Regulation of cellular volume in rat myometrium

1.1. Pieces of rat myometrium that had been made Na+-rich by incubation in K+-free medium at 4 °C, subsequently lost weight and extruded Na+ and water on being rewarmed at 37 °C. In the present study the mechanism of these changes was examined.2.2. The process was not dependent on the coupled Na+-K+ pump since it was not abolished by omission of K+ or by absence of external Na+. It was however abolished by metabolic inhibition, produced by anaerobiosis and omission of d-glucose from the medium.3.3. Shrinkage on rewarming was not Na+ dependent, since Na+ could be replaced by K+ or Li+. Shrinkage was prevented when Cl± was replaced by an impermeant anion, e.g. propionate or methylsulphate.4.4. In the absence of Ca2+, shrinkage did not occur. The process was also inhibited by iodoacetamide, isopropylnoradrenaline and papaverine.5.5. The results are compatible with a mechanochemical mechanism for the ouabain-insensitive control of cell volume. It is possible that water and Na+ extrusion result from an alteration in ion binding in, and subsequent contracture of, micropinocytotic vesicles. It is also possible that with cooling the plasma membrane undergoes a phase transition with resultant loss of volume control.