INTERACTIONS BETWEEN CA2-MOBILIZING RECEPTORS AND THEIR G-PROTEINS INHEPATOCYTES()

In hepatocytes, different receptors that share an ability to stimulate inositol 1,4,5-trisphosphate formation by activating guanine nucleoti de-binding proteins (G proteins) evoke Ca2+ signals that are character istic of the receptor that evoked them. High affinity, guanine nucleot ide-sensitive binding of agonists to their receptors provides a conven ient means of assessing receptor-G protein interactions. We used these methods to examine the extent to which different Ca2+-mobilizing rece ptors share G protein pools. Although our earlier results (Dasso, L. L . T., and Taylor, C. W. (1992) Mol. Pharmacol. 42, 453-457) showed tha t activated V-1-vasopressin receptors prevented alpha(1)-adrenorecepto rs from associating with G proteins, our present results show that nei ther alpha(1)-adrenergic agonists nor angiotensin II influences the in teraction between V-1 receptors and their G proteins, This asymmetric scavenging of G proteins by alpha(1)-adrenoreceptors and V-1 receptors is not a consequence of there being more of the latter and may result either from V-1 receptors binding more tightly to G proteins or from their ability to interact with a second G protein pool. We speculate t hat the different interactions among V-1 receptors, alpha(1)-adrenorec eptors, and their G proteins contribute to the differently shaped Ca2 spikes evoked by these receptors.