pH regulation during ischaemia-reperfusion of isolated rat hearts, and metabolic effects of 2,3-butanedione monoxime

We investigated changes in pH1 during ischaemia-reperfusion of isolated rat hearts using phosphorus nuclear magnetic resonance spectroscopy (31P 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 bicarbonate buffer plus EIPA, pH at the end of 30 min of ischaemia and pH oscillations observed during early reperfusion were lower than in bicarbonate 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+-HCO3− symport. When cardiac contraction was inhibited by 10 mm 2,3-butanedione 2-monoxime (BDM), we observed, in all cases, a less pronounced decrease in pHi at the end of ischaemia, and in pHi oscillations at the onset of reperfusion. These effects were similar to those observed with 150 × 10−8 m verapamil and might thus be related to a decrease in intracellular calcium. However, with BDM, a greater reduction in the pH recovery rate was observed only in HEPES buffer, suggesting a possible phosphatase-like effect affecting the Na+-H+ exchange. Whatever the buffer used, the protective effect of BDM was reflected by an increase in the rate pressure product, which was not observed with verapamil.