The Journal of Neuroscience, July 1, 1999, 19(13):5275-5292
The Electrical Properties of Auditory Hair Cells in the Frog
Amphibian Papilla
Michael S.
Smotherman and
Peter M.
Narins
Department of Physiological Science, The University of California,
Los Angeles, California 90095-1527
The amphibian papilla (AP) is the principal auditory organ of the
frog. Anatomical and neurophysiological evidence suggests that this
hearing organ utilizes both mechanical and electrical (hair cell-based)
frequency tuning mechanisms, yet relatively little is known about the
electrophysiology of AP hair cells. Using the whole-cell patch-clamp
technique, we have investigated the electrical properties and ionic
currents of isolated hair cells along the rostrocaudal axis of the AP.
Electrical resonances were observed in the voltage response of hair
cells harvested from the rostral and medial, but not caudal, regions of
the AP. Two ionic currents, ICa and
IK(Ca), were observed in every
hair cell; however, their amplitudes varied substantially along the
epithelium. Only rostral hair cells exhibited an inactivating potassium
current (IA), whereas an inwardly
rectifying potassium current (IK1)
was identified only in caudal AP hair cells.
Electrically tuned hair cells exhibited resonant frequencies from 50 to
375 Hz, which correlated well with hair cell position and the tonotopic
organization of the papilla. Variations in the kinetics of the outward
current contribute substantially to the determination of resonant
frequency. ICa and
IK(Ca) amplitudes increased with resonant
frequency, reducing the membrane time constant with increasing resonant
frequency. We conclude that a tonotopically organized hair cell
substrate exists to support electrical tuning in the rostromedial
region of the frog amphibian papilla and that the cellular mechanisms
for frequency determination are very similar to those reported for
another electrically tuned auditory organ, the turtle basilar papilla.
Key words:
hair cells; hearing; electrical tuning; electrical
resonances; frequency discrimination; frogs; Rana pipiens
pipiens; amphibian papilla; calcium currents; potassium
currents
Copyright © 1999 Society for Neuroscience 0270-6474/99/19135275-18$05.00/0
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