Localized calcium signals in inner hair cells of the developing inner ear following efferent fiber stimulation.

MARCELO J. MOGLIE; A. BELEN ELGOYHEN; JUAN D. GOUTMAN

Huerta Grande, Cordoba

Congreso; XXIX Congreso Anual Sociedad Argentina de Investigación en Neurociencia.; 2014

Efferent cholinergic neurons project from the brainstem to inhibit outer hair cells (OHC) of the mammalian inner ear. This inhibitory synapse combines the entry of calcium through α9α10 nicotinic receptors with the activation of nearby SK2 calcium-dependent potassium channels to hyperpolarize the hair cell. The presence of a thin near-membrane cistern that is co-extensive with the efferent terminal contacts, presenting both ryanodine receptors and calcium pumps, let us hypothesize that it may play a role in calcium homeostasis. Before the onset of hearing (postnatal day 12 in mice) inner hair cells (IHCs) are transiently innervated by efferent fibers and exhibit the same cisterns juxtaposed to synaptic contacts. By electrically stimulating this fibers and recording IPSCs combined with calcium imaging techniques, we measured calcium influx to hair cells during efferent activation of the nicotinic receptors. We found a localized increase in calcium signals temporally coincident with the activation of the nicotinic receptor. Between two and three calcium hotspots were found in each cell, presenting a calcium signal intensity that correlates with the amplitude and kinetics of the IPSCs. Consequently, minimal and maximal stimulation experiments exhibited three different levels of activity. Thus, we suggest that multiple and independent efferent synaptic contacts are present in a single IHC.