[Effects of Na(+)-HCO3- symport on ischemia/reperfusion injury; Na+/H+ exchanger inhibitor and buffer composition].

We studied the impact of perfusate buffer composition on the relative degree of protection afforded by Na+/H+ exchanger (NHE) inhibition during ischemia as opposed to during reperfusion. Isolated rat hearts were perfused with bicarbonate- or HEPES-buffered medium. There was infusion of HOE 694 immediately before ischemia, during initial reperfusion, or during both of these periods. With bicarbonate-buffered medium, HOE 694 improved the post-ischemic recovery of left ventricular developed pressure (LVDP) when given before ischemia and before ischemia plus during reperfusion. In the presence of HEPES-buffered medium, however, HOE 694 significantly improved recovery of LVDP in all protocols. HOE 694 also provided an almost complete recovery of LVDP (88 +/- 9% vs 30 +/- 7% in controls) when given before ischemia plus during reperfusion. In conclusion, our results suggest that the influence of NHE activity during reperfusion on the extent of functional recovery is modulated significantly by perfusate buffer composition.