Ouabain-sensitive thallium fluxes in smooth muscle of rabbit uterus

1. Rabbit myometrium accumulates Tl in a time-dependent fashion and the majority of the uptake of Tl is ouabain-sensitive. 2. In normal chloride-containing media, the uptake of Tl, though ouabain-sensitive, is less than in chloride-free media and this difference is due to a greater ouabain-insensitive uptake. 3. The ouabain-insensitive uptake in normal chloride-containing media is reduced by furosemide and furosemide also reduces total uptake in this solution. In chloride-free media, however, furosemide is without effect on total or ouabain-sensitive uptake. 4. In chloride-free media, the uptake of Tl against Tl concentration is sigmoidal, suggesting that more than one Tl ion is being transported at a time. 5. Tl was capable of substituting for K in electrogenic Na pumping; it was approximately twice as effective as K and the inhibitory effect of Tl was blocked by ouabain. 6. Tl efflux can be explained by a simple two-compartment model in both normal and chloride-free solutions. 7. The uptake of Tl was inhibited by alkali cations with the order of potency being Tl+ > K+ > Rb+ > Cs+ at 10 mM and Tl+ > K4 = Rb+ > Cs+ at 5 mM ion concentrations. 8. It is concluded that Tl enters the smooth muscle of rabbit uterus by diffusion, active ouabain-sensitive transport and active chloride- and furosemide-sensitive transport.