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.