[Decreased amplitude of [Ca²âº]i elevation induced by menthol in pulmonary arterial smooth muscle cells of pulmonary hypertensive rats].

The study was designed to explore the alteration of intracellular calcium concentration ([Ca²âº]i), induced by transient receptor potential melastatin 8 (TRPM8) channel-specific agonist menthol, in pulmonary arterial smooth muscle cells (PASMCs) between control and pulmonary hypertensive (PH) rats. PH rat models were established by means of chronic hypoxia (CH) and monocrotaline (MCT) injection, respectively. PASMCs from control and PH rats were cultured. The change of [Ca²âº]i in PASMCs induced by menthol, and the effect of TRPM8 channel-specific antagonist BCTC on the change of [Ca²âº]i, were observed. Cellular localization of TRPM8 was examined by using immunohistochemistry. Results showed that menthol increased [Ca²âº]i in the control PASMCs both in Ca²âº -normal and Ca²âº - free Tyrode's solutions, and at the same time BCTC could inhibit these two kinds of elevations. Compared with the control group, elevations of [Ca²âº]i were decreased notably in CH- and MCT-pretreated PASMCs superfused with 2 mmol/L Ca²âº - or 0 Ca²âº -Tyrode's solutions. Immunohistochemical localization experiments showed that the whole PASMCs were dyed brown except for the nucleus. This study verified that TRPM8 exists both in membrane and sarcoplasmic reticulum of PASMCs. In addition, CH- and MCT-pretreatment could independently down-regulate the Ca²âº influx and Ca²âº release mediated by TRPM8 channel.

Down-regulation of TRPM8 in pulmonary arteries of pulmonary hypertensive rats.

BACKGROUND: Pulmonary hypertension (PH) is characterized by profound vascular remodeling and alterations in Ca(2+) homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Multiple transient receptor potential melastatin-related (TRPM) subtypes have been identified in vascular tissue. However, the changes in the expression and function of TRPM channels in pulmonary hypertension have not been characterized in detail. METHODS: We examined the expression of TRPM channels and characterized the functions of the altered TRPM channels in two widely used rat models of chronic hypoxia (CH)- and monocrotaline (MCT)-induced PH. RESULTS: CH-exposed and MCT-treated rats developed severe PH and right ventricular hypertrophy, with a significant decrease in TRPM8 mRNA and protein expression in pulmonary arteries (PAs). The downregulation of TRPM8 was associated with significant reduction in menthol-induced cation-influx. Time-profiles showed that TRPM8 down-regulation occurred prior to the increase of right ventricular systolic pressure (RVSP) and right ventricular mass index (RVMI) in CH-exposed rats, but these changes were delayed in MCT-treated rats. The TRPM8 agonist menthol induced vasorelaxation in phenylephrine-precontracted PAs, and the vasorelaxing effects were significantly attenuated in PAs of both PH rat models, consistent with decreased TRPM8 expression. CONCLUSION: Downregulation of TRPM8 may contribute to the enhanced vasoreactivity in PH.