VOLUME REGULATION IN GUINEA-PIG OUTER HAIR-CELLS AND THE ROLE OF INTRACELLULAR CALCIUM

Single outer hair cells (OHCs) isolated from the guinea pig cochlea showed a regulatory volume decrease (RVD) after the initial cells swelling despite continued exposure to a hypotonic solution. The accompanying change of the intracellular Ca2+ concentration ([Ca2+]i) in the OHCs was investigated using the Ca2+-sensitive dye fura-2. Hyposmotic activation led to a [Ca2+]i increase which was accompanied by cell shortening and swelling. In a nominally Ca2+-free solution, however, [Ca2+]i was not significantly increased during hyposmotic activation although shortening and swelling of the OHCs were observed. These results suggest that the increase in [Ca2+]i during hyposmotic activation is mainly based on an influx of extracellular Ca2+.