Control of sodium fluxes in Mycoplasma gallisepticum

Swelling of Mycoplasma gallisepticum cells when incubated in a glucose-free isoosmotic NaCl buffer was shown to be due to the entrance of NaCl into the cell. Volume regulation therefore depends on Na+ extrusion. The mechanism of Na+ extrusion in cells and proteoliposomes, prepared from M. gallisepticum membrane fragments, was investigated by following both 22Na+ efflux and pH changes. Our results indicate that Na+ is expelled from cells via two separate mechanisms, an Na+/cation exchange mechanism and an Na+-ATPase. The possible association of these mechanisms with K+ accumulation is suggested.