A Role of H+ Flux in Active Ca2+ Transport into Sarcoplasmic Reticulum Vesicles.1 I. Effect of an Artificially Imposed H+ Gradient on Ca2+ Uptake

Abstract

To ascertain the function of H⁺ flux in active Ca²⁺ transport into sarcoplasmic reticulum vesicles, the effect of pH gradient on Ca²⁺ transport was examined. A transient H⁺ gradient (inside-acidic) was imposed on K⁺-loaded sarcoplasmic reticulum vesicles with the aid of K⁺-H⁺ exchange driven by nigericin. This proton gradient was dessipated rapidly and concomitantly with ATP-driven Ca²⁺ transport. Under these conditions, the initial rate of the Ca²⁺ uptake was increased about 1.5-fold. The stimulation of Ca²⁺ uptake was completely lost when the pH gradient was cancelled with an uncoupler plus membrane permeable cation before Ca²⁺ uptake. These results are interpreted in terms of H⁺ efflux coupled with Ca²⁺ transport.