Calcium transport by sarcoplasmic reticulum of skeletal muscle is inhibited by antibodies against the 53 KDa glycoprotein of the sarcoplasmic reticulum membrane

ABSTRACT: The effects of an antiserum against the 53-kDa glycoprotein (GP-53) of the Sarcoplasmic reticulum (SR) and of monoclonal antibodies against GP-53 on Ca2+ transport and ATP hydrolysis by SR of rabbit skeletal muscle have been investigated. Preincubation of SR with an antiserum against GP-53 resulted in decreased ATP-driven Ca2+ transport by the SR but had no effect on Ca2+-stimulated ATP hydrolysis. Preincubation of SR with preimmune serum had no significant effect on either Ca2+ transport or Ca2+-ATPase activity. The effect of anti-GP-53 serum was time and concentration dependent. Preincubation of SR with two monoclonal antibodies against GP-53 had no effect on Ca2+ transport or on Ca2+-stimulated ATP hydrolysis. However, preincubation of SR with either monoclonal antibody against GP-53 together with a monoclonal antibody against the Ca2+-ATPase (at levels which had little effect alone) resulted in markedly decreased rates of Ca2+ uptake and ATP hydrolysis. Preincubation of SR with anti-GP-53-serum or with monoclonal antibodies, under the same conditions that inhibited Ca2+ uptake, did not increase the passive permeability of the SR membrane to Ca2+, did not decrease the permeability of the SR to oxalate, and did not cause significant proteolysis of the Ca2+-ATPase. Our results are consistent with the interpretation that GP-53 may modulate the function of the Ca2+-ATPase of the SR membrane. The sarcoplasmic reticulum (SR1) of skeletal and cardiac muscle plays a vital role in controlling the cytosolic concen-tration of Ca2+ (Hasselbach, 1964; Ebashi et al., 1969; Mac-Lennan, 1970). The Ca2+-ATPase is an integral protein of the SR membrane that actively transports Ca2+ from the cytosol to the lumen of the SR (Racker, 1972; Meissner &amp