A component of nerve-evoked contractions of rat vas deferens is blocked by T-type calcium channel antagonists.

Sai Wang Seto, James R. Docherty. Department of Physiology, Royal College of Surgeons in Ireland, 123 St. Stephen’s Green, Dublin 2, Ireland.

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).