THE EFFECTS OF HYPOXIC STRESS ON THE FINE-STRUCTURE OF THE FLOUNDER HEART (PLATICHTHYS-FLESUS)

1. Flounder hearts were examined by conventional transmission electron microscopy. Hearts showed clear evidence of a coronary circulation but no intrinsic conduction network or innervation was detected. 2. The box-like cells showed many surface inpocketings and many scattered glycogen granules and membrane bound liposomes. The nucleus position was variable and the cells contained numerous small ovoid mitochondria. 3. Dark staining intercalated discs with clear nexal and desmosomal areas separated individual cells. 4. No organized T-tubular system or sarcoplasmic reticulum was present but the cells displayed abundant surface vesicles which may perform the physiological role of the latter. 5. Hearts of flounder subjected to 3 weeks hypoxia showed striking changes to the mitochondria which were smaller than in controls and there was evidence of increased mitochondrial budding and also evidence of mitochondrial necrosis. 6. Hypoxically-stressed hearts exhibited normal liposome populations but increased glycogen granule deposits. These hearts also showed evidence of myofibril degeneration with torn Z discs and with a build up of fibrous material. 7. It is concluded that the cellular damage seen in hypoxic cells may be due to excessive calcium accumulation or increased catecholamine release.