Skip to main content
PMC home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1997 Nov 1;504(Pt 3):705–719. doi: 10.1111/j.1469-7793.1997.705bd.x

Modulation of stimulus-secretion coupling in single rat gonadotrophs.

P Thomas 1, D W Waring 1
PMCID: PMC1159972  PMID: 9401976

Abstract

1. Exocytosis and intracellular [Ca2+] were determined simultaneously in single anterior pituitary gonadotrophs from ovariectomized female rats. Dispersed cells were cultured for 2-4 days with or without 0.2 nM oestradiol-17 beta (E2) before use. Cells were stimulated with either gonadotrophin releasing hormone (GnRH) or by membrane depolarization. Exocytosis was determined from the change in membrane capacitance (Cm) using the perforated-patch whole-cell recording technique. Intracellular [Ca2+] was measured using fura-2 fluorescence. 2. The exocytotic response to 1 nM GnRH was characterized by a wide spectrum of responses, ranging from exocytotic bursts to relatively slow, graded increases that were dependent on the evoked intracellular Ca2+ pattern. A kinetic model is presented that incorporates the observed steep dependence of exocytosis on measured intracellular [Ca2+]; simulated exocytosis reasonably approximated observed exocytotic responses, both kinetically and quantitatively. The model also suggests that the modulatory effects of E2 are brought about either by a change in the Ca2+ sensitivity of exocytosis or by a preferential clustering of docked-secretory granules close to sites of Ca2+ release. The results suggest that in gonadotrophs an oscillatory Ca2+ signal is sensed by the exocytotic apparatus in a modified form of digital encoding. 3. Exocytosis in E2-treated cells was 3-fold greater than in non-treated cells for GnRH-evoked secretion, and 38% greater for depolarization; however, there was no effect of E2 on the intracellular Ca2+ response to either stimulus. The results show that maximum expression of the effect of E2 on exocytosis requires activation of GnRH-dependent pathways.

Full text

PDF
717

Selected References

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

  1. Almers W., Neher E. The Ca signal from fura-2 loaded mast cells depends strongly on the method of dye-loading. FEBS Lett. 1985 Nov 11;192(1):13–18. doi: 10.1016/0014-5793(85)80033-8. [DOI] [PubMed] [Google Scholar]
  2. Artalejo C. R., Elhamdani A., Palfrey H. C. Calmodulin is the divalent cation receptor for rapid endocytosis, but not exocytosis, in adrenal chromaffin cells. Neuron. 1996 Jan;16(1):195–205. doi: 10.1016/s0896-6273(00)80036-7. [DOI] [PubMed] [Google Scholar]
  3. Artalejo C. R., Henley J. R., McNiven M. A., Palfrey H. C. Rapid endocytosis coupled to exocytosis in adrenal chromaffin cells involves Ca2+, GTP, and dynamin but not clathrin. Proc Natl Acad Sci U S A. 1995 Aug 29;92(18):8328–8332. doi: 10.1073/pnas.92.18.8328. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Augustine G. J., Neher E. Calcium requirements for secretion in bovine chromaffin cells. J Physiol. 1992 May;450:247–271. doi: 10.1113/jphysiol.1992.sp019126. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Bittner M. A., Holz R. W. Protein kinase C and clostridial neurotoxins affect discrete and related steps in the secretory pathway. Cell Mol Neurobiol. 1993 Dec;13(6):649–664. doi: 10.1007/BF00711564. [DOI] [PubMed] [Google Scholar]
  6. Drouva S. V., Gorenne I., Laplante E., Rérat E., Enjalbert A., Kordon C. Estradiol modulates protein kinase C activity in the rat pituitary in vivo and in vitro. Endocrinology. 1990 Jan;126(1):536–544. doi: 10.1210/endo-126-1-536. [DOI] [PubMed] [Google Scholar]
  7. Emons G., Hoffmann H. G., Brack C., Ortmann O., Sturm R., Ball P., Knuppen R. Modulation of gonadotropin-releasing hormone receptor concentration in cultured female rat pituitary cells by estradiol treatment. J Steroid Biochem. 1988 Nov;31(5):751–756. doi: 10.1016/0022-4731(88)90282-8. [DOI] [PubMed] [Google Scholar]
  8. Fidler N., Fernandez J. M. Phase tracking: an improved phase detection technique for cell membrane capacitance measurements. Biophys J. 1989 Dec;56(6):1153–1162. doi: 10.1016/S0006-3495(89)82762-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Gillis K. D., Mossner R., Neher E. Protein kinase C enhances exocytosis from chromaffin cells by increasing the size of the readily releasable pool of secretory granules. Neuron. 1996 Jun;16(6):1209–1220. doi: 10.1016/s0896-6273(00)80147-6. [DOI] [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. Heinemann C., von Rüden L., Chow R. H., Neher E. A two-step model of secretion control in neuroendocrine cells. Pflugers Arch. 1993 Jul;424(2):105–112. doi: 10.1007/BF00374600. [DOI] [PubMed] [Google Scholar]
  12. Horwitz K. B., McGuire W. L. Nuclear mechanisms of estrogen action. Effects of estradiol and anti-estrogens on estrogen receptors and nuclear receptor processing. J Biol Chem. 1978 Nov 25;253(22):8185–8191. [PubMed] [Google Scholar]
  13. Knight D. E., Baker P. F. The phorbol ester TPA increases the affinity of exocytosis for calcium in 'leaky' adrenal medullary cells. FEBS Lett. 1983 Aug 22;160(1-2):98–100. doi: 10.1016/0014-5793(83)80944-2. [DOI] [PubMed] [Google Scholar]
  14. Law G. J., Pachter J. A., Dannies P. S. Ca2+ transients induced by thyrotropin-releasing hormone rapidly lose their ability to cause release of prolactin. Mol Endocrinol. 1989 Mar;3(3):539–546. doi: 10.1210/mend-3-3-539. [DOI] [PubMed] [Google Scholar]
  15. Leong D. A., Thorner M. O. A potential code of luteinizing hormone-releasing hormone-induced calcium ion responses in the regulation of luteinizing hormone secretion among individual gonadotropes. J Biol Chem. 1991 May 15;266(14):9016–9022. [PubMed] [Google Scholar]
  16. Meyer T., Stryer L. Calcium spiking. Annu Rev Biophys Biophys Chem. 1991;20:153–174. doi: 10.1146/annurev.bb.20.060191.001101. [DOI] [PubMed] [Google Scholar]
  17. Ortmann O., Stojilković S. S., Cesnjaj M., Emons G., Catt K. J. Modulation of cytoplasmic calcium signaling in rat pituitary gonadotrophs by estradiol and progesterone. Endocrinology. 1992 Sep;131(3):1565–1567. doi: 10.1210/endo.131.3.1505483. [DOI] [PubMed] [Google Scholar]
  18. Ortmann O., Tilse B., Emons G. Modulatory actions of estradiol and progesterone on phorbol ester-stimulated LH secretion from cultured rat pituitary cells. J Steroid Biochem Mol Biol. 1992 Dec;43(7):619–627. doi: 10.1016/0960-0760(92)90286-r. [DOI] [PubMed] [Google Scholar]
  19. Parsons T. D., Coorssen J. R., Horstmann H., Almers W. Docked granules, the exocytic burst, and the need for ATP hydrolysis in endocrine cells. Neuron. 1995 Nov;15(5):1085–1096. doi: 10.1016/0896-6273(95)90097-7. [DOI] [PubMed] [Google Scholar]
  20. Samli M. H., Geschwind I. I. Some effects of energy-transfer inhibitors and of Ca++-free or K+-enhanced media on the release of luteinizing hormone (LH) from the rat pituitary gland in vitro. Endocrinology. 1968 Feb;82(2):225–231. doi: 10.1210/endo-82-2-225. [DOI] [PubMed] [Google Scholar]
  21. Smith G. D. Analytical steady-state solution to the rapid buffering approximation near an open Ca2+ channel. Biophys J. 1996 Dec;71(6):3064–3072. doi: 10.1016/S0006-3495(96)79500-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Smith G. D., Wagner J., Keizer J. Validity of the rapid buffering approximation near a point source of calcium ions. Biophys J. 1996 Jun;70(6):2527–2539. doi: 10.1016/S0006-3495(96)79824-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Stojilkovic S. S., Catt K. J. Expression and signal transduction pathways of gonadotropin-releasing hormone receptors. Recent Prog Horm Res. 1995;50:161–205. doi: 10.1016/b978-0-12-571150-0.50012-3. [DOI] [PubMed] [Google Scholar]
  24. Stojilković S. S., Iida T., Merelli F., Torsello A., Krsmanović L. Z., Catt K. J. Interactions between calcium and protein kinase C in the control of signaling and secretion in pituitary gonadotrophs. J Biol Chem. 1991 Jun 5;266(16):10377–10384. [PubMed] [Google Scholar]
  25. Stutzin A., Stojilković S. S., Catt K. J., Rojas E. Characteristics of two types of calcium channels in rat pituitary gonadotrophs. Am J Physiol. 1989 Nov;257(5 Pt 1):C865–C874. doi: 10.1152/ajpcell.1989.257.5.C865. [DOI] [PubMed] [Google Scholar]
  26. Thomas P., Mellon P. L., Turgeon J., Waring D. W. The L beta T2 clonal gonadotrope: a model for single cell studies of endocrine cell secretion. Endocrinology. 1996 Jul;137(7):2979–2989. doi: 10.1210/endo.137.7.8770922. [DOI] [PubMed] [Google Scholar]
  27. Thomas P., Surprenant A., Almers W. Cytosolic Ca2+, exocytosis, and endocytosis in single melanotrophs of the rat pituitary. Neuron. 1990 Nov;5(5):723–733. doi: 10.1016/0896-6273(90)90226-6. [DOI] [PubMed] [Google Scholar]
  28. Thomas P., Wong J. G., Lee A. K., Almers W. A low affinity Ca2+ receptor controls the final steps in peptide secretion from pituitary melanotrophs. Neuron. 1993 Jul;11(1):93–104. doi: 10.1016/0896-6273(93)90274-u. [DOI] [PubMed] [Google Scholar]
  29. Tomić M., Cesnajaj M., Catt K. J., Stojilkovic S. S. Developmental and physiological aspects of Ca2+ signaling in agonist-stimulated pituitary gonadotrophs. Endocrinology. 1994 Nov;135(5):1762–1771. doi: 10.1210/endo.135.5.7956899. [DOI] [PubMed] [Google Scholar]
  30. Tse A., Tse F. W., Almers W., Hille B. Rhythmic exocytosis stimulated by GnRH-induced calcium oscillations in rat gonadotropes. Science. 1993 Apr 2;260(5104):82–84. doi: 10.1126/science.8385366. [DOI] [PubMed] [Google Scholar]
  31. Tse A., Tse F. W., Hille B. Calcium homeostasis in identified rat gonadotrophs. J Physiol. 1994 Jun 15;477(Pt 3):511–525. doi: 10.1113/jphysiol.1994.sp020212. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Tse F. W., Tse A., Hille B., Horstmann H., Almers W. Local Ca2+ release from internal stores controls exocytosis in pituitary gonadotrophs. Neuron. 1997 Jan;18(1):121–132. doi: 10.1016/s0896-6273(01)80051-9. [DOI] [PubMed] [Google Scholar]
  33. Tsien R. W., Tsien R. Y. Calcium channels, stores, and oscillations. Annu Rev Cell Biol. 1990;6:715–760. doi: 10.1146/annurev.cb.06.110190.003435. [DOI] [PubMed] [Google Scholar]
  34. Turgeon J. L., Waring D. W. Rapid augmentation by progesterone of agonist-stimulated luteinizing hormone secretion by cultured pituitary cells. Endocrinology. 1990 Aug;127(2):773–780. doi: 10.1210/endo-127-2-773. [DOI] [PubMed] [Google Scholar]
  35. von Rüden L., Neher E. A Ca-dependent early step in the release of catecholamines from adrenal chromaffin cells. Science. 1993 Nov 12;262(5136):1061–1065. doi: 10.1126/science.8235626. [DOI] [PubMed] [Google Scholar]

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

RESOURCES