Ionic fluxes in rat uterine smooth muscle.

1. The K+, Na+ and Cl‐fluxes from the oestrogen‐stimulated rat uterine smooth muscle were measured using radioactive tracers. 2. The cellular compartment contained a concentration of K+ of 173‐6 mM which exchanged at a rate of 5‐9 x 10(‐12) mol.cm‐2.sec‐1. 3. Cl‐ exchanged at a rate of 6‐9 x 10(‐12) mol.cm‐2.sec‐1 from a cellular compartment having a concentration of 39‐3 mM. 4. The methods used for the evaluation of Na+ movements over‐estimate both influx and efflux values. If an average value of flux of 9‐2 x 10(‐12) mol.cm‐2.sec‐1 is considered we obtain PNa+/PK+ ratios of 2‐4 (‐42 mV) or 1‐3 (‐57‐6 mV), which are too high and do not correspond to electrophysiological evidence. 5. The relative permeabilities PCl‐/PK+ in the case of a membrane potential of ‐42‐0 mV could be 0‐8, or 1‐3 in the case of a membrane potential of ‐57‐6 mV. 6. Both conductances GK+ and GCl‐ seem to play an important role in determining membrane conductance.