Cromakalim blocks the purinergic response evoked in rat vas deferens by single-pulse electrical stimulation

The present study was carried out to look at the influence of the K+ channel opener cromakalim, compared with suramin and prazosin, on the contractile response evoked by single-pulse field stimulation and exogenous agonists in epididymal and prostatic portions of rat vas deferens. In the epididymal portion suramin abolished the first phase of the response to single shock, prazosin deeply affected the second phase and a combination of both antagonists almost completely abolished both phases. Cromakalim was able to inhibit in a concentration-dependent manner the first purinergic phase (pD2 = 5.90 +/- 0.11), leaving practically unaffected the second, adrenergic phase. This inhibitory effect of cromakalim on the electrically evoked response was counteracted by glibenclamide. Cromakalim and prazosin, but not suramin, affected the response to exogenous noradrenaline. Suramin but not cromakalim was able to antagonize responses to alpha, beta-methylene-ATP. In the prostatic portion because of a less clear discrimination between adrenergic and purinergic phases of the electrically evoked response, the picture was less clear although the trend was identical. Cromakalim was not able to antagonize the response to ATP. It is concluded that in rat vas deferens cromakalim inhibits purinergic transmission by acting prejunctionally.