The effects of calcium channel inhibitors on twitches and noradrenaline contractions of the rat bisected vas deferens.

In the prostatic half of the rat vas deferens, responses to noradrenaline 30 microM were biphasic. Ca-deprivation reduced both phases. The initial part of the noradrenaline contraction was resistant to verapamil (IC50 74.2 microM), methoxyverapamil (IC50 approximately 100 microM) and especially nifedipine (no effect up to 14.4 microM). The late part of this response and the entire response to noradrenaline in the epididymal half were abolished by verapamil (10.2 microM), methoxyverapamil (9.6 microM) or nifedipine (1.44 microM). The first phase of the twitch to single pulse transmural stimulation was abolished by nifedipine (14.4 microM) and inhibited by methoxyverapamil (57.6-96 microM); verapamil was less potent. The second phase of the twitch was totally resistant to nifedipine (14.4 microM), but more sensitive to inhibition by verapamil or methoxyverapamil than was the first. It was concluded that the calcium channel inhibitors can distinguish between three distinct types of calcium ion channel in the rat vas deferens: (1) sensitive calcium channels mediating the noradrenaline response in the epididymal half, and the late part of the noradrenaline response in the prostatic half (2) calcium channels responsible for the first phase of the twitch, blocked by high concentrations of nifedipine (3) calcium channels mediating the second phase of the twitch and the initial response to noradrenaline in the prostatic half, unaffected by nifedipine.