Abstract
Vasopressin (VP) and angiotensin II (AT II) stimulate the production of inositol phosphates (IP) in rat glomerulosa cells. Guanosine 5'-[gamma-thio]triphosphate (GTP[S]), but not VP or AT II, stimulates IP production in a myo-[3H]inositol-prelabelled glomerulosa-cell membrane preparation. In combination with GTP[S], these hormones potentiate the response to GTP[S], indicating the existence of a G-protein involved in the coupling of the VP and AT II receptor with the phospholipase C. ADP-ribosylation with pertussis toxin (IAP) revealed the specific labelling of a single molecule of 41 kDa. No significant inhibition of VP- or AT II-stimulated IP accumulation was detected in intact cells when the whole 41 kDa molecule was endogenously ADP-ribosylated by IAP treatment. On the contrary, when glomerulosa cells were infected with cholera toxin (CT), both the VP- and AT II-stimulated IP accumulations were inhibited in a dose-dependent manner. Yet these effects were partial even at high concentrations of CT, and could not be related to the ADP-ribosylation of 'alpha s' molecules. Similarly, when the cells were infected with 1 microgram of CT/ml, the specific binding of VP and AT II decreased by 50-60%. Such results may signify that the treatment primarily affects the densities of the hormone receptors. When glomerulosa cells were incubated for 15 h in the presence of 10 nM-corticotropin (ACTH), a condition in which the intracellular concentration of cyclic AMP was increased 3-fold, the maximum IP response to 0.1 microM-VP or -AT II was decreased by 50%. When similar experiments were carried out only after a 15 min incubation period with the same concentration of ACTH, the increase in cyclic AMP was more pronounced, but no inhibition of hormone-induced IP accumulation was observed. Altogether, these results may suggest that CT exerts its action on the VP- or AT II-sensitive phospholipase C systems via a prolonged increase in intracellular cyclic AMP.