The cholinergic response of inner hair cells is correlated with expression of the alpha 10 nicotinic subunit.

KATZ E; GLOWATZKI, E; VETTER, DE; GÓMEZ-CASATI, ME; ELGOYHEN, AB; FUCHS PA

Daytona Beach, FL, USA

Congreso; The Association for Research in Otolaryngology, midwinter meeting; 2003

In the developing mammalian cochlea, inner hair cells (IHC) are transiently innervated by efferent fibers. This synapse is inhibitory and mediated by a nicotinic cholinergic receptor (nAChR) probably formed by the alpha9 and alpha10 subunits. Expression of alpha9 mRNA persists in the adult IHC, while alpha 10 does not. We have characterized cholinergic input to IHC during this developmental transition. We used whole cell recordings of IHC in acutely excised apical turns of the rat organ of Corti spanning the onset of hearing (P12). At a holding potential of –90 mV, ACh elicited inward currents (-449 pA) in 8 of 8 IHC at P7-9 and 5 of 5 cells exhibited efferent synaptic currents upon K+ depolarization. At P10-12, ACh elicited currents of –264 pA (16 of 16) and 14 of 15 IHC had efferent synaptic currents. At P13-14, ACh elicited currents of smaller amplitude (-29 pA) in 3 of 5 IHC and efferent synaptic currents appeared in 2 of 4 cells. By P18, only 1 of 6 IHC responded to ACh and 0 of 10 cells tested had efferent synaptic currents. In situ hybridization was used to show alpha10 expression in IHC at P3. alpha 10 expression in IHCs decreased at P13, and by P21 was undetectable. The correlation of cholinergic sensitivity with subunit expression strengthens the hypothesis that the functional IHC cholinergic receptor is composed of both the alpha9 and alpha10 subunits.