Brief Communications Effects of Proton Buffering and of Amiloride Derivatives on Reperfusion Arrhythmias in Isolated Rat Hearts

We investigated the hypothesis that an accelerated Na+O-HWi exchange on reperfusion may lead to a displacement of the 3 [Nat] [Ca2'] i/o equilibrium in favor of an arrhythmogenic rise in cytosolic [Ca2+]. Supporting evidence was obtained by subjection of isolated rat hearts to 15 minutes of low-flow (5% of control) ischemia and 2 minutes of reperfusion in the presence of a Krebs-Henseleit HEPES buffer (pH 7.4) containing lactate (10 mM). At first, the [HEPES] was fixed at 5 mM; then, 2 minutes before reflow, either the [HEPES] was varied from 50 to 1 mM to slow HWO washout, or increasing concentrations of 5-(N,N-dimethyl)-amiloride (Ki 7 ,uM) or 5-(N,N-hexamethylene)-amiloride (Ki 0.2 ,M) were added for inhibition of Na+-H+ exchange. In each case, reperfusion ventricular arrhythmias were reduced by 69-73% (p <0.001). (Circulation Research 1990;66:1156-1159)