Two types of voltage-dependent potassium channels in outer hair cells fromthe guinea pig cochlea

Cell-attached and cell-free configurations of the patch-clamp technique wer e used to investigate the conductive properties and regulation of the major K+ channels in the basolateral membrane of outer hair cells freshly isolat ed from the guinea pig cochlea. There were two major voltage-dependent K+ c hannels. A Ca2+-activated K+ channel with a high conductance (220 pS, P-K/P -Na = 8) was found in almost 20% of the patches. The inside-out activity of the channel was increased by depolarizations above 0 mV and increasing the intracellular Ca2+ concentration. External ATP or adenosine did not alter the cell-attached activity of the channel. The open probability of the exci sed channel remained stable for several minutes without rundown and was not altered by the catalytic subunit of protein kinase A (PKA) applied interna lly. The most frequent K+ channel had a low conductance and a small outward rectification in symmetrical K+ conditions (10 pS for inward currents and 20 pS for outward currents, P-K/P-Na = 28). It was found significantly more frequently in cell-attached and inside-out patches when the pipette contai ned 100 mu M acetylcholine. It was not sensitive to internal Ca2+ was inhib ited by 4-aminopyridine, was activated by depolarization above -30 mV, and exhibited a rundown after excision. It also had a slow inactivation on ense mble-averaged sweeps in response to depolarizing pulses. The cell-attached activity of the channel was increased when adenosine was superfused outside the pipette. This effect also occurred with permeant analogs of cAMP and i nternally applied catalytic subunit of PKA. Both channels could control the cell membrane voltage of outer hair cells.