Effects of khellin on contractile responses and 45Ca2+ movements in rat isolated aorta

The effects of khellin on contractile responses and 45Ca2+ flux have been studied in rat isolated aortae. Khellin (10(-5)-3.2 x 10(-4) M) produced a concentration-dependent inhibition of noradrenaline (10(-6) M) and high K+ (80 mM)-induced contractions. At 3.2 x 10(-4) M, khellin increased cAMP levels and reduced 45Ca2+ influx in resting tissues and in tissues stimulated by noradrenaline (10(-5) M) and high K+ without affecting basal 45Ca2+ efflux or noradrenaline induced 45Ca2+ efflux. It is concluded that in rat isolated aorta, khellin caused a non-specific inhibition of Ca2+ influx but may also exhibit intracellular actions, thus decreasing the availability of Ca2+ required for activation. One or more of these mechanisms may be related to an increase in intracellular cAMP levels.