Fig. 13.

Current amplitudes increase with resonant frequency. A, Peak inward current was determined for oscillatory hair cells in an external medium containing 5 mm [Ba⁺²]_ext and 10 mm 4-AP, after first recording their resonant frequency at −53 mV in control solution (standard internal pipette solution). Peak barium currents occurred at approximately a mean potential of −23 ± 3 mV and were observed to be larger in hair cells exhibiting higher resonant frequencies. The data are plotted on a semi-log scale along with data for isolated hair cells of the turtle basilar papilla (open diamonds) taken from Art and Fettiplace (1987) to emphasize the similarities in I_Ba amplitude distribution exhibited by these two preparations. Both lines drawn by eye; solid line, frog AP; dotted line, turtle BP. B, Outward conductance amplitude, corrected for inward current amplitude, was calculated and plotted against the measured resonant frequency at −53 mV. For the cells included fromA, inward barium currents (−20 mV) were divided by 2.5 (see Results) to provide an estimate of the calcium current amplitude, and this value was subtracted from the measured steady-state outward current at −20 mV to produce an estimate of the total outward current amplitude (filled circles). In cells in which the calcium current was isolated using a TEA–4-AP cocktail (open circles), the calcium current amplitude at −20 mV was subtracted directly from the outward current amplitude at −20 mV. Both sets of data produce a similar description of the rise ing_K(Ca) amplitude with resonant frequency. Conductances rather than currents are presented here to correct for differences in external K⁺ concentrations; barium current experiments were performed in 5 mm[K⁺]_ext, and the TEA–4-AP experiments were performed in 2 mm[K⁺]_ext. Curve fit by eye.