Functional expression of transient receptor potential melastatin- and vanilloid-related channels in pulmonary arterial and aortic smooth muscle

Transient receptor potential melastatin- (TRPM) and vanilloid-related (TRPV) channels are nonselective cation channels pertinent to diverse physiological functions. Multiple TRPM and TRPV channel subtypes have been identified and cloned in different tissues. However, their information in vascular tissue is scant. In this study, we sought to identify TRPM and TRPV channel subtypes expressed in rat deendothelialized intralobar pulmonary arteries (PAs) and aorta. With RT-PCR, mRNA of TRPM2, TRPM3, TRPM4, TRPM7, and TRPM8 of TRPM family and TRPV1, TRPV2, TRPV3, and TRPV4 of TRPV family were detected in both PAs and aorta. Quantitative real-time RT-PCR showed that TRPM8 and TRPV4 were the most abundantly expressed TRPM and TRPV subtypes, respectively. Moreover, Western blot analysis verified expression of TRPM2, TRPM8, TRPV1, and TRPV4 proteins in both types of vascular tissue. To examine the functional activities of these channels, we monitored intracellular Ca ²⁺ transients ([Ca ²⁺] _i) in pulmonary arterial smooth muscle cells (PASMCs) and aortic smooth muscle cells (ASMCs). The TRPM8 agonist menthol (300 μM) and the TRPV4 agonist 4α-phorbol 12,13-didecanoate (1 μM) evoked significant increases in [Ca ²⁺] _i in PASMCs and ASMCs. These Ca ²⁺ responses were abolished in the absence of extracellular Ca ²⁺ or the presence of 300 μM Ni ²⁺ but were unaffected by 1 μM nifedipine, suggesting Ca ²⁺ influx via nonselective cation channels. Hence, for the first time, our results indicate that multiple functional TRPM and TRPV channels are coexpressed in rat intralobar PAs and aorta. These novel Ca ²⁺ entry pathways may play important roles in the regulation of pulmonary and systemic circulation.