Species-dependent changes in mechano-energetics of isolated cardiac muscleduring hypoxia

The present study investigates the mechanical and energetic changes induced by hypoxia in isolated cardiac muscles of different species characterized by different myosin isoforms. Classic mechanical parameters of contraction and energetic parameters derived from the tension-velocity relationship wer e studied in rat and guinea pig left ventricular papillary muscles and in f rog ventricular strips before and after 15 min hypoxia (n = 8 in each group ). The isomyosin pattern is predominantly V1 with high ATPase activity in r at and V3 with low ATPase activity in guinea pig and frog heart ventricles. At baseline, cardiac mechanical performance was greater in rat than in gui nea pig and frog muscle, but the economy of tension generation did not diff er significantly between the three species. Hypoxia significantly decreased myocardial mechanical performance in all three groups. Mechanical impairme nt was more marked in rat than in the other two species and was intermediat e in guinea pig. The energetic consequences of hypoxia differed according t o species and in a different manner from the mechanical parameters. Hypoxia decreased the economy of tension generation in rat heart, in contrast to n o change in guinea pig and frog muscle. These results suggest that in terms of mechano-energetic properties, cardiac muscles with V1 isomyosin were mo re sensitive to hypoxia than those containing V3 isomyosin.