Short applications of gamma-aminobutyric acid increase intracellular calcium concentrations in single identified rat lactotrophs

Neuroendocrinology. 1994 Oct;60(4):389-99. doi: 10.1159/000126773.

Abstract

We have investigated the direct effect of GABA receptor agonists on the cytosolic free calcium concentration ([Ca2+]i) and the membrane potential of rat lactotrophs in primary culture. [Ca2+]i was recorded in single identified lactotrophs by dual emission microspectrofluorimetry using indo-1 as intracellular fluorescent calcium probe. Whole cell and perforated patch-clamp were performed. A short application of GABA (10(-5) M, 10 s) induced a marked transient [Ca2+]i increase in 66% of lactotrophs, which could be readily mimicked by muscimol (10(-5) M). By contrast, neither L-homocarnosine (10(-3) M) nor baclofen (10(-5) M), a GABAB agonist, had any effect on [Ca2+]i. The GABA-induced [Ca2+]i increase was antagonized by picrotoxin (10(-5) M), bicuculline methiodide (10(-5) M) and strychnine (10(-4) M), demonstrating GABAA receptor specificity. Furthermore, clonazepan (1.5 x 10(-4) M) could potentiate the GABA effect on [Ca2+]i. The [Ca2+]i increase disappeared in the absence of Ca2+ in the extracellular medium or in the presence of Ca2+ channel blockers (cadmium, PN 200-110). GABA and muscimol depolarized the membrane potential with a concomitant fall in cell input resistance, thus suggesting, as in other cell types, the opening of receptor-operated chloride channels. When Ca2+ entry was prevented by the use of cadmium (500 x 10(-6) M), GABA still elicited membrane depolarization but did not raise [Ca2+]i. Our results suggest that a short application of GABA leads to Ca2+ entry through voltage-gated Ca2+ channels in single lactotrophs. This Ca2+ influx is due to depolarization of the prolactin cell.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Carnosine / analogs & derivatives
  • Carnosine / pharmacology
  • Clonazepam / pharmacology
  • Female
  • GABA-A Receptor Antagonists
  • Immunohistochemistry
  • Ion Channel Gating / drug effects
  • Membrane Potentials / drug effects
  • Muscimol / pharmacology
  • Patch-Clamp Techniques
  • Pituitary Gland, Anterior / drug effects
  • Pituitary Gland, Anterior / metabolism*
  • Radioimmunoassay
  • Rats
  • Rats, Wistar
  • Receptors, GABA-A / metabolism
  • gamma-Aminobutyric Acid / pharmacology*

Substances

  • Calcium Channel Blockers
  • GABA-A Receptor Antagonists
  • Receptors, GABA-A
  • Muscimol
  • homocarnosine
  • gamma-Aminobutyric Acid
  • Clonazepam
  • Carnosine
  • Calcium