The Effect of Temperature on Electrical Resonance in Leopard Frog Saccular
Hair Cells.
M.S. Smotherman and P.M. Narins.
Department of Physiological Science, The University of California, Los
Angeles, CA 90095.
APStracts 4:262N, 1997.
ABSTRACT
Leopard frog saccular hair cells exhibit an electrical resonance in response
to a depolarizing stimulus which has been proposed to contribute to the tuning
properties of the frog sacculus by acting as an electrical band-pass filter.
Using the whole-cell patch-clamp technique we have investigated the effect of
temperature on electrical resonances in isolated saccular hair cells, and we
have described the effects of temperature on the currents and channel
kinetics underlying electrical resonance. A hair cell's onset resonant
frequency in response to a constant depolarizing current pulse increases
linearly with temperature at a rate of 11 Hz/1øC, exhibiting a mean Q10 of 1.7
between 15 and 35øC. However, offset resonant frequencies continue to double
every 10øC, exhibiting a mean Q10 of 2.1. If steady-state voltage during the
stimulus is held constant, all oscillatory frequencies increase with a mean
Q10 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 25øC). This temperature-dependent reduction of the steady-state
membrane potential causes a shift in the voltage-dependent channel kinetics to
slower rates, thus reducing the apparent Q10 for onset resonant frequencies.
The peak outward tail current and net steady-state outward current, which is
the sum of a voltage-dependent inward calcium current (Ica) and an outward
calcium-dependent potassium current (Ik(ca)), increase with temperature,
exhibiting a mean Q10 of 1.7 between 15 and 25øC. The activation rate (T1/2)
of the outward current exhibits a mean Q10 of 2.3 between 15 and 25øC, while
the deactivation rate (_rel) exhibits a mean Q10 of 2.9 over the same
temperature range. These results support previous models of the molecular
determination of resonant frequency, which have proposed that a combination of
Ik(ca) channel kinetics and the overall magnitude of the outward current are
primarily responsible for determining the resonant frequency of an isolated
hair cell. The robust temperature sensitivity of the hair cell receptor
potential contrasts sharply with the temperature-insensitive tuning properties
of in vivo saccular nerve fiber recordings. Possible explanations for this
discrepancy are discussed.
Received 25 March 1997; accepted in final form 11 September 1997.
APS Manuscript Number J252-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997