J. Biol. Chem., Vol. 269, Issue 12, 8647-8652, Mar, 1994
Interactions between Ca(2+)-mobilizing receptors and their G proteins in hepatocytes
LL Dasso and CW Taylor
Department of Pharmacology, Cambridge University, Cambridge, UK.
In hepatocytes, different receptors that share an ability to stimulate
inositol 1,4,5-trisphosphate formation by activating guanine nucleotide-
binding proteins (G proteins) evoke Ca2+ signals that are characteristic of
the receptor that evoked them. High affinity, guanine nucleotide-sensitive
binding of agonists to their receptors provides a convenient means of
assessing receptor-G protein interactions. We used these methods to examine
the extent to which different Ca(2+)- mobilizing receptors share G protein
pools. Although our earlier results (Dasso, L. L. T., and Taylor, C.W.
(1992) Mol. Pharmacol. 42, 453-457) showed that activated V1-vasopressin
receptors prevented alpha 1-adrenoreceptors from associating with G
proteins, our present results show that neither alpha 1-adrenergic agonists
nor angiotensin II influences the interaction between V1 receptors and
their G proteins. This asymmetric scavenging of G proteins by alpha
1-adrenoreceptors and V1 receptors is not a consequence of there being more
of the latter and may result either from V1 receptors binding more tightly
to G proteins or from their ability to interact with a second G protein
pool. We speculate that the different interactions among V1 receptors,
alpha 1- adrenoreceptors, and their G proteins contribute to the
differently shaped Ca2+ spikes evoked by these receptors.
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