ARRHYTHMOGENIC ACTION OF THROMBIN DURING MYOCARDIAL REPERFUSION VIA RELEASE OF INOSITOL 1,4,5-TRIPHOSPHATE

Background Cardiac reperfusion initiates release of inositol 1,4,5-tri phosphate [Ins(1,4,5)P-3] and arrhythmogenesis via norepinephrine stim ulation of alpha(1)-adrenergic receptors. The present study examines a rrhythmogenic effects of thrombin-stimu lated Ins(1,3,5)P-3 release un der these conditions. Methods and Results [H-3]Ins(1,4,5)P-3 release w as measured in [H-3]inositol-labeled rat hearts by high-performance li quid chromatography. Arrhythmia studies were performed in buffer-perfu sed rat hearts. Two-minute reperfusion after 20 minutes of global isch emia increased [H-3]Ins(1,4,5)P-3 from 1123+/-77 to 2238+/-44 cpm/mg t issue. No increase was observed in catecholamine-depleted hearts (755/-59 cpm/mg). The addition of thrombin (5 IU/mL) or thrombin receptor agonist peptide (TRAP(1.6), 50 mu mol/L) restored the reperfusion Ins( 1,4,5)P-3 response (thrombin, 1518+/-68 cpm/mg and TRAP(1.6), 1755+/-1 28 cpm/mg). Ins(1,4,5)P; release initiated by norepinephrine or thromb in was inhibited by gentamicin (150 mu mol/L; 986+/-52 and 868+/-125 c pm/mg, respectively). The thrombin response was inhibited by the phosp holipase C inhibitor U-73122 (5 mu mol/L; 394+/-59 cpm/mg) but not by its inactive isomer U-73343. The norepinephrine response was not inhib ited by U-73122 (2126+/-74 cpm/mg). Ventricular tachycardia and ventri cular fibrillation were observed in intact hearts but not in hearts fr om catecholamine-depleted rats (ventricular fibrillation duration, 110 +/-19 versus 0+/-0 seconds). The addition of thrombin or TRAP(1.6) inc reased arrhythmias in catecholamine-depleted hearts (112+/-32 and 89+/ -28 seconds, respectively). Gentamicin and U-73122 but not U-73343 pre vented thrombin-induced arrhythmias. Gentamicin inhibited norepinephri ne-initiated arrhythmias, but U-73122 was ineffective. Conclusions Thi s study demonstrates that the development of reperfusion arrhythmias u nder these conditions depends on the release of Ins(1,4,5)P-3.