Abstract

The nonfusing muscle cell line BC3H1 expresses functional Na and Ca channels similar to those found in skeletal muscle (1). We have utilized a monoclonal antibody that cross-reacts with a 45-50-kDa glycoprotein in differentiated BC3H1 myocytes but not in cardiac or neuronal cells. This antibody, MAb1223, specifically modulates 45Ca influx and slowly activating, dihydropyridine-sensitive Ca currents when added to BC3H1 myocytes. Low-threshold, dihydropyridine-insensitive Ca currents and Na and K currents are unaffected. MAb1223 action is voltage dependent. At very negative holding potentials, similar to those of the resting cell, MAb1223 increases slow Ca current without significant changes in the voltage dependence of activation. At more positive potentials, at which channel opening probability is reduced by inactivation, exposure to MAb1223 reduces current. Agonist and antagonist dihydropyridines modulate the action of MAb1223 on the slow Ca channel in a manner that suggests that their respective binding sites may interact directly with the channel.