Do calcium antagonists act directly on calcium channels to alter baroreceptor function?

This study examined the effects of antagonists known to act on voltage-dependent calcium channels (chiefly nitrendipine, diltiazem and verapamil) on arterial baroreceptor function. Single fiber discharge of aortic arch baroreceptor preparations of the rat was not altered at concentrations ranging from 10^-11 to 10^-6 M. Increasing pressure in an isolated perfused carotid sinus in the cat produced a reflex arterial pressure response which was not altered significantly when the carotid perfusate contained an antagonist concentration of 10^-7 to 10^-6 M. A higher concentration (10^-5 M) of all three antagonists decreased baroreceptor discharge and depressed the reflex response. In addition, nimodipine and nifedipine had uniformly similar dose-related effects. It is likely that the effects found at the elevated concentrations are nonspecific and probably are independent of voltage-dependent calcium channels. No differences between the dihydropyridine blockers and verapamil were found even at very high doses. Our results suggest that within the range of doses used clinically these antagonists do not directly affect baroreceptor function. In addition, the present results reinforce the notion that voltage-dependent calcium channels are not importantly involved in baroreceptor transduction as suggested by earlier studies of the effects of changing external calcium concentration.