Local Ca2+ release from internal stores controls exocytosis in pituitary gonadotrophs

Neuron. 1997 Jan;18(1):121-32. doi: 10.1016/s0896-6273(01)80051-9.

Abstract

Exocytosis and the cell-averaged cytosolic [Ca2+], [Ca2+]i, were tracked in single gonadotrophs. Cells released 100 granules/s at 1 microM = [Ca2+]i when gonadotropin-releasing hormone (GnRH) activated IP3-mediated Ca2+ release from internal stores, but only 1 granule/s when [Ca2+]i was raised uniformly to 1 microM by other means. Strong exocytosis was then seen only at higher [Ca2+]i (half-maximal at 16 microM). Parallel second messengers did not contribute to GnRH-induced exocytosis, because IP3 alone was as effective as GnRH, and because even GnRH failed to trigger rapid exocytosis when the [Ca2+]i rise was blunted by EGTA. When [Ca2+]i was released from stores, exocytosis depended on [Ca2+]i rising rapidly, as if governed by Ca2+ flux into the cytosol. We suggest that IP3 releases Ca2+ selectively from subsurface cisternae, raising [Ca2+] near exocytic sites 5-fold above the cell average.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetates / pharmacology
  • Animals
  • Calcium / metabolism*
  • Chelating Agents / pharmacology
  • Cytoplasmic Granules / drug effects
  • Cytoplasmic Granules / metabolism*
  • Cytoplasmic Granules / ultrastructure
  • Cytosol / metabolism
  • Egtazic Acid / pharmacology
  • Ethylenediamines / pharmacology
  • Exocytosis*
  • Gonadotropin-Releasing Hormone / pharmacology*
  • In Vitro Techniques
  • Inositol 1,4,5-Trisphosphate / pharmacology*
  • Kinetics
  • Membrane Potentials
  • Patch-Clamp Techniques
  • Photolysis
  • Pituitary Gland, Anterior / drug effects
  • Pituitary Gland, Anterior / physiology*
  • Pituitary Gland, Anterior / ultrastructure
  • Rats
  • Rats, Sprague-Dawley
  • Time Factors

Substances

  • Acetates
  • Chelating Agents
  • Ethylenediamines
  • DM-nitrophen
  • Gonadotropin-Releasing Hormone
  • Egtazic Acid
  • Inositol 1,4,5-Trisphosphate
  • Calcium