Ionic radius selectivity of skeletal muscle membranes

Abstract

THERE have been several reports^1–3 that the trivalent lanthanide cations bind to sites on membranes that are normally occupied by Ca²⁺. In skeletal muscle, Ca²⁺ is important for the functions of both the outer sarcolemma⁴ and the internal sarcoplasmic reticulum^5,6. Here I report the inhibitory effects of 13 lanthanide ions on these Ca²⁺-mediated functions. The relationship between ionic radius and the degree of inhibition is different in these two membranes. There are features of the data which are difficult to explain by assuming that charge density alone determines cation recognition at the membrane surface. But it would also be too simplistic to suggest that the lanthanide ions are selected only on the basis of ionic radius.