Ultrastructural and contractile characteristics of isolated papillary muscle exposed to acute hypoxia

Abstract

The ultrastructure of left posterior papillary muscles isolated from adult guinea pigs was examined before and after 30 min of hypoxia. A rapid decline in developed tension was observed during early hypoxia but at the time of fixation the activity had stabilized at 29% of the prehypoxia value. Control muscles bathed only in oxygenated Tyrode's solution resembled intact muscle fixed <i>in situ</i>, except for the presence of more intramitochondrial granules. Hypoxic muscles showed no signs of severe damage. Myofibrils were normal except for widened Z bands. Mitochondria were very often swollen and seldom contained intramitochondrial granules. Since the disappearance of intramitochondrial granules was also observed in hypoxia, additional cytochemical studies were performed to determine the content of the intramitochondrial granules. Unstained sections of post-osmicated control and hypoxic muscle containing intramitochondrial granules were examined. The granules before and after the hypoxic period had an average diameter of 330 . Electron dense granules were not removed by decalcifying agents, 2% formic acid or 2 mm EDTA without prior oxidation by 5% periodic acid or 2% hydrogen peroxide. Inorganic material in granules was not seen after microincineration at 500°C. The intramitochondrial granules do not change in size, yet they increase in number after prolonged incubation in 95% oxygen and decrease in number in 95% nitrogen. The number of granules may be related to the availability of substrate for the organic matrix of the granules.