Effects of intracellular calcium injection on steady state membrane currents in isolated single ventricular cells

The effect of intracellular calcium injection on steady state membrane currents was studied in isolated guinea-pig ventricular cells with a single-electrode voltage clamp method. When the membrane potential was clamped at the resting potential, an intracellular injection of Ca induced an inward current. The steady state current-voltage (I-V) curves before and after Ca injection crossed at around -22 mV. Above this potential, Ca increased the current in the outward direction. A linear relationship was observed between the current mediated by the increase of intracellular Ca and membrane potentials from -60 to +10 mV. This current component may correspond to the Ca-activated non-selective cation channels recorded by the patch clamp technique (Colquhoun et al., 1981).