Fig. 6. (A) Example of a recording of the calcium inward current after treatment with 40 mmol l^–1 tetraethyl ammonium chloride, 10^–6 mol l^–1 TTX and 40 mmol l^–1 4-aminopyridine treatment. (B) Effect of the addition of 10^–5 mol l^–1 of serotonin (5HT) on the calcium current. (C) Blockade of the calcium current after addition of cobalt ions in the medium bathing the cells and in the pipette. (D) Imposed voltages. Vertical bars, 0.1 nA (A–C) and 60 mV (D); horizontal bar, 10 ms.