Monoclonal antibodies to dog heart sarcoplasmic reticulum. Application of the mAbs for studies of the structure and function of Ca2+-pumps.

One of monoclonal antibodies (mAbs) raised against purified dog heart sarcoplasmic reticulum (SR) efficiently decreases Ca2+-pump and Ca2+-ATPase activities of various SR preparations. The ATPase activity that is insensitive to the mAb (10-20% of the initial value) is present both in light and heavy fractions of rabbit skeletal muscle SR. The residual activity is completely blocked by 2 microM vanadate. The inhibition of the ATPase by the mAb is prevented in the presence of a nonionic detergent C12E8. It is concluded that the inhibiting effect of the mAb takes place when the Ca2+-ATPase exists in an oligomeric form. Another mAb does not affect SR functions and is specific only for Ca2+-ATPase from cardiac and slow muscle cells. Decrease in the Ca2+-pump activity of SR fractions from ischemic myocardium is accompanied by a diminished binding of both mAbs with the antigen. The mAbs described could be employed for differentiating endoplasmic reticulum and plasma-lemmal calcium pump systems, visualization of SR in the cells and estimating its amount in membrane preparations and tissue homogenates.