Proton permeability of sarcoplasmic reticulum vesicles.

The proton permeability of rabbit skeletal muscle sarcoplasmic reticulum vesicles was investigated by means of membrane potential measurements. Diffusion potentials were generated in sarcoplasmic reticulum vesicles, rat liver microsomes, and sarcoplasmic reticulum phospholipid vesicles by transferring vesicles from low to high pH. Potentials were measured using the voltage-sensitive fluorescent dye 3,3'-dipentyl-2,2'-oxacarbocyanine. Diffusion potentials were generated readily in sarcoplasmic reticulum vesicles using H+ gradients. Generation of a similar potential in phospholipid vesicles or liver microsomes required the presence of an uncoupler of oxidative phosphorylation. H+ and K+ gradient competition experiments indicated that both K+,Na+-permeable and -impermeable sarcoplasmic reticulum vesicles were permeable to H+. These studies suggested that a mechanism of H+ transport exists in sarcoplasmic reticulum that is independent of the K,Na channel, and that transient or steady state membrane potentials may be effected by the movement of H+.