Possible interaction of α1‐adrenergic receptor with pertussis‐toxin‐sensitive guanine‐nucleotide‐binding regulatory proteins (G proteins) responsible for phospholipase C activation in rat liver plasma membranes

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Abstract
Islet-activating protein (IAP; pertussis toxin) was employed to test the hypothesis that IAP-sensitive GTP-binding regulatory proteins (G proteins) are coupled with .alpha.1-adrenergic receptor in rat liver plasma membranes. The high-affinity state of the binding of .alpha.2-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 .alpha.1-adrenergic receptor for the agonist. Restoration of the high-affinity state of the .alpha.1-adrenergic receptor for the agonist occurred on reconstitution of the bovine brain IAP-sensitive G proteins. The .alpha.1-adrenergic receptor agonist stimulated inositol triphosphate (InsP3) production from [3H]inositol-labeled liver plasma membranes in a concentration-dependent manner. IAP treatment also decreased .alpha.1-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 .alpha.1-adrenergic-receptor-stimulated phospholipase C activation in rat liver plasma membranes.

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