The properties of sarcoplasmic vesicles from rats with 20,25-diazacholesterol induced myotonia

The calcium transport system of sarcoplasmic vesicles isolated from rats which have been treated with 20,25-diazacholesterol to induce myotonia differs in two respects from that of normal vesicles: 1 The calcium storing capacity and the initial rate of calcium uptake are increased provided that the calcium level in the system is high. 2 The calcium concentrating ability of the vesicles from myotonic animals is less than that of normal animals. In accordance with this change the vesicles from myotonic animals suppress the myofibrillar ATPase less effectively. The reduction of concentrating ability is found to be connected with a significant increase of the calcium permeability of the membranes in the presence as well as in the absence of ATP.