Fig. 4 The reversal potential of the hyperpolarisation-induced current depends on the external Cl^– concentration. Current–voltage relationships of tail currents as shown in Fig. 3A, right-hand side. Averages of paired measurements in three fibres, performed first with [Cl^–]_o=65 mmol l^–1 and then with [Cl^–]_o=20 mmol l^–1. The reduction of [Cl^–]_o led to a positive shift of the reversal potential, i.e. from –18.2±3.8 mV to +2.2±1.8 mV. K⁺ currents were blocked by means of 20 mmol l^–1 TEA, 1 mmol l^–1 4-aminopyridine (4AP) and 0.1 mmol l^–1 quinidine.