Ion channels that mediate and/or modulate Acetylcholine (ACh) release at the transient efferent-inner hair cell (IHC) synapse during neonatal development.

GRACIELA KEARNEY; JAVIER ZORRILLA DE SAN MARTÍN; CAROLINA WEDEMEYER; ANA BELÉN ELGOYHEN; ELEONORA KATZ

Huerta Grande

Congreso; XXVIII Congreso Anual de la Sociedad Argentina de Investigación en Neurociencias; 2013

Sociedad Argentina de Investigación en Neurociencias

Inner hair cells are innervated by medial olivocochlear (MOC) fibers since birth to the onset of hearing (postnatal day (P) 12). At P9-11 ACh release is supported by both P/Q and N-type voltage-gated Ca2+ channels (VGCC) and negatively regulated by L-type VGCC, coupled to the activation of BK channels (Zorrilla de San Martín et al., 2010). We have previously reported that at P5-7, P/Q- but not N-type VGCC partially support ACh release at this synapse and that BK channels exert a negative control on release. Our present goal is to determine which other type/s of VGCCs mediate ACh release at this stage and whether L-type VGCCs are coupled to the activation of BK channels. Postsynaptic responses were monitored in whole-cell voltage-clamped IHCs while electrically stimulating the efferent fibers in P5-7 mouse cochleas. Surpirsingly, Nifedipine and Bay-K, an L-type VGCC antagonist and agonist, respectively, significantly enhanced the quantal content (m) of release (%increase = 161±21, 3 μM Nife; 294±26, 10 μM Bay-K), suggesting that L-type VGCC might be both triggering release and activating BK channels. However, preliminary occlusion experiments show that Bay-K has no effect on m after blocking BK channels with iberiotoxin (Ibtx) (m = 0.95, control; 2.7, Ibtx; 2.8, Ibtx + Bay-K). Moreover, Ibtx has no effect on m after incubation with L-type VGCC modulators (m = 0.8 ± 0.2 control; 2.49 ± 0.03 Nife; 2.9 ± 0.05 Nife+Ibtx; m = 0.7 ± 0.19 control; 1.9 ± 0.31 Bay-K; 2.1 ± 0.57). Our results show that at P5-7 L-type VGCC are also functionally coupled to BK channels. However, more experiments should be done to elucidate the paradoxical effect of Bay-K at this stage.