Mechanisms of Hair Cell Tuning

Abstract

Mechanosensory hair cells of the vertebrate inner ear contribute to acoustic tuning through feedback processes involving voltage-gated channels in the basolateral membrane and mechanotransduction channels in the apical hair bundle. The specific number and kinetics of calcium-activated (BK) potassium channels determine the resonant frequency of electrically tuned hair cells. Kinetic variation among BK channels may arise through alternative splicing of slo gene mRNA and combination with modulatory beta subunits. The number of transduction channels and their rate of adaptation rise with hair cell response frequency along the cochlea's tonotopic axis. Calcium-dependent feedback onto transduction channels may underlie active hair bundle mechanics. The relative contributions of electrical and mechanical feedback to active tuning of hair cells may vary as a function of sound frequency.

Seasonal plasticity of auditory saccular sensitivity in “sneaker” type II male plainfin midshipman fish, Porichthys notatus

“…Previous studies by Rohmann and Bass (2011) and Rohmann et al (2013) showed that the seasonal variation in the frequency sensitivity of saccular hair cells in type I males could be explained by seasonal changes in the abundance of calcium-activated potassium BK channels, which are known to be responsible for a large conductance, outward current that produces electrical receptor oscillations along the hair cell epithelium (Lewis and Hudspeth 1983;Roberts et al 1988;Fettiplace and Fuchs 1999). The electrical resonance that arises from the ion-channel current kinetics of hair cells is thought to be the major contributing factor that influences low-frequency (<1 kHz) hair cell tuning in reptiles and birds (Fettiplace and Fuchs 1999) and in fish Romero 1991, 1992). Rohmann et al (2013) showed that by using the BK channel antagonist iberiotoxin to reduce BK channel availability they could effectively induce a saccular neurophysiological phenotype similar to that found in non-reproductive type I males.…”

Inner ear morphological correlates of ultrasonic hearing in frogs

“…Soma lengths of mammalian outer hair cells (Bohne and Carr, 1985;Fettiplace and Fuchs, 1999), goldfish saccular hair cells (Sugihara and Furukawa, 1989) and frog AP hair cells (Simmons et al, 1994) decrease systematically with increasing frequency sensitivity along the auditory organ's tonotopic axis. Experiments with isolated frog AP hair cells demonstrate that whole-cell capacitances vary predictably with soma length, providing additional evidence that the hair cell's resonant frequency is inversely related to its length (Smotherman and Narins, 1999a, b).…”

“…Experiments with isolated frog AP hair cells demonstrate that whole-cell capacitances vary predictably with soma length, providing additional evidence that the hair cell's resonant frequency is inversely related to its length (Smotherman and Narins, 1999a, b). Bundle heights also negatively correlate with the frequency of maximal hair cell sensitivity in the mammalian cochlea (Lim, 1980;Fettiplace and Fuchs, 1999), and chick (Tilney and Saunders, 1983) and lizard basilar papillae (Mulroy, 1974;Turner et al, 1981).…”

“…The majority of mammalian species hears well into the ultrasonic range (i.e., >20 kHz) while other vertebrates possess comparatively limited sensitivity (Heffner and Heffner, 1998;Fettiplace and Fuchs, 1999;Dooling et al, 2000, but see Mann et al, 2001). Anuran amphibians (frogs and toads) are among the taxa that have been considered to possess restricted high-frequency hearing ability, with an upper detection limit of 5e8 kHz (Loftus-Hills and Johnstone, 1970).…”

“…In mammals, the advent of high-frequency sensitivity is attributed to key morphological innovations within the ear, including the extension of a flexible, mechanically tuned membrane on which the sensory receptors sit (i.e., the basilar membrane), and the specialization of inner ear supporting and sensory cell types (Fettiplace and Fuchs, 1999). These features are not present in frogs.…”