Studies of ionic currents in the isolated vestibular hair cell of the chick.

The ionic currents in enzymatically isolated vestibular hair cells of the chick were studied by a whole‐cell‐clamp variation of the patch voltage clamp, and by single channel recording. At membrane potentials more negative than ‐80 mV the hair cell showed anomalous rectification, and at potentials more positive than ‐40 mV large outward K currents were observed in normal saline. The outward K current decreased at large positive potentials, showing an N‐shaped I‐V relation. The outward K current was carried mostly through the Ca‐activated K channel. K currents through the anomalous rectifier channel showed a decay in normal saline. This decay was eliminated reversibly in Na‐free saline when the isotonic KCl‐EGTA solution was used as the internal medium. However, a fast decay was still observed in Na‐free high‐K external solution when isotonic CaCl‐EGTA was used as the internal medium. An increase in [K]o decreased the decay rate of the inward K current. The single‐channel conductance of the anomalous rectifier channel was 50 pS in 160 mM‐K saline and 23 pS in 40 mM‐K saline. In 100 mM‐Ca, ‐Sr and ‐Ba salines a large inward current was observed. At positive potentials the inward current carried by Ca and Sr ions showed significant decay; the current became outward at large positive potentials. Since the decay of the inward current was eliminated when 100 microM‐quinine was added to the bathing medium, it was probably due to the activation of some Ca‐activated K conductance which remained even with isotonic CsCl‐EGTA internal medium. The activation kinetics of the Ca channel were studied in 100 mM‐Ba solution at low temperatures (9‐13 degrees C). From a comparison of the time constants of activation with the time constants of the tail currents, it was concluded that the Ca channel follows Hodgkin‐Huxley‐type m2 kinetics. A slow component that deviated from m2 kinetics was frequently observed at relatively large positive potentials. The steady‐state fluctuations of Ba current showed a power density spectrum reasonably well fitted by a sum of two Lorentzian functions. The spectrum has a low‐frequency component which indicates kinetics close to the macroscopic activation process of the Ca channel and a high‐frequency component that indicates very fast flickering kinetics operating in the Ca channel.