Potassium and calcium currents and action potentials in mouse Balb/c 3T3 fibroblasts

The electrical properties of Balb/c 3T3 mouse fibroblasts were studied with the whole-cell patch clamp technique. In current clamp mode a resting potential of -75.5 +/- 2.1 mV was recorded. In voltage clamp mode an inward current was also observed at potentials negative to Vm. This current crossed the 0-current axis at a voltage near Vm, and rectified at more positive potentials; the degree of rectification was dependent on [K+]o. At potentials positive to -30 mV a transient inward current was observed, showing a peak amplitude of -193 +/- 36 pA at +10 mV; the current amplitude was dependent on voltage and [Ca2+]o, it was strongly increased by 20 mM BaCl2 and abolished by 2 microM verapamil and 1 microM nifedipine. These cells, in response to depolarizing stimuli, develop slow action potentials, probably supported by the Ca2+ current.