A TRPC-like non-selective cation current activated by α 1-adrenoceptors in rat mesenteric artery smooth muscle cells

Abstract

The TRPC family of non-selective cation channels has been suggested to play a key role in the responses to α 1-adrenoceptor stimulation of vascular smooth muscle. However, there are still very few reports of non-selective cation currents activated by α 1-AR in resistance arteries. Here, we examine the expression of TRPC channels and the currents activated by α 1-adrenoceptors in rat mesenteric resistance artery smooth muscle. Messenger RNA and protein for TRPC1, TRPC3 and TRPC6 were detected within the arteries by RT-PCR and immunoblotting. Endothelial and adventitial layers were found to express the TRPC1, TRPC3 and TRPC6 proteins whereas only TRPC1 and TRPC6 were detected in the arterial smooth muscle by confocal immunofluorescence microscopy. In whole-cell patch-clamp recordings from isolated mesenteric arterial myocytes, an outwardly rectifying non-selective cation current was activated by both the α 1-adrenoceptor agonist, phenylephrine (10 μM), and the diacylglycerol analogue, 1-oleoyl-2-acetyl- sn-glycerol (100 μM). Responses to 1-oleoyl-2-acetyl- sn-glycerol were not blocked, but increased, following inhibition of protein-kinase-C with either bisindolylmaleimide-I (1 μM) or chelerythrine (1 μM). The currents activated by both phenylephrine and 1-oleoyl-2-acetyl- sn-glycerol were inhibited by Gd 3+ (100 μM) but potentiated by flufenamic acid (100 μM). Collectively, these findings demonstrate for the first time the expression of TRPC1 and TRPC6 in rat mesenteric artery smooth muscle and the existence in rat isolated mesenteric arterial myocytes of a TRPC-like non-selective cation current activated by α 1-adrenoceptor stimulation and 1-oleoyl-2-acetyl- sn-glycerol.