Fig. 4. Ca²⁺ currents at different voltages and the effect of nifedipine. (A) Whole-cell membrane currents in response to the step depolarisations (same pulse protocol as in Fig. 3A except that the pulse duration was increased to 25 ms). Eleven traces are superimposed. The bath solution was 4Ca-ASW containing 4 µmol l^–1 TTX, and the pipette solution was Cs-asp. Cell membrane capacitance (C_m)=109.0 pF. (B) Current–voltage (I–V) relationship of the peak currents obtained from eight experiments. Values are means ± S.D. (C) Superposition of five current records at +10 mV pulses before (1, 2) and after (3–5) application of 10 µmol l^–1 nifedipine. Records 1 and 2 were obtained 3 and 6 min after the whole-cell configuration was made, and records 3, 4 and 5 were obtained 2, 4 and 6.5 min after the nifedipine application. Nifedipine was applied after record 2 was taken. C_m=138.2 pF.