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

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

Huerta Grande

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

Sociedad Argentina de Investigación en Neurociencias

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 the activation of BK channels. We have recently reported that at P5-7, P/Q- and R-type but not N-type VGCC support ACh release and that BK channels exert a negative control. Surprisingly, both the L-type VGCC antagonist nifedipine and the agonist Bay-K enhanced the quantal content of release (m). To further elucidate the role of L-type and N-type VGCC at P5-7, we analyzed the frequency of spontaneous inhibitory synaptic currents (IPSCs) in whole-cell voltage-clamped IHCs bathed in high K+ solution in the presence of Nifedipine, Bay K and ω-CgTx. 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 channels are involved in this type of 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, electrically-evoked IPSCs were monitored in whole-cell voltage-clamped IHCs in P3 cochleas. ω-AgaIVA did not affect m (120,80±9,21%; n=3; p>0,05), suggesting that P/Q-type VGCC do not support release at this early stage. Bay-K enhanced m by 382±120% (n=2), suggesting that L-type VGCCs support release at P3. Our results show there are significant changes in the VGCC that support and/or modulate ACh release at the MOC-IHC synapse during development.