CHOLINERGIC RESPONSES IN DEVELOPING OUTER HAIR-CELLS OF THE RAT COCHLEA

Acetylcholine-evoked currents were investigated using the conventional whole-cell patch-clamp recording technique in developing outer hair c ells (OHCs). The cells were isolated from the rat cochlea at different stages of postnatal development ranging from day 4 (P4) to P30. Acety lcholine-evoked currents could be recorded at P6 and P8. At this devel opmental stage, the majority of OHCs displayed inward nicotinic-like c urrents near the resting membrane potential. These cholinergic current s zeroed near 0 mV, as expected for a non-selective cation current, an d could be reversibly blocked by d-tubocurarine. At P12 and adult stag e, the cholinergic response of OHCs switched to an outward current rev ersing near E(K) and displaying a bell shape peaking between -40 and - 30 mV. This change in polarity of the acetylcholine response during po stnatal development might be explained by progressive functional coupl ing between acetylcholine ionotropic receptors permeable to Ca2+ and n earby Ca2+-activated K+ channels at the synaptic pole of OHCs.