Sodium-free contractures in frog myocardium damaged by catecholamines

Abstract 1. 1. Sodium-free contractures were studied in myocardial strips from R. pipiens with extracellular sodium (Na o + ) replaced by choline chloride and extracellular calcium (Ca o 2+ ) varied with EGTA-buffer. Normal myocardium was compared with that damaged by adrenaline (ADR) or isoproterenol (ISO). 2. 2. Frog myocardium, damaged by in vivo injections of catecholamines, remained relaxed when exposed to Na + Ca 2+ -free solutions. Only in 2 out of 18 experiments were small contractures observed after several hours. 3. 3. Addition of KCN to the Na + Ca 2+ -free solution caused small contractures after several hours in 7 out of 10 experiments. 4. 4. The time to maximum Na + free contractures was correlated to Ca o 2+ in a dose-dependent manner, but not influenced by catecholamine-induced myocardial damage. 5. 5. Cell injury in the frog heart after in vivo injections of catecholamines does not affect the sarcolemmal Na + Ca 2+ -exchange and is not associated with passive leakage of Ca 2+ from the extracellular to the intracellular space.