Effect of salicylate on KCNQ4 of the guinea pig outer hair cell

Salicylate causes a moderate hearing loss and tinnitus in humans at high-dose levels. Salicylate-induced hearing loss has been attributed to impaired sound amplification by outer hair cells (OHCs) through its direct action on the OHC motility sensor and/or motor. However, there is a disparity of salicylate concentrations between the clinical and animal studies, i.e., extremely high extracellular concentrations of salicylate (from 1 to 10 mM) is required to produce a significant reduction of electromotility in animal studies. Such concentrations are above the clinical/physiological range for humans. Here, we showed that clinical/physiological concentration range of salicylate caused concentration-dependent and reversible reductions in I _K,n (KCNQ4) and subsequent depolarization of OHCs. Salicylate reduced the maximal tail current of the activation curve of I_K,n without altering the voltage-sensitivity (V_half). The salicylate-induced reduction of I_K,n was almost completely blocked by linopirdine (0.1 mM) and BaCl2 (10 mM). Consistent with the finding in OHCs, salicylate significantly reduced KCNQ4-mediated current expressed in Chinese hamster ovarian (CHO) cells by comparable amplitude to OHCs without significantly shifting V_half. Nonstationary fluctuation analysis shows that salicylate significantly reduced the estimated single-channel current amplitude and numbers. Intracellular Ca²⁺ elevation resulting from cytoplasmic acidosis also contributes to the current reduction of I_K,n (KCNQ4) of OHCs. These results indicate a different model for the salicylate-induced hearing loss through the reduction of KCNQ4 and subsequent depolarization of OHCs, which reduces the driving force for transduction current and electromotility. The major mechanism underlying the reduction of I_K,n (KCNQ4) is the direct blocking action of salicylate on KCNQ4.