Calcium Binding by Skeletal Muscle Sarcolemma

Abstract

Abstract Plasma membranes isolated from rabbit muscle possessed the ability to bind and accumulate calcium ions; these processes required ATP and Mg2+. Binding of Ca2+ was rapid, reaching a maximum within 30 s and was greatly increased in the presence of oxalate or phosphate. The concentrations of Ca2+, Mg2+, and ATP required for half-maximal ATP-dependent calcium binding were 20 µm, 150 µm, and 20 to 30 µm, respectively. In the presence of oxalate, half-maximal calcium accumulation occurred at 120 µm ATP and 500 µm Mg2+. Both binding and accumulation were highly sensitive to pH, the maximum being at pH 5.5 to 6.0. Bound calcium could be released by depleting ATP from the medium. Sodium or potassium (100 mm) and high concentrations of Mg2+ promoted, while La3+ up to 6 mm inhibited the release process. Rapidity of the binding and release of Ca2+ by the sarcolemma suggests its possible involvement in the excitation-contraction coupling mechanism in muscle.