Effects of GTP, forskolin, sodium fluoride, serotonin, dopamine, and carbachol on adenylate cyclase in Teleost retina.

Adenylate cyclase activity can be stimulated in goldfish retina by forskolin, GTP, NaF, dopamine and serotonin. Pharmacological characterisation of the dopamine and serotonin responses shows them to be mediated through specific receptors. A synergistic increase in the level of C-AMP is observed following application of forskolin together with NaF, GTP, dopamine, or serotonin. Dopamine and serotonin with or without GTP produce an additive response. When NaF and GTP are both together their combined effect in elevating C-AMP levels in the presence or absence of forskolin is less than additive. These results suggest that forskolin may be interacting with a Gs protein as well as directly stimulating adenylate cyclase. Increases in the level of C-AMP observed following application of forskolin or dopamine are decreased by carbachol in a dose-dependent manner. The carbachol response is blocked by pertussis toxin and is insensitive to the phosphodiesterase inhibitor, IBMX, suggesting an involvement of a Gi protein. Carbachol attenuation of elevated C-AMP levels is inhibited by atropine while pirenzapine has little effect suggesting the presence of a M2-type receptor.