Dopaminergic regulation of GABA release from the intact goldfish retina.
The rate of release of [3H]GABA from intact goldfish retinas was studied using a modified superfusion technique. Small, significant increases in the rate of GABA release were observed when the retinas were exposed to dopamine (DA) (100-1000 microM); however, when free Ca2+ was removed from the medium, the basal rate of GABA release was increased and DA became inhibitory. Forskolin, a non-specific stimulator of adenylate cyclase in intact cells, also inhibited GABA release in the absence of Ca2+. There was no significant effect of forskolin in the presence of Ca2+; however, (+)-butaclamol, a dopamine antagonist, increased basal GABA release under these conditions. L-glutamic acid (L-Glu) (1-10 mM) causes up to a 10-fold increase in GABA release. In the presence of Ca2+, DA did not significantly alter the effects of L-Glu; however, in the absence of Ca2+ a significant inhibition of the effects of L-Glu by DA was observed. Forskolin, on the other hand, inhibited the effects of L-Glu both in the presence and absence of Ca2+. Finally, EGTA (0.3-1 mM) produced a large release of GABA: this release was inhibited by DA, forskolin, theophylline, and 8-bromo cyclic AMP. These results suggest a model wherein DA stimulates Ca2+-dependent GABA release from one site and inhibits Ca2+-independent GABA release from another site via a cyclic AMP-mediated event.
O'Brien
D R
DR
Dowling
J E
JE
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D003530:Cyprinidae / Q000502:physiology*; D004298:Dopamine / Q000494:pharmacology / Q000502:physiology*; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D006054:Goldfish / Q000502:physiology*; D066298:In Vitro Techniques; D012160:Retina / Q000502:physiology*; D009435:Synaptic Transmission; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D005971:Glutamates; D005576:Colforsin; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D000242:Cyclic AMP; D002118:Calcium; D004298:Dopamine