Intracellular calcium changes by hyposmotic activation of cochlear outer hair cells in the guinea pig

During continued exposure to a hypotonic solution, isolated outer hair cells (OHCs) from the guinea pig cochlea showed a regulatory volume decrease (RVD) after initial cell swelling. In the absence of extracellular Ca2+, RVD was significantly inhibited. Using Ca(2+)-sensitive dye fura-2, accompanying changes of the intracellular Ca2+ concentrations ([Ca2+]i) of OHC were investigated. Hyposmotic activation resulted in a [Ca2+]i increase associated with cell shortening and swelling. In a Ca(2+)-free solution, [Ca2+]i was not significantly increased during hyposmotic activation although shortening and swelling of the OHC was observed. These results suggest that the increase in [Ca2+]i during hyposmotic activation is mainly based on an influx or extracellular Ca2+ which precedes the RVD.