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

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Abstract
The effects of khellin on contractile responses and 45Ca2+ flux have been studied in rat isolated aortae. Khellin (10−5- 3.2 times 10−4M) produced a concentration-dependent inhibition of noradrenaline (10−6 M) and high K+ (80 mM)-induced contractions. At 3.2 times 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.