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.