The effect of calcium on the maximum velocity of shortening in skinned skeletal muscle fibres of the rabbit

Summary The relationship between maximum shortening velocity (V_max) and free calcium concentration has been studied in skinned single fibres from rabbit psoas and soleus muscles. At both 10 and 15° C,V_max measured in the psoas fibres was found to decrease by 40% when the pCa (-log[Ca²⁺]) was increased from 5.49 (maximally activating) to 6.21. Further decreases inV_max were observed when the pCa was increased to 6.32.V_max measured in soleus fibres at 15° C also decreased when the Ca²⁺ concentration was lowered, though the magnitude of this effect was slightly less than in the psoas fibres. Thus, a distinct effect of Ca²⁺ uponV_max has been shown to occur in mammalian skeletal muscle. The occurrence of this effect in both fast and slow muscle types may indicate that the underlying mechanism in the two cases is similar.