After long (1.2 s) saturating pulses to +40 mV the biphasic deactivation was measured at tail potentials, Vt, ranging from -80 to -60 mV. Example traces (A: no [Na+]i; B: 65 mm[Na+]i) are at Vt= -70 mV. The time course was fitted by a bi-exponential function (eqn (1)) and mean values of the resulting time constants (C) (squares, slow time constants; circles, fast time constant) and of the ratio of the coefficients of the fast and the slow component, af/as (D) are plotted as a function of Vt. No [Na+]i, ○; 65 mm[Na+]i, •.