Short applications of gamma-aminobutyric acid increase intracellular calcium concentrations in single identified rat lactotrophs.
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.
Lorsignol
A
A
Laboratoire de Neurophysiologie, CNRS URA 1200, Université de Bordeaux II, France.
Taupignon
A
A
Dufy
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002336:Carnosine / Q000031:analogs & derivatives / Q000494:pharmacology; D002998:Clonazepam / Q000494:pharmacology; D005260:Female; D058787:GABA-A Receptor Antagonists; D007150:Immunohistochemistry; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009118:Muscimol / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; D009118:Muscimol; C005038:homocarnosine; D005680:gamma-Aminobutyric Acid; D002998:Clonazepam; D002336:Carnosine; D002118:Calcium