CALCIUM-CHANNEL CURRENT IN CULTURED RAT MESANGIAL CELLS

The presence of voltage-dependent calcium channels has been suggested in mesangial cells by using calcium-sensitive fluorescent probes. However, direct electrophysiological evidence for voltage-dependent calcium channels has not yet been presented. In this study voltage-dependent calcium channels were studied in cultured rat mesangial cells. Whole-cell patch-clamp experiments were done with 50 mM Ba2+ as a charge carrier. Step depolarizing pulses from a holding potential of -50 mV produced an inward barium current at potentials more positive than -10 mV, and a peak current (10-45 pA) was obtained at a membrane potential of approximately +30 mV. The inward current was augmented by 1 00 nm Bay K 8644, attenuated by 1 muM nifedipine, and abolished by 50 muM Cd2+. These results indicate that the inward current is a barium current flowing through L-type calcium channels. This may be the first study that demonstrates the presence of L-type calcium channels in mesangial cells.