A component of nerve-evoked contractions of rat vas deferens is blocked by T-type calcium channel antagonists.
In rat vas deferens, nerve mediated-contractions to a single electrical stimulus consist of an early purinergic and a later adrenergic component with differing sensitivities to L-type calcium entry blockers. In the prostatic portion, contractions to a single stimulus are largely purinergic and this response is abolished by L-type calcium entry blockers such as nifedipine. In the epididymal portion, contractions to a single stimulus are largely adrenergic and this response is unaffected by nifedipine. However, Shishido et al. (2009) have shown that a component of contractions to trains of pulses in guinea-pig vas deferens is susceptible to T-type calcium channel blockers. We have investigated the effects of the T-type blockers mibefradil and NNC 55-0396 against contractions in rat vas deferens. Male Wistar rats (250g) were killed by CO2 overdose. Prostatic and epididymal portions of rat vas deferens were stimulated with a single electrical stimulus (supramaximal voltage) every 5 min. In some experiments, responses in epididymal portions were carried out in the presence of nifedipine (10 uM). Both mibefradil and NNC 55-0396 (100 uM) produced inhibition of contractions of epidiymal portions (42.8±5.9% and 63.5±7.5% of control, respectively, n=4 each). However, both agents produced small inhibitions of responses in prostatic portions, presumably by L-type calcium entry block. It is concluded that the T-type calcium channel blockers mibefrabil and NNC 55-0396 block particularly the adrenergic nifedipine resistance response to nerve stimulation in rat vas deferens, and this may suggest that this component of the contraction involves T-type calcium channels.
Shishido T. et al. Neurourol Urodyn. 2009 Feb 19. (Epub ahead of print).