Voltage-gated Ca2+ channel in mouse myeloma cells.

Electrical properties of the cell membrane were studied in the neoplastic lymphocyte, mouse myeloma cell line S194, by using the whole-cell patch clamp technique. Inward Ca2+ currents due to voltage-gated Ca2+ channels were found. The current, which decayed exponentially after reaching a peak, was first activated at about -50 mV and attained its maximum peak amplitude at about -20 mV in a 10 mM Ca2+ solution. Outward current was negligible for the potential range more negative than +30 mV. The channel was permeable to Sr2+ and Ba2+ in addition to Ca2+. Among these species, Sr2+ carried the greatest current. The time constants of the decay of the current depended neither on the species nor on the concentration of charge carrier. The steady-state inactivation was observed at potentials more negative than those at which the inward Ca2+ current was activated. Thus, we concluded that the inactivation of the channel was mainly voltage dependent. For reasons that are not yet understood, the amplitude of the Ca2+ current varied greatly among cells.