Stimulus‐related potassium changes in the organ of Corti of guinea‐pig.

Abstract

SUMMARY1. Potassium concentration was measured with double-barrelled K+-selective microelectrodes within the organ of Corti in the first turn of the guinea-pig cochlea.2. Penetration of the electrode from scala tympani through the basilar membrane was accompanied by an increase in K+ resting level from 3 0 mmol/l in perilymph to 3-4 mmol/l in cortilymph (n = 8). K+ resting level was not significantly different in various extracellular regions of the organ of Corti. On penetration of the cuticular plate, the K+ level reached 140 mmol/l simultaneously with the occurrence of a + 80 mV endocochlear potential. Impalement of hair cells and supporting cells was accompanied by an increase in K+ level, but intracellular K+ level was not systematically measured.3. Stimulation with pure tones over the frequency range 500 Hz to 25 kHz produced changes in the K+ level in the organ of Corti. The magnitude of these changes was dependent on stimulus frequency and intensity. At high sound intensities the K+ level in the tunnel of Corti could increase by typically 1 mmol/l, while a maximum increase of 3 mmol/l with respect to the resting level was observed immediately adjacent to inner hair cells.4. During brief exposures to moderate intensity, pure tone acoustic stimulation (10 s, < 80 dB SPL (sound pressure level)) of frequency 4 kHz or greater the K+ level in the extracellular fluid of the organ of Corti rose monotonically to a steady peak level. On cessation of the stimulus the K+ level fell monotonically with a time constant of about 2 s to a level close to the pre-stimulus level. In some cases this level was slightly above the pre-stimulus level.5. For brief exposures to moderate intensity sound (10 s, < 80 dB SPL) the extracellular potential in the organ of Corti became more positive. The amplitude of this sound-evoked change adapted during stimulation to a level approximately onefifth of its initial value. Upon cessation of the stimulus the potential fell transiently below its pre-stimulus level, before recovering to that level. The time constant of these changes was between 2 and 3 s. B. M. JOHNSTONE AND OTHERS6. Iso-response tuning curves for the sound-evoked elevation in K+ level in the organ of Corti in animals in good condition were similar to iso-rate tuning curves for primary afferent fibres reported previously. High-frequency slopes of tuning curves ranged from 130 to 260 dB/octave, while low-frequency slopes ranged from 40 to 60 dB/octave. Maximum Qlo dB values of 10 were measured.7. Input-output functions relating sound intensity to the amplitude of soundevoked changes in K+ level and the extracellular potential in the tunnel of Corti were linear for frequencies below the most sensitive frequency and non-linear at and above that frequency.8. Stimulation with loud sound (12 kHz, 105 dB SPL, 30 s), resulted in an initial 1 mmol/l increase in the K+ level in the extracellular space of the organ of Corti. During stimulation this elevated K+ concentration decreased, and after stimulation an 'undershoot' in resting l...

Perilymphatic potassium changes and potassium homeostasis in isolated semicircular canals of the frog.

“…In addition to dark cells, also glial, but mainly supporting cells, might be of importance in preventing perilymphatic accumulation of K+, especially in the narrow clefts surrounding hair cells. Studies on the cochlea (Johnstone, Patuzzi, Syka & Sykova, 1989), on the central nervous system (Sykova & Orkand, 1980) and on the retina (Coles & Orkand, 1983) support this idea. Glial, and possibly also supporting cells, in fact can operate as K+ stabilizers.…”

The Membrane Properties of Cochlear Root Cells are Consistent with Roles in Potassium Recirculation and Spatial Buffering

“…Following hair cell transduction, the resting perilymphatic [K + ] is raised locally by as much as 3 mM (Johnstone et al 1989). The underlying Deiters' cells provide an essential homeostatic function by "siphoning" excess K + , preventing prolonged depolarization of the hair cell membrane potential (Boettger et al FIG.…”

“…During auditory transduction K + exits into the perilymph via voltage-gated channels in the basolateral membrane of hair cells (Johnstone et al 1989;Mammano and Ashmore 1996). Accumulation of K + in the vicinity of hair cells is prevented by transporters expressed by underlying epithelial supporting cells (Boettger et al 2002;Boettger et al 2003;Hibino and Kurachi 2006).…”

Medial Olivocochlear Efferent Reflex in Humans: Otoacoustic Emission (OAE) Measurement Issues and the Advantages of Stimulus Frequency OAEs

“…Another elicitor-induced reduction in OAE amplitude has been seen with very high rate clicks (maximum length sequences); this reduction is not due to efferents (Hine et al 1997) and may also be due to intrinsic cochlear processes and/or to suppression. The origin of the intrinsic cochlear processes that produce these effects is unknown but two classes of candidates can be suggested: (1) local changes in K + concentrations (Johnstone et al 1989) or levels of ATP, calcium, or other chemicals in the organ of Corti (Chen et al 1998) and (2) sound-evoked synaptic actions in the nonefferent neural network beneath OHCs in humans, particularly the reciprocal synapses on OHC which may be formed by processes from type II spiral ganglion cells (Thiers et al 2002a,b).…”