Figure 6. Dependence of time constant for receptor current recovery on external [Na⁺].

A, mean time constants for single exponential curves fitted to receptor current recovery in solutions with modified Na⁺ concentration following IBMX exposures of 1 s (▴, as in Fig. 4) or 2 s (▿) duration. Data have been normalized for each cell to the time constant measured in normal Ringer (111 mm[Na⁺]). Data points represent the means of 3–18 cells; error bars denote standard errors of the mean. B, rate constants, calculated as the reciprocal of the mean time constants for the 1 s IBMX exposures in A, normalized to the rate constant in normal Ringer solution, which was measured in each cell. Fitted curve represents the Hill equation with K_d= 62.3 mm and n = 3.24, with minimum rate constrained to zero and a maximum normalized rate of 1.15, fitted by a weighted Marquardt–Levenberg least squares algorithm.