Cell volume control in vestibular dark cells during and after a hyposmotic challenge

Cell height was measured as an index of volume in a preparation of vestibular dark cells in which the perfusate had access to both sides of the epithelium. In response to a hyposmotic challenge induced by removal of 75 mM NaCl, cell height increased to 107%; however, cell width did not increase. Significantly larger increases in cell height were observed in the absence of Cl- or K+ or in the presence of ouabain, lidocaine, barium, or quinidine, at 7 degrees C, or after fixation with glutaraldehyde. However, no significantly different swelling was observed during a hyposmotic challenge in the absence of Na+ or in the presence of bumetanide or ethoxyzolamide. Subsequent return to control osmolarity caused a regulatory volume increase that was dependent on Na+, Cl-, and K+, inhibited by bumetanide, ouabain, or 7 degrees C, however not inhibited by ethoxyzolamide, barium, quinidine, or lidocaine. The data suggest that cell volume control during the hyposmotic challenge involved a mechanism dependent on cytosolic KCl and the Na(+)-K(+)-ATPase and that the Na(+)-Cl(-)-K+ cotransporter was involved in regulatory volume increase.