Cytotoxic effect of phenazine methosulphate on the isolated frog heart

1. Perfusion of isolated frog hearts with phenazine methosulphate (PMS) at 0.3-1.0 mM caused a fall in amplitude and frequency of beat, and finally a cessation of contractile activity, together with widespread ultrastructural damage. 2. Sarcolemma blebs were a characteristic feature of the damage. 3. No protection was provided by mannitol (10-100 mM), superoxide dismutase, catalase or a pHo of 6.6. 4. Potassium ferricyanide (1-6 mM), an artificial electron acceptor, also caused ultrastructural damage. 5. Comparisons are made with the oxygen paradox of mammalian heart, and the possible role of Ca2+ fluxes and oxygen radicals in muscle damage are discussed.