Inhibition of Inositol(1,4,5)Trisphosphate Generation by Endothelin-1 During Postischemic Reperfusion

Abstract

Background —Reperfusion of ischemic rat hearts in the presence of thrombin or norepinephrine but not endothelin-1 causes the generation of inositol 1,4,5-trisphosphate (Ins 1,4,5P 3 ) and arrhythmias. The present study investigates the effect of endothelin-1 on these responses. Methods and Results —Ins 1,4,5P 3 generation was quantified by use of [ 3 H] labeling and high-performance liquid chromatography as well as by mass analysis. Twenty minutes of global ischemia followed by 2 minutes of reperfusion increased [ 3 H]Ins 1,4,5P 3 from 2828±265 to 5033±650 cpm/g tissue in the presence of thrombin 2.5 IU/mL and to 4561±286 cpm/g tissue in response to release of norepinephrine (n=4, P <0.01) in both cases. Reperfusion in the presence of endothelin-1 alone caused no change in Ins 1,4,5P 3 (2762±240 cpm/g tissue), but when added together with thrombin or norepinephrine, endothelin-1 reduced the Ins 1,4,5P 3 responses to 2313±197 and 1764±168 cpm/g tissue, respectively (n=4, P <0.01 in both cases). Similar inhibitory interactions between endothelin-1 10 nmol/L and thrombin 2.5 IU/mL were observed under normoxic conditions in nonperfused ventricle, eliminating the possibility that excessive vasoconstriction was responsible. In parallel studies, endothelin-1 suppressed the development of reperfusion arrhythmias initiated by either thrombin (ventricular fibrillation, 75% to 39%, n=16 to 18) or norepinephrine (83% to 8%, n=12 to 22) ( P <0.01 in both cases). Conclusions —Inhibition of Ins 1,4,5P 3 generation during myocardial reperfusion by endothelin-1 represents a novel antiarrhythmic mechanism.