Comparative effects of T-type and L-type Ca(2+)-antagonists against noradrenaline-induced contractions of human vas...

To investigate the effects of the relatively selective T-type Ca(2+)-antagonists, mibefradil and flunarizine, and the L-type Ca(2+)-antagonist, nifedipine, on the contractions of longitudinal and circular muscles of human vas deferens, to elucidate the possible involvement of T-type voltage-gated Ca(2+) channels (VOCs) in the contractile function of the tissue.

Human vas deferens specimens from elective vasectomies were cut into strips of longitudinal muscle or transversely into rings of circular muscle. These were set up for tension recording and superfused with Krebs' medium (36 degrees C). Contractions were evoked by noradrenaline or high [K(+)](o) (in the presence of the L-type Ca(2+) agonist, FPL 64176) and the effects of Ca(2+) antagonists were determined.

Noradrenaline (0.1-100 micromol/L) evoked rhythmic and tonic contractions of longitudinal and circular muscles, which were potently inhibited by nifedipine (

These results indicate that noradrenaline-induced contractions of human vas deferens depend primarily on nifedipine-sensitive L-type VOCs, as opposed to mibefradil/flunarizine-sensitive T-type VOCs. The effects of mibefradil and flunarizine, at concentrations found to be effective against noradrenaline-induced contractions, involve the blockade of L-type VOCs. The modest differential effect of mibefradil in longitudinal and circular muscle is discussed in relation to factors that modulate activation and drug-sensitivity of L-type VOCs.