Calcium binding and the activation of fibrillar insect flight muscle

A new method has been used to measure calcium binding in intact glycerol extracted muscle fibres; results with rabbit psoas muscle are in agreement with previous work. Lethocerus cordofanus flight muscle bound up to 140 μM calcium at high affinity in the presence of ATP; removal of the ATP increased the maximum amount bound to 210 μM and the affinity approx. 3-fold. Calcium binding in the presence of ATP correlated with calcium activation of the ATPase but no changes in calcium binding occurred when the muscle was further activated by stretching.