The influence of increased intracellular calcium level on outer hair cell (OHC) electromotility was examined by means of transcellular electrical stimulation in a partitioning microchamber. Electromotile activity was measured before and after application of the calcium ionophore ionomycin, which promotes the inflow of extracellular calcium, as well as its release from intracellular calcium stores. The ionomycin solvent, dimethyl sulphoxide (DMSO), by itself elicited a significant decrease in the magnitude of OHC electromotility. The DMSO effect was counteracted by 10 μM ionomycin and was reversed by 50 μM ionomycin. The increase in electromotility is partially mediated by a calmodulin-dependent mechanism, since W7, a calmodulin antagonist, attenuated the 50 μM ionomycin-induced motility increase. Our results suggest that the electromotility magnitude increase in isolated OHCs due to ionomycin is a calcium/calmodulin-dependent phenomenon.
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