Cardiac Na +, K +-ATPase isoenzymes: sensitivity to prednisolone bisguanylhydrazone

Abstract

Prednisolone-3,20-bisguanylhydrazone (PBGH), a steroid derivative, has been shown to inhibit Na +, K +-ATPase isolated from guinea-pig heart or kidney in concentrations significantly lower than those required to inhibit the enzyme obtained from other sources. Because Na +, K +-ATPases obtained from guinea-pig heart or kidney are predominantly of the α isoform, the hypothesis that PBGH selectively inhibits the α isoform over α(+) isoform of the enzyme was tested. Sodium dodecylsulfate polyacrylamide gel electrophoresis of the enzyme preparations revealed the presence of only the higher mobility, α isoform in guinea-pig heart and ferret kidney, whereas those from guinea-pig brain, dog brain and ferret heart showed both high and low mobility isoforms corresponding to α and α(+) isoforms. Na +, K +-ATPase obtained from the guinea-pig heart was most sensitive to PBGH and those isolated from ferret heart or ferret kidney had the lowest sensitivity. Enzyme preparations obtained from dog brain, dog heart or guinea-pig brain had intermediate sensitivity. This spectrum of enzyme sensitivity to PBGH was markedly different from that to ouabain. In ferret heart Na +, K +-ATPase, a low concentration of PBGH preferentially inhibited [ 3H]ouabain binding to the high affinity ouabain binding sites (α(+) isoform). These results indicate that PBGH is not a specific inhibitor of the α isoforms of Na +, K +-ATPase. Affinity of the enzyme for PBGH is determined by the species and tissue rather than isoforms of Na +, K +-ATPase.