Inhibitory Effect of Sodium Pumping on Spontaneous Contractility of Rabbit Myometrium

Abstract

The effects of K⁺ and related cations on the spontaneous contractility of estrogen-dominated rabbit myometrial strips were examined in vitro with isometric force-displacement transducers. Addition of 5–40 mM KCl, RbCl, or CsCl caused increased contractility of strips in medium containing 5.4 mM K⁺. Removal of K⁺ from the medium generally increased contractility. Addition of KCl, RbCl, CsCl, or LiCl to strips in K⁺-free medium caused an immediate rapid inhibition of contractility, the relative potencies being K⁺ = Rb⁺ > Cs⁺ > Li⁺. This effect was produced by 0.25–40 mM KCl or RbCl and was inhibited by 10⁻⁵ M ouabain. It was concluded that addition of K⁺, Rb⁺, Cs⁺, or Li⁺ to tissues in K⁺-free medium probably activated electrogenic Na⁺ pumping with resultant membrane hyperpolarization and inhibition of mechanical activity.