POSSIBLE INTERACTION OF ALPHA-1-ADRENERGIC RECEPTOR WITH PERTUSSIS-TOXIN-SENSITIVE GUANINE-NUCLEOTIDE-BINDING REGULATORY PROTEINS (G-PROTEINS) RESPONSIBLE FOR PHOSPHOLIPASE-C ACTIVATION IN RAT-LIVER PLASMA-MEMBRANES

Islet‐activating protein (IAP; pertussis toxin) was employed to test the hypothesis that IAP‐sensitive GTP‐binding regulatory proteins (G proteins) are coupled with α1‐adrenergic receptor in rat liver plasma membranes. The high‐affinity state of the binding of α2‐adrenergic agonist, which is known to be coupled with IAP‐sensitive G protein, was abolished in IAP‐treated plasma membranes. IAP treatment of plasma membranes could also diminish the high‐affinity state of the α1‐adrenergic receptor for the agonist. Restoration of the high‐affinity state of the α1‐adrenergic receptor for the agonist occurred on reconstitution of the bovine brain IAP‐sensitive G proteins. The α1‐adrenergic receptor agonist stimulated inositol triphosphate (InsP3) production from [3H]inositollabeled liver plasma membranes in a concentration‐dependent manner. IAP treatment also decreased α1‐adrenergic‐agonist‐induced InsP3 production but not completely. From these results, we concluded that there is a possibility that both IAP‐sensitive and IAP‐insensitive G proteins were involved in α1‐adrenergic‐receptor‐stimulated phospholipase C activation in rat liver plasma membranes. Copyright © 1990, Wiley Blackwell. All rights reserved