TRPV4 Channels Regulate Endothelial Ca Signaling in Rat Maternal Uteroplacental Vasculature

Abstract

An increase in cytosolic Ca2+ ([Ca2+]i) is a key mechanism translating the effects of agonist stimulation of endothelial cells (ECs) into cellular responses. In this study we explored the role of TRPV4 channels in regulating EC Ca2+ signaling in uteroplacental arteries of pregnant rats. The diameters, SMC membrane potential (MP) and [Ca2+]i responses to activation of TRPV4 channels with GSK 1016790A (GSK) were studied using pressurized arteries. ACh- and GSK-induced EC [Ca2+]i responses were characterized in sheets of ECs. The effects of GSK on MP of ECs were tested using perforated patch clamp. RT PCR was performed to quantify mRNA levels of TRPV4 in uterine vasculature. GSK induced an endothelium-mediated vasodilation (78 ± 7 % at 10 nM, n = 8) that was associated with SMC hyperpolarization (by 22 ± 3 mV) or SMC [Ca2+]i reduction. GSK induced EC [Ca2+]i rise of 418 ± 45 nM (n = 4). HC067047 (HC) and TRAM-34, inhibitors of TRPV4 and IK channels, abolished GSK responses. EC hyperpolarization (by 25 ± 6 mV, n = 5) to GSK was reversed by charybdotoxin. ACh-induced vasodilation or elevation of EC [Ca2+]i was reduced by HC by 76 % (n = 4). TRPV4 expression in radial arteries was two-fold higher than in main uterine artery. TRPV4 channels are essential Ca2+ entry pathways in ECs of uteroplacental arteries. They induce IK-dependent hyperpolarization of ECs resulting in EC and SMC hyperpolarization, SMC [Ca2+]i reduction and vasodilation. Downregulation of these channels may contribute to an impaired EC Ca2+ signaling and uterine endothelial dysfunction in complicated pregnancies. Supported by NIH HL088245 (NIG), P01 HL095488 (ADB)