Nature of Electrolyte Exchange in Isolated Uterine Smooth Muscle.

KAO, C. Y ., AND M. J. SIEGMAN. Nature of electrolyte exchange in isolated uterine smooth muscle. Am. J. Physiol. 205(a): 674-680. Ig63.Data are presented to show the marked changes in contents of water, sodium, potassium, and chloride in isolated rabbit myometrial strips when these preparations are incubated in Krebs-bicarbonate solution. The changes are interpreted to be composed of an initial passive redistribution and a later active transport phase. In support of this interpretation are: r) in the passive redistribution phase, the intracellular ionic concentrations approached those in the medium, and 2) at o C, only passive redistribution was present, while at 25 and 37 C, restoration towards the normal ionic distribution, i.e., active transport, also occurred. Movement of water is largely isotonic and movement of chloride appears to be largely passive. Much potassium is actively accumulated in excess of the amount required by Donnan distribution. In contrast to the estrogendominated myometrium, the progesterone-dominated myometrium showed a lesser extent of passive redistribution and an earlier appearance of active transport phenomena. In both types of myometrium the net amounts of sodium extruded and potassium reaccumulated are balanced, as are the rates of the reciprocal net movements.