Differential inhibitory effect of taurine on contractile responses to potassium and noradrenaline in rabbit ear artery

In the rabbit ear artery, taurine reduces in a reversible and dose-dependent manner the increase in vascular tone induced by a depolarizing medium (54 x lo3 p~ KCI). On the other hand, the contraction induced by a supramaximal dose of noradrenaline (5 p ~ ) is hardly affected by taurine (Franconi et al 1982). To establish that this apparently specific antagonism of contraction was not limited to the test dose of the stimulatory agent used, cumulative dose-response curves to noradrenaline and KCI were determined in the presence or absence of 40 X 1 8 PM taurine. The vasodilator action of taurine could be ascribed to an interaction with calcium handling (Franconi e t a1 1982). An interaction between calcium and taurine has been described in many tissues (Dolara et all973; Chovan et a1 1980; Azari & Huxtable 1980). Furthermore, recent findings show that the inotropic effect of taurine in cardiac tissue (Bandinelli et al 1981; Khatter et al 1981) and 45Ca2+ uptake in retina (Lopez-Colomb & Pasantes-Morales 1981) is strictly dependent on extracellular calcium concentrations. In view of these reports we have examined the influence of different calcium concentrations on the vasodilator action of taurine on KCI-induced contractions in the rabbit ear artery.