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

The relationship between maximum shortening velocity (Vmax) and free calcium concentration has been studied in skinned single fibres from rabbit psoas and soleus muscles. At both 10 and 15 degrees C, Vmax 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 in Vmax were observed when the pCa was increased to 6.32. Vmax measured in soleus fibres at 15 degrees 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+ upon Vmax 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.