Nitric oxide influences potassium currents in inner hair cells isolated from guinea-pig cochlea.

Abstract Objective Nitric oxide (NO) is a diffusible second messenger, which regulates neurotransmission, serving as the principal endothelium-derived relaxing factor. NO also acts as an ion channel modulator. Nitric oxide synthase (NOS) has been identified in the inner ear, although its physiological role remains unclear. In the present study, the effects of NO onto K currents in inner hair cells (IHCs) were investigated. Methods IHCs were acutely isolated and K currents were recorded by conventional whole-cell voltage-clamp recordings. NO donors sodium nitroprusside (SNP) were applied directly to the cells. Results In 1 mM SNP solutions, the amplitude of outward K currents ( I K,f and I K,s ) reversely decreased; however, fast activation kinetics was preserved. In the current–voltage relationship curves, the maximal slope conductances were 53.2 nS and 44.2 nS in control solutions and 1 mM SNP solutions, respectively. At the membrane potential of +110 mV, the amplitudes of outward currents were 9.2 ± 2.9 nA in control solutions and 7.3 ± 2.7 nA in 1 mM SNP solutions, showing a significant difference. Conclusion NO acts as a K channel modulator in IHCs. A fast K current suppression may account for the high-frequency hearing impairment by the prevention of fast repolarization.