Radioligand binding to muscle homogenates to quantify receptor and ion channel numbers

Quantitation of the number of receptor or ion channel proteins in muscle that may be changed as a result of disease, development, or experimental manipulation can be achieved by radioligand binding assays. The problem of apparent specific binding to filters, which severely distorts these assays, is described. Results show that when techniques are applied to minimize both high nonspecific binding and spurious specific binding to filters, equilibrium and nonequilibrium binding assays can be effectively used to measure binding site densities in muscle homogenates. As no sites are lost during homogenate preparation, changes in binding site density that are not apparent when normalized per mg protein are revealed by normalizing the number of sites either per muscle or by muscle fiber diameter. Thus, the resolution of problems inherent in homogenate binding allows the use of these preparations to compare the plasticity and control of ion channels and receptors under a wide variety of experimental conditions.