Hyposmotic activation hyperpolarizes outer hair cells of guinea pig cochlea.
The electrophysiological responses of isolated guinea pig outer hair cells (OHCs) to hyposmotic activation were studied using the whole-cell patch-clamp technique. The cell swelling by hyposmotic activation hyperpolarized OHCs by 6.6 +/- 2.3 mV from the resting membrane potential of -58.5 +/- 5.9 mV (n = 48). This hyperpolarization was associated with an outward current (97.7 +/- 22.2 pA, n = 15). The hyperpolarization was inhibited by 300 microM quinine, 5 mN Ba2+ and increasing the extracellular K+ to 30 mM from 5 mM. In the absence of extracellular Ca2+ (1 mM EGTA), the hyperpolarization during hyposmotic activation was also abolished while the following depolarization was preserved. 50 microM GdCl3, which is known to block stretch-activated non-specific cation channels, inhibited the hyperpolarization reversibly. 50 microM GdCl3 also inhibited [Ca2+]i increase during hyposmotic activation as shown by the calcium-sensitive dye fura-2. Simultaneously, the [Ca2+]i increase and the hyperpolarization during hyposmotic activation could be observed using the combined method of whole-cell patch clamp and fura-2 technique. It is concluded that the cell swelling by hyposmotic activation may activate the stretch-activated non-specific cation channels in the OHCs which allow a Ca2+ influx. In turn, this [Ca2+]i increase leads to an activation of the Ca(2+)-activated K+ channels at the basolateral membrane of OHCs which results finally in a reversible hyperpolarization of OHCs by K+ efflux.
Harada
N
N
Hearing Research Laboratories, Department of Otolaryngology, University of Tübingen, Germany.
Ernst
A
A
Zenner
H P
HP
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D003051:Cochlea / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D016257:Fura-2; D005682:Gadolinium / Q000494:pharmacology; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology
D001464:Barium; D011803:Quinine; D005682:Gadolinium; D011188:Potassium; D002118:Calcium; D016257:Fura-2