The concentration of intracellular calcium ion ([Ca2+](i)) was altered in the same hair cell dissociated from a chick cochlea by the intrapipette perfusion technique. At a membrane potential of -40 mV, the elevation of [Ca2+](i) generated outward-going currents within 60 sec when the intrapipette solution was based on KCl. In controls, at membrane potentials more positive than -50 mV, outward K+ currents were observed and at large positive potentials, the outward K+ current decreased, showing an N-shaped I-V relationship. This outward K+ current was increased by elevation of [Ca2+](i) and was partially suppressed by a TEA-containing extracellular solution. We suggest that the Ca2+ increased by the intrapipette perfusion technique operates directly inside the cell membrane and activates Ca2+- activated K+ currents.
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