactivation voltage of T-type current was shifted from -52 to -63 mV by somatostatin but no change was obtained in the current activation curve. 5. All these modifications in Ca2+ currents were abolished by a pre-treatment of the cultures with pertussis toxin (100 ng/ml, for 10 h). This pre-treatment also blocked the inhibitory effect of somatostatin on high-K(+)-stimulated growth hormone release. 6. Our results show that somatostatin acts on somatotrophs by attenuating the voltage-dependent Ca2+ currents. These effects may contribute to a somatostatin-induced reduction in [Ca2+]i and the subsequent decline in growth hormone release.

Full text

PDF
32

Selected References

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

  1. Bokoch G. M., Katada T., Northup J. K., Ui M., Gilman A. G. Purification and properties of the inhibitory guanine nucleotide-binding regulatory component of adenylate cyclase. J Biol Chem. 1984 Mar 25;259(6):3560–3567. [PubMed] [Google Scholar]
  2. Chen C., Israel J. M., Vincent J. D. Electrophysiological responses of rat pituitary cells in somatotroph-enriched primary culture to human growth-hormone releasing factor. Neuroendocrinology. 1989 Dec;50(6):679–687. doi: 10.1159/000125299. [DOI] [PubMed] [Google Scholar]
  3. Chen C., Israel J. M., Vincent J. D. Electrophysiological responses to somatostatin of rat hypophysial cells in somatotroph-enriched primary cultures. J Physiol. 1989 Jan;408:493–510. doi: 10.1113/jphysiol.1989.sp017472. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Chen C., Zhang J., Vincent J. D., Israel J. M. Sodium and calcium currents in action potentials of rat somatotrophs: their possible functions in growth hormone secretion. Life Sci. 1990;46(14):983–989. doi: 10.1016/0024-3205(90)90021-i. [DOI] [PubMed] [Google Scholar]
  5. Cota G. Calcium channel currents in pars intermedia cells of the rat pituitary gland. Kinetic properties and washout during intracellular dialysis. J Gen Physiol. 1986 Jul;88(1):83–105. doi: 10.1085/jgp.88.1.83. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Dorflinger L. J., Schonbrunn A. Somatostatin inhibits basal and vasoactive intestinal peptide-stimulated hormone release by different mechanisms in GH pituitary cells. Endocrinology. 1983 Nov;113(5):1551–1558. doi: 10.1210/endo-113-5-1551. [DOI] [PubMed] [Google Scholar]
  7. Epelbaum J., Enjalbert A., Krantic S., Musset F., Bertrand P., Rasolonjanahary R., Shu C., Kordon C. Somatostatin receptors on pituitary somatotrophs, thyrotrophs, and lactotrophs: pharmacological evidence for loose coupling to adenylate cyclase. Endocrinology. 1987 Dec;121(6):2177–2185. doi: 10.1210/endo-121-6-2177. [DOI] [PubMed] [Google Scholar]
  8. Fox A. P., Nowycky M. C., Tsien R. W. Kinetic and pharmacological properties distinguishing three types of calcium currents in chick sensory neurones. J Physiol. 1987 Dec;394:149–172. doi: 10.1113/jphysiol.1987.sp016864. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Fox A. P., Nowycky M. C., Tsien R. W. Single-channel recordings of three types of calcium channels in chick sensory neurones. J Physiol. 1987 Dec;394:173–200. doi: 10.1113/jphysiol.1987.sp016865. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. 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]
  11. Holl R. W., Thorner M. O., Leong D. A. Intracellular calcium concentration and growth hormone secretion in individual somatotropes: effects of growth hormone-releasing factor and somatostatin. Endocrinology. 1988 Jun;122(6):2927–2932. doi: 10.1210/endo-122-6-2927. [DOI] [PubMed] [Google Scholar]
  12. Ikeda S. R., Schofield G. G. Somatostatin blocks a calcium current in rat sympathetic ganglion neurones. J Physiol. 1989 Feb;409:221–240. doi: 10.1113/jphysiol.1989.sp017494. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Inoue M., Nakajima S., Nakajima Y. Somatostatin induces an inward rectification in rat locus coeruleus neurones through a pertussis toxin-sensitive mechanism. J Physiol. 1988 Dec;407:177–198. doi: 10.1113/jphysiol.1988.sp017409. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Lewis D. L., Weight F. F., Luini A. A guanine nucleotide-binding protein mediates the inhibition of voltage-dependent calcium current by somatostatin in a pituitary cell line. Proc Natl Acad Sci U S A. 1986 Dec;83(23):9035–9039. doi: 10.1073/pnas.83.23.9035. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Mason W. T., Rawlings S. R. Whole-cell recordings of ionic currents in bovine somatotrophs and their involvement in growth hormone secretion. J Physiol. 1988 Nov;405:577–593. doi: 10.1113/jphysiol.1988.sp017349. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. 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]
  17. Mihara S., North R. A., Surprenant A. Somatostatin increases an inwardly rectifying potassium conductance in guinea-pig submucous plexus neurones. J Physiol. 1987 Sep;390:335–355. doi: 10.1113/jphysiol.1987.sp016704. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Mollard P., Vacher P., Dufy B., Barker J. L. Somatostatin blocks Ca2+ action potential activity in prolactin-secreting pituitary tumor cells through coordinate actions on K+ and Ca2+ conductances. Endocrinology. 1988 Aug;123(2):721–732. doi: 10.1210/endo-123-2-721. [DOI] [PubMed] [Google Scholar]
  19. Neill J. D., Frawley L. S. Detection of hormone release from individual cells in mixed populations using a reverse hemolytic plaque assay. Endocrinology. 1983 Mar;112(3):1135–1137. doi: 10.1210/endo-112-3-1135. [DOI] [PubMed] [Google Scholar]
  20. Nowycky M. C., Fox A. P., Tsien R. W. Three types of neuronal calcium channel with different calcium agonist sensitivity. Nature. 1985 Aug 1;316(6027):440–443. doi: 10.1038/316440a0. [DOI] [PubMed] [Google Scholar]
  21. Sheppard M. S., Moor B. C., Kraicer J. Release of growth hormone (GH) from purified somatotrophs: interaction of GH-releasing factor and somatostatin and role of adenosine 3',5'-monophosphate. Endocrinology. 1985 Dec;117(6):2364–2370. doi: 10.1210/endo-117-6-2364. [DOI] [PubMed] [Google Scholar]
  22. Sheppard M. S., Spence J. W., Kraicer J. Release of growth hormone from purified somatotrophs: role of adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate. Endocrinology. 1979 Jul;105(1):261–268. doi: 10.1210/endo-105-1-261. [DOI] [PubMed] [Google Scholar]
  23. Sikdar S. K., Waring D. W., Mason W. T. Voltage activated ionic currents in gonadotrophs of the ovine pars tuberalis. Neurosci Lett. 1986 Oct 30;71(1):95–100. doi: 10.1016/0304-3940(86)90263-6. [DOI] [PubMed] [Google Scholar]
  24. Swandulla D., Armstrong C. M. Calcium channel block by cadmium in chicken sensory neurons. Proc Natl Acad Sci U S A. 1989 Mar;86(5):1736–1740. doi: 10.1073/pnas.86.5.1736. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Tsien R. W., Lipscombe D., Madison D. V., Bley K. R., Fox A. P. Multiple types of neuronal calcium channels and their selective modulation. Trends Neurosci. 1988 Oct;11(10):431–438. doi: 10.1016/0166-2236(88)90194-4. [DOI] [PubMed] [Google Scholar]
  26. Yamashita N., Shibuya N., Ogata E. Hyperpolarization of the membrane potential caused by somatostatin in dissociated human pituitary adenoma cells that secrete growth hormone. Proc Natl Acad Sci U S A. 1986 Aug;83(16):6198–6202. doi: 10.1073/pnas.83.16.6198. [DOI] [PMC free article] [PubMed] [Google Scholar]

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

RESOURCES