Simultaneous monitoring of slow cell motility and calcium signals of the guinea pig outer hair cells

'Slow' motility (shape changes over seconds to minutes) of the mammalian cochlear outer hair cell (OHC) could play a protection role from intense sound pressure and is associated with elevation of the cytosolic free Ca2+ concentration ([Ca2+](i)). In the present work, a new approach was elaborated using fluorescent imaging for continuous monitoring of both [Ca2+](i) changes and slow motility of OHCs employing the Ca2+ fluorescent indicator Fura-2. Whole OHC fluorescence and that of cell segments were analyzed to discriminate between fluorescence changes caused by [Ca2+](i) rise and those related to change of the cell shape. The reliability of the method was examined by simultaneous monitoring of [Ca2+](i) and OHC length changes induced by change of buffer osmolarity or by increase of KCl concentration. The method revealed that the time course of [Ca2+](i) increase and rate of cell shortening often do not coincide. It was also observed that [Ca2+](i) increased in 70 mM KCl more slowly than the rate of KCl delivery to OHCs. The comparison of the time courses of [Ca2+](i) elevation, induced by increase of K+/Na+ ratio and by substitution of Na+ with N-methyl-D-glucamine(+), indicated that the relatively slow kinetics of [Ca2+](i) increase in the OHC is partially attributed to regulation of Ca2+ homeostasis by the Na+/Ca2+ exchanger. (C) 2000 Elsevier Science B.V. All rights reserved.