Effects of Bradykinin on Intracellular Calcium Transients in Cardiac Myocytes

Effects of Bradykinin on Intracellular Calcium Transients in Cardiac Myocytes

<P> In spite many evidences has supported the cardioprotective effect of bradykinin, its direct effects at the cell level are still under question. We investigated the both effects of bradykinin (BK) on Ca<SUP>2&#8290;</SUP>-related ionic currents using whole cell voltage clamp technique in rabbit cardiomyocytes and on the intracellular Ca<SUP>2&#8290;</SUP> transient using calcium sensitive fluorescence dye, indo-1AM. Simultaneously with recording intracellular Ca<SUP>2&#8290;</SUP> transients, cell contractility was estimated from the changes in length of the electrical stimulated rat cardiac myocytes. L-type Ca<SUP>2&#8290;</SUP> current decreased by bradykinin at the entire voltage range. Inward tail current increased initially up to its maximum about 4 min after exposing myocytes to BK, and then gradually decreased again by further exposure to BK. This tail current decreased remarkably at washing BK off but slowly recovered ca. 20 min later. The change in cell contractility was similar to that in tail current showing initial increase followed by gradual decrease. Removal of BK brought remarkable decrease in contractility, which was recovered 15∼20 min after cessation of electrical stimulation. Bradykinin increased Ca<SUP>2&#8290;</SUP> transient initially but after some time Ca<SUP>2&#8290;</SUP> transient also decreased coincidentally with contractility. From these results, it is suggested that bradykinin exerts directly its cardioprotective effect on the single myocytes by decreasing the intracellular Ca<SUP>2&#8290;</SUP> level followed by an initial increase in Ca<SUP>2&#8290;</SUP> transient.