Stimulation of Ca(2+)-independent exocytosis in rat pituitary gonadotrophs by G-protein

J Physiol. 2000 Jul 1;526 Pt 1(Pt 1):99-108. doi: 10.1111/j.1469-7793.2000.00099.x.

Abstract

We employed the whole-cell recording technique in conjunction with fluorometry to measure cytosolic Ca(2+) concentration ([Ca(2+)](i)) and exocytosis (capacitance measurement) in single, identified rat gonadotrophs. Direct activation of G-protein (via intracellular dialysis of non-hydrolysable analogues of GTP, but not of GDP) triggered a slow rise in capacitance even in the presence of a fast intracellular Ca(2+) chelator. The broad-spectrum kinase inhibitors H7 and staurosporine did not prevent this Ca(2+)-independent exocytosis, ruling out the involvement of the cAMP and PKC pathways. AlF(4)(-), a potent stimulator of heterotrimeric G-proteins, failed to stimulate any exocytosis when the intracellular Ca(2+) store was depleted, implicating the involvement of AlF(4)(-)-insensitive G-protein(s). Maximal stimulation of Ca(2+)-independent exocytosis by GTP analogues did not reduce the number of readily releasable granules that were available subsequently for Ca(2+)-dependent release. The last finding raises the possibility that the G-protein-stimulated Ca(2+)-independent exocytosis may regulate a pool of granules that is distinct from the Ca(2+)-dependent pool.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / pharmacology
  • Aluminum Compounds / pharmacology
  • Animals
  • Calcium / metabolism*
  • Calcium-Transporting ATPases / antagonists & inhibitors
  • Cyclic AMP / metabolism
  • Cytoplasmic Granules / drug effects
  • Cytoplasmic Granules / metabolism
  • Cytosol / metabolism
  • Egtazic Acid / analogs & derivatives*
  • Egtazic Acid / pharmacology
  • Enzyme Inhibitors / pharmacology
  • Exocytosis / drug effects
  • Exocytosis / physiology*
  • Fluorides / pharmacology
  • Fluorometry
  • GTP-Binding Proteins / metabolism*
  • GTP-Binding Proteins / pharmacology
  • Guanosine 5'-O-(3-Thiotriphosphate) / pharmacology
  • Guanylyl Imidodiphosphate / pharmacology
  • Male
  • Patch-Clamp Techniques
  • Photolysis
  • Pituitary Gland, Anterior / cytology
  • Pituitary Gland, Anterior / drug effects
  • Pituitary Gland, Anterior / metabolism*
  • Protein Kinase C / antagonists & inhibitors
  • Rats
  • Staurosporine / pharmacology

Substances

  • Aluminum Compounds
  • Enzyme Inhibitors
  • tetrafluoroaluminate
  • Guanylyl Imidodiphosphate
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Egtazic Acid
  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine
  • Cyclic AMP
  • Protein Kinase C
  • GTP-Binding Proteins
  • Calcium-Transporting ATPases
  • Staurosporine
  • 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
  • Fluorides
  • Calcium