CHANGES IN THE ULTRASTRUCTURE OF RAT MYOCARDIUM INDUCED BY HYPOKALAEMIA

Changes in the ultrastructure of adult rat ventricular muscle induced by in vitro perfusion with hypokalaemic Krebs‐Ringer solutions are described. In all experiments the [Ca 2+ ] was 1·27 mM./l. After perfusion with [K + ]=0, the myofibrils show severe contractures; after [K + ]=1·19 or 2·5 mM./l. perfusion, disintegration of the thin filaments was shown; disappearance of myofibrillar insertion plaques at the intercalated discs was observed after perfusion with [K + ] ≤ 1·19; with 〉 2·5 mM./l [K + ], normal ultrastructure was retained.