Deterioration induced by physiological concentration of calcium ions in skinned muscle fibres

The deteriorating effect of microM order of Ca2+ on skinned frog skeletal muscle fibres was studied from the view point of the digestion of proteins by calcium-activated neutral protease (CANP). Tension developed in solutions containing no MgATP (rigor solution) decreased irreversibly with the addition of Ca2+ in quantities of more than 0.1 microM. Low temperature was seen to suppress (Q10 greater than 4), and neutral pH to maximize, this decrease in tension. In rigor solution containing Ca2+, SDS electrophoresis indicated that a 95 k dalton component (alpha-actinin) was released from the fibre; electron micrography showed the disappearance of Z-lines. These results suggest that one of the causes for decrease in rigor tension is the proteolytic activity of CANP, and its inhibitors were shown to be quite useful in experiments on skinned fibre.