EFFECT OF TEMPERATURE ON ELECTRICAL RESONANCE IN LEOPARD FROG SACCULAR HAIR-CELLS

Effect of temperature on electrical resonance in leopard frog saccular hair cells. J. Neurophysiol. 79: 312-321, 1998. Leopard fro:: saccula r hair cells exhibit an electrical resonance in response to a depolari zing stimulus that has been proposed to contribute to the tuning prope rties of the frog sacculus by acting as an electrical band-pass filter . With the whole cell patch-clamp technique, we have investigated the effect of temperature on electrical resonances in isolated saccular ha ir cells, and we have described the effects of temperature on the curr ents and channel kinetics underlying electrical resonance. A hair cell 's onset resonant frequency in response to a constant depolarizing cur rent pulse increases linearly with temperature at a rate of 11 Hz/1 de grees C, exhibiting a mean Q(10) of 1.7 between 15 and 35 degrees C. H owever, offset resonant frequencies continue to double every 10 degree s C, exhibiting a mean Q(10) of 2.1. If steady-slate voltage during th e stimulus is held constant, all oscillatory frequencies increase with a mean Q(10) of 2.1. The average level of steady-state depolarization during a +150-pA depolarizing current pulse decreases with increasing temperature(-6 mV from 15 to 25 degrees C). This temperature-dependen t reduction of the steady-state membrane potential causes a shift in t he voltage-dependent channel kinetics to slower rates, thus reducing t he apparent Q(10) for onset resonant frequencies. The peak outward tai l current and net steady-state outward current, which is the sum of a voltage-dependent inward calcium current (I-Ca) and an outward calcium -dependent potassium current (I-K(Ca)), increase with temperature. exh ibiting a mean Q(10) of 1.7 between 15 and 25 degrees C. The activatio n rate (T-1/2) of the outward current exhibits a mean Q(10) of 2.3 bet ween 15 and 25 degrees C, while the deactivation rate (tau(rel)) exhib its a mean Q(10) of 2.9 over the same temperature range. These results support previous models of the molecular determination of resonant fr equency, which have proposed that a combination of I-K(Ca) channel kin etics and the overall magnitude of the outward current are primarily r esponsible for determining the resonant frequency of an isolated hair cell, The robust temperature sensitivity of the hair cell receptor pot ential contrasts sharply with the temperature-insensitive tuning prope rties of in vivo saccular nerve fiber recordings. Possible explanation s for this discrepancy are discussed.