A total ischaemia of one area of the myocardium was produced by ligature of a coronary artery in dogs. After 30 min, 1 hr, 2 hrs, and 4 hrs the ligature was loosened and the artery was for 1--2 hrs reperfused up to 4--7 days. At the end of the ischaemia and after reperfusion the ultrastructure of the myocardium was qualitatively and morphometrically investigated. The findings concerned: loss of glycogen (partly glycogen accumulation), mitochondrial swellings and fusions and development of megamitochondria, loss of cristae, rupture of the mitochondrial outer membranes, relaxation or supercontraction of the myofibrils, vesicular and vacuolar changes of the sarcoplasmic reticulum, oedema of the sarcoplasm, rupture of the sarcolemma. No significant differences of the quantitative parameters could be observed during the ischaemia from 30 min to 4 hrs: myofibrils 53.65--59.74%, mitochondria 26.51--33.59%, sarcoplasm 8.22--11.86%, sarcoplasmic reticulum 1.41--2.63%, lipofuscin 0.05--0.87%, lipids 0.01--0.10%. In comparing the data of the single animals we could determine significant differences between some parameters at the ends of the ischaemic phase and of the reperfusion phase, but as far as the findings are concerned both increases and decreases could be observed. The investigations show that the limit of the reversibility of damages in myocardial cells is about 45 min; in special cases a longer survival time may be taken into account. Reperfusion has different, though not always positive, effects.

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The electron-transparent zone in phagocytized Mycobacterium avium and other mycobacteria: formation, persistence and role in bacterial survival.

After phagocytosis by bone-marrow macrophages, Mycobacterium avium was surrounded by a thick electron-transparent zone (ETZ). The use of various fixation and embedding procedures showed that ETZ did not seem to be an artifactual structure. A quantitative assessment of ETZ frequency was performed at different times after infection of macrophages with SmD and SmT colony variants of M. avium. For SmT-variant-infected macrophages, a higher percentage of ETZ+ bacilli paralleled a higher percentage of intact bacilli than was the case for SmD-infected macrophages. Macrophages were also infected with bacteria killed with UV or gamma rays, H2O2, heat or glutaraldehyde. About 50% of bacilli killed with any of these treatments were found ETZ+ instead of 80-85% with live bacteria. Unlike live bacilli, for which the percentage of ETZ frequency remained stable throughout incubation time, ETZ frequency for killed bacilli decreased with time. ETZ assessment performed on M. tuberculosis H37 Rv for comparison showed that, despite a very low ETZ frequency (8-15%), the percentage of intact bacteria was identical to that observed with M. avium. In contrast, three rapidly growing non-pathogenic species (M. smegmatis, M. phlei and M. fallax) presented a low ETZ frequency after phagocytosis and were rapidly degraded. The process of ETZ formation and its role in bacterial survival are discussed.

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