α1-Adrenergic Receptor Stimulation Causes Arachidonic Acid Release through Pertussis Toxin-Sensitive GTP-Binding Protein and JNK Activation in Rabbit Aortic Smooth Muscle Cells

Abstract

In the present study, we investigated the mechanism of phenylephrine (α1-adrenergic receptor agonist)-induced arachidonic acid release in Japanese white rabbit aortic smooth muscle cells (SMC). When introduced into permeabilized smooth muscle cells, guanosine S-[γ-thio] triphosphate (GTPγS), which activates GTP-binding proteins (G proteins), stimulated arachidonic acid (AA) release. Neomycin, an inhibitor of phospho-inositide (PI) turnover, was almost without effect on GTP[γS] stimulated AA release. In addition, pertussis toxin (PT) partially inhibited phenylephrine-stimulated AA release, suggesting that IAP (Islet activating protein)-sensitive G proteins mediate this process. Phenylephrine-stimulated AA release was also inhibited by decreased extracellular calcium and aristolochic acid, suggesting a role for a phospholipase A2(PLA2). Next PLA2is reported to be a substrate for mitogen-activated protein (MAP) kinase. We examined the effect of phenylephrine on MAP kinase and c-jun N-terminal kinase (JNK) phosphorylation. Phenylephrine didn't induce phosphorylation of MAP kinase, but did induce phosphorylation of JNK. In addition, cells which were pretreated with PT inhibited the phosphorylation of JNK. These results suggest that IAP-sensitive G protein is involved in the coupling between α1-adrenergic receptor (AR) and PLA2in cultured rabbit aortic SMCs, and that the α1-AR-induced AA release is mediated by JNK.