Effect of histamine on intracellular Ca2+ concentration in guinea pig isolated vestibular hair cells.

The present study examined the effects of histamine in the guinea pig isolated vestibular hair cells (VHCs) by measuring the dynamic changes of intracellular free calcium ion ([Ca2+]i) concentration using calcium sensitive dye Fura-2. The histamine-induced calcium response in VHCs was markedly increased at the concentration of 10 microM histamine in the presence of extracellular Ca2+, while in the absence of extracellular Ca2+, a slow increase of [Ca2+]i was evident. Receptor specificity of the response to histamine was examined: promethazine (H1 receptor antagonist), cimetidine (H2 receptor antagonist) and thioperamide (H3 receptor antagonist) completely blocked the histamine-induced calcium response at the concentrations of 2.5 microM, 1.0 microM and 1.0 nM, respectively. The responses were mediated by H1, H2 and H3 receptors and resulted in a rise of [Ca2+]i due to an influx of Ca2+ from the extracellular space and a release from intracellular stores. Our preliminary data suggest that under immuno-pathological conditions of the inner ear, histamine released from the mast cells distributed in the endolymphatic sac may act through receptors located on the vestibular hair cell membrane and may regulate the cell function and the signal transduction in the vestibular nerve-hair cell afferent system.