Dual action of GABAA receptors on the secretory process of melanotrophs of Xenopus laevis.
The effects of GABAa receptor activation on the secretion of alpha-melanocyte-stimulating hormone (alpha-MSH) from the superfused pars intermedia of the amphibian Xenopus laevis were examined. The GABAa receptor agonist isoguvacine inhibited secretion of alpha-MSH from the pars intermedia, an action completely antagonized by the chloride channel blocker picrotoxin. Isoguvacine stimulated secretion from picrotoxin-treated tissue. Both effects were blocked by the GABAA receptor antagonist bicuculline, indicating that it is a specific action via the GABAA receptor. We conclude that, besides the inhibitory chloride channel, there is a stimulatory signaling property associated with the GABAA receptor. Isoguvacine stimulated the production of c-AMP, an action that was not blocked by picrotoxin. This suggests that the stimulatory mechanism of the GABAA receptor involves, directly or indirectly, the generation of c-AMP.
Jenks
B G
BG
Department of Animal Physiology, University of Nijmegen, The Netherlands.
de Koning
H P
HP
Valentijn
K
K
Roubos
E W
EW
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D007539:Isonicotinic Acids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010852:Picrotoxin / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000502:physiology*; D014982:Xenopus laevis; D000521:alpha-MSH / Q000378:metabolism*
D001640:Bicuculline; D000242:Cyclic AMP; D007539:Isonicotinic Acids; D010852:Picrotoxin; D011963:Receptors, GABA-A; D000521:alpha-MSH; C015300:isoguvacine