Interactions between Ca(2+)-mobilizing receptors and their G proteins in hepatocytes.
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.
Dasso
L L
LL
Department of Pharmacology, Cambridge University, Cambridge, UK.
Taylor
C W
CW
D000595:Amino Acid Sequence; D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010656:Phenylephrine / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011945:Receptors, Angiotensin / Q000378:metabolism*; D017483:Receptors, Vasopressin / Q000378:metabolism*; D015398:Signal Transduction
D010455:Peptides; D011941:Receptors, Adrenergic; D011945:Receptors, Angiotensin; D017483:Receptors, Vasopressin; D000804:Angiotensin II; D001127:Arginine Vasopressin; D010656:Phenylephrine; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D002118:Calcium