PH REGULATION DURING ISCHEMIA-REPERFUSION OF ISOLATED RAT HEARTS, ANDMETABOLIC EFFECTS OF 2,3-BUTANEDIONE MONOXIME

We investigated changes in pH(i) during ischaemia-reperfusion of isola ted rat hearts using phosphorus nuclear magnetic resonance spectroscop y (P-31 NMR). Hearts were separated into three groups according to the perfusion buffer: bicarbonate-buffered Krebs solution, HEPES-buffered Krebs solution, or bicarbonate-buffered Krebs solution plus 10(-6) M 5-(N-ethyl-N-isopropyl) amiloride (EIPA). In HEPES buffer and in bicar bonate buffer plus EIPA, pH at the end of 30 min of ischaemia and pH o scillations observed during early reperfusion were lower than in bicar bonate buffer. Thus, the presence of two pH regulation mechanisms (Na-H+ antiport and Na+-HCO3- symport) was confirmed in the isolated rat heart, while in HEPES buffer, pH was regulated by Na+-H+ antiport, and in bicarbonate buffer plus EIPA, by Na+-HCO(3)( )symport. When cardia c contraction was inhibited by 10 mM 2,3-butanedione 2-monoxime (BDM), we observed, in all cases, a less pronounced decrease in pH(i) at the end of ischaemia, and in pH(i) oscillations at the onset of reperfusi on. These effects were similar to those observed with 150 x 10(-8) M v erapamil and might thus be related to a decrease in intracellular calc ium, However, with BDM, a greater reduction in the pH recovery rate wa s observed only in HEPES buffer, suggesting a possible phosphatase-lik e effect affecting the Na+-H+ exchange. Whatever the buffer used, the protective effect of BDM was reflected by an increase in the rate pres sure product, which was not observed with verapamil. (C) 1995 Academic Press Limited