Action of salicylate on membrane capacitance of outer hair cells from the guinea‐pig cochlea.

Abstract

1. The effect of salicylate on membrane capacitance and intracellular pH has been measured in isolated outer hair cells (OHCs) during whole cell recording. Cell membrane capacitance was measured using a lock-in amplifier technique. 2. Salicylate applied in the bath reduced the fast charge movement, equivalent to a voltagedependent membrane capacitance, present in OHCs. Simultaneous measurement of membrane capacitance and voltage-driven cell length changes showed that salicylate reduced both together. 3. A small effect of salicylate on outward currents at 0 mV was observed. Sodium salicylate (5 mM) reduced the currents by 19% and another weak acid, sodium butyrate (10 mM), reduced outward currents in OHCs by 15%. 4. The ratiometric dye 2,7-bis(2-carboxymethyl)-5,6-carboxyfluorescein (BCECF) was used to measure pH, changes in OHCs during weak acid exposure. Membrane capacitance and pH1were measured simultaneously in OHCs exposed first to 10 mm sodium butyrate and then to 5 mM sodium salicylate. Although both compounds produced a similar reduction in pH1, butyrate decreased the resting capacitance from a mean resting capacitance of 35 pF (at -30 mV) by 5±4 + 2-1 pF, whereas salicylate decreased it by 15-7 + 2-3 pF (n = 4). 5. Exposure of OHCs to 10 mm sodium benzoate, an amphiphilic anion, reduced resting membrane capacitance at -30 mV by 9-2 + 3-2 pF (n = 3). Outward currents, measured at 0 mV, were reduced by 0-25 + 0 05 nA during benzoate application, comparable with the effect of salicylate.6. Capacitance was measured during slow bath application of salicylate. The resulting dose-capacitance curve had a Hill coefficient of 3 40 + 0-85 (n = 4) and a half-maximal dose of 3.95 + 0 34 mm. The dose-capacitance curve was not significantly voltage dependent. 7. Salicylate had no detectable effect on the resting capacitance of Deiters' cells, a non-sensory cell type of the organ of Corti. 8. It is concluded that many of the described effects of salicylate on hearing may arise from the partitioning of the salicylate molecule into the membrane of the OHC and consequent inhibition of OHC motility.

Depolarization of Cochlear Outer Hair Cells Evokes Active Hair Bundle Motion by Two Mechanisms

“…In all cases, the block was irreversible, and some cell deterioration occurred with an increase in the leak current. The slow onset of block and the lack of reversibility, in contrast to the effects on dissociated OHCs (Tunstall et al, 1995;Kakehata and Santos-Sacchi 1996), may be partly attributable to the limited access on the basolateral surface of the hair cells in the intact epithelium.…”

“…However, it would be unwise to conclude that salicylate has a direct effect on the MET channels because the reduction in current may have resulted partly from a side effect, such as a drop in intracellular pH. Salicylate has been shown to acidify the cytoplasm (Tunstall et al, 1995), and an increase in intracellular H ϩ ions may have caused …”

“…The charge movements occurring during prestin activation were quantified by integrating the initial capacitive transient at the start of the voltage step (Tunstall et al, 1995). This integration was performed for the initial 1-2 ms after the voltage step in two separate ways: (1) by fitting an exponential to the onset of the ionic current, subtracting this fit from the total current, and integrating the resulting transient; and (2) by measuring the amplitude of the capacity transient and dividing it by the time constant of decay of the transient (see Fig.…”

“…OHC motility and the associated nonlinear capacitance are known to be blocked by Na salicylate (Shehata et al, 1991) with half-inhibition (K I ) in the millimolar range [K I of 4 mM (Tunstall et al, 1995); K I of 1.6 mM (Kakehata and SantosSacchi 1996)]. External perfusion with 10 mM Na salicylate produced a reduction in the hair bundle displacement and abolition of the nonlinear capacitance seen in the current transients at the start and end of the voltage step (Fig.…”

A Characteristic of Aspirin-Induced Hearing Loss in Auditory Brainstem Response of Conscious Rats.

“…There have been numerous investigations of the electrical activity in the cochlea or auditory nerve on a salicylate effect, e.g., cochlear microphonic (CM) [4,13,24,27,28,30], summating potential (SP) and endocochlear potential (EP) [27,30], compound action potential (CAP) of the auditory nerve [27,30,31] and suppression of active cochlear processes [21]. Recent results suggest that the effects of salicylate may arise from alterations in the membrane capacitance of the OHC and consequent inhibition of OHC motility [32]. Therefore, the cochlea appears to be the primary site of ototoxicity and salicylate's action within the cochlea may mainly involve the OHCs.…”