Voltage-gated Ca2+ channels (VGCC) that support ACh release at the mouse efferent-inner hair cell synapse during early stages of development

KEARNEY, GI; ZORRILLA DE SAN MARTÍN, J.; WEDEMEYER, C; ELGOYHEN, A.B; KATZ, E.

Huerta Grande - Córdoba

Congreso; XXIX Congreso Anual de la Sociedad Argentina de Investigación en Neurociencias (SAN; 2014

Sociedad Argentina de Neurosciencias

Inner hair cells (IHC) 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 P/Q- and N-type VGCC and negatively regulated by L-type VGCC coupled to BK channels. We have reported that at P5-7, P/Q- and R-type but not N-type VGCC support release and that BK channels exert a negative control. Surprisingly, L-type VGCC agonists and antagonists Bay-K and nifedipine, respectively, enhanced ACh release. To further elucidate the role of L-type and N-type VGCC at P5-7, we analyzed the frequency of spontaneous inhibitory synaptic currents (sIPSCs) in whole-cell voltage-clamped IHCs bathed in high K+ solution. Nifedipine 3 μM decreased (25,85±8,44%, n=2) and Bay-K 10 μM increased (358,70±5,04%;n=2) sIPSC frequency, as expected if these VGCC mediate K+-evoked release. ω-CgTx 500 nM, had no effect on sIPSC frequency (control 2,86±0,65 Hz; n=5; ω-CgTx 3,06±0,06 Hz, n=3; p>0,05), confirming that N-type VGCC are not functionally expressed at P5-7. In addition, ω-AgaIVA did not affect the quantum content (m) (120,80±9,21%; n=3; p>0,05) of electrically-evoked IPSCs in IHCs from P3 cochleas, suggesting that P/Q-type VGCC do not support release at P3. Bay-K, however, enhanced m by 382±120% (n=2), suggesting that L-type VGCCs support release at this stage. These results show there are significant changes in the VGCC that support and/or modulate ACh release at the MOC-IHC synapse during development.