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-triphosphate [Ins(1,4,5)P3] and arrhythmogenesis via norepinephrine stimulation of alpha1-adrenergic receptors. The present study examines arrhythmogenic effects of thrombin-stimulated Ins(1,4,5)P3 release under these conditions.


RESULTS
[3H]Ins(1,4,5)P3 release was measured in [3H]inositol-labeled rat hearts by high-performance liquid chromatography. Arrhythmia studies were performed in buffer-perfused rat hearts. Two-minute reperfusion after 20 minutes of global ischemia increased [3H]Ins(1,4,5)P3 from 1123 +/- 77 to 2238 +/- 44 cpm/mg tissue. No increase was observed in catecholamine-depleted hearts (755 +/- 89 cpm/mg). The addition of thrombin (5 IU/mL) or thrombin receptor agonist peptide (TRAP(1-6), 50 micromol/L) restored the reperfusion Ins(1,4,5)P3 response (thrombin, 1518 +/- 68 cpm/mg and TRAP(1-6), 1755 +/- 128 cpm/mg). Ins(1,4,5)P3 release initiated by norepinephrine or thrombin was inhibited by gentamicin (150 micromol/L; 986 +/- 52 and 868 +/- 125 cpm/mg, respectively). The thrombin response was inhibited by the phospholipase C inhibitor U-73122 (5 micromol/L; 394 +/- 59 cpm/mg) but not by its inactive isomer U-73343. The norepinephrine response was not inhibited by U-73122 (2126 +/- 74 cpm/mg). Ventricular tachycardia and ventricular fibrillation were observed in intact hearts but not in hearts from catecholamine-depleted rats (ventricular fibrillation duration, 110 +/- 19 versus 0 +/- 0 seconds). The addition of thrombin or TRAP(1-6) increased arrhythmias in catecholamine-depleted hearts (112 +/- 32 and 89 +/- 28 seconds, respectively). Gentamicin and U-73122 but not U-73343 prevented thrombin-induced arrhythmias. Gentamicin inhibited norepinephrine-initiated arrhythmias, but U-73122 was ineffective.


CONCLUSIONS
This study demonstrates that the development of reperfusion arrhythmias under these conditions depends on the release of Ins(1,4,5)P3.
Jacobsen
A N
AN
Cellular Biochemistry Laboratory, Baker Medical Research Institute, Melbourne, Australia.
Du
X J
XJ
Lambert
K A
KA
Dart
A M
AM
Woodcock
E A
EA
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced* / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008297:Male; D015428:Myocardial Reperfusion Injury / Q000378:metabolism* / Q000503:physiopathology; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013917:Thrombin
D015544:Inositol 1,4,5-Trisphosphate; D013917:Thrombin; D009638:Norepinephrine