ABSTRACT
Non-specific TRPM8 agonist menthol was shown to inhibit voltage- and agonist-evoked contractions of the smooth muscle (SM) of rat vas deferens. Here we compared the action of menthol with the action of more specific TRPM8 agonist icilin on depolarization- (60 mM KCl), carbachol-(CCh) and noradrenalin-(Nor)-evoked contractions of the SM strips from the prostatic and epididymal portions of the vas deferens of normal and castrated (60-137 days) rats. Inhibitory action of menthol (100 microM) and icilin (10 microM) on the amplitude of KCl-, CCh- and Nor-induced contractions of normal as well as castrated rats was similar consisting about 50%, despite castration per se strongly potentiated CCh- and Nor-evoked contractions compared to the control animals. In the epididymal portion of the control animals menthol suppressed KC 1- and CCh-evoked contractions by 46 +/- 5% and 32 +/- 3% and icilin by only 14 +/- 4% and 6 +/- 7%, respectively, whilst after castration both compounds became virtually ineffective. Considering that TRPM8 may localize in the sarcolemma and sarcoplasmic reticulum (SR) membrane and that menthol can also block voltage-gated calcium channels (VGCCs), our data indicate that in the prostatic portion TRPM8 modulates contractility by primarily decreasing the SR Ca2+ stores content, whilst in the epididymal one by both decreasing the SR filling and supporting Ca2+ entry. Drop in the circulation androgens as a result of castration changes the menthol- and icilin-mediated modulation of the rat vas deferens SM contractility via the decrease of the expression of L-type VGCCs and increase of the expression of TRPM8.
