[Elucidation of reversibility in myocardial injury during hypoxia and reoxygenation in papillary muscles of rats].

ABSTRACT

We reported the calcium release of sarcoplasmic reticulum (SR) is the major source of activator calcium to postrest contraction (PRC), and that the transsarcolemmal calcium influx is (the major source of activator calcium) to regular contraction in rats. In this study we investigated the combined effects of hypoxia and glucose elimination on PRC and regular contraction. In other words, using papillary muscles of rats, to elucidate the characteristics of reversible or irreversible myocardial injury after ischemia, we investigated the effects of hypoxia on both SR and sarcolemmal functions. After 90 min hypoxia (the first hypoxia-90 min), regular contraction was significantly more reduced than PRC (p less than 0.001; n = 16). With 90 min of reoxygenation, the recovery from hypoxic injury of PRC was better than recovery from injury of regular contraction (p less than 0.01; n = 16). After either 30 min hypoxia (the second hypoxia-30 min) or 60 min hypoxia (the second hypoxia-60 min), regular contraction was also more reduced than PRC, respectively (p less than 0.001; n = 8). However, the recovery from both the second hypoxic injury-30 min and the second hypoxic injury-60 min of PRC was not significantly different from that of regular contraction, respectively (NS; n = 8). Percentages of diastolic tension, which were normalized by baseline regular contraction, increased during hypoxia and decreased incompletely after reoxygenation. After the first reoxygenation of 90 min, 1 microM noradrenaline significantly augmented the magnitude of regular contraction (p less than 0.05; n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)