The relationship between valinomycin-induced alterations in membrane phospholipid fatty acid turnover, membrane potential, and cell volume in the human erythrocyte.

C A Dise,D B Goodman

doi:10.1016/s0021-9258(18)89445-5

Abstract

The relationship between alterations in transmembrane potential, cell volume, and phospholipid fatty acid turnover has been examined in human erythrocytes by treating the cells with the monovalent cation ionophore valinomycin. Valinomycin increases the cellular uptake of tetra[3H]phenylphosphonium ion by erythrocytes, indicating membrane hyperpolarization, and causes net loss of potassium chloride and water from the cells leading to a decrease in cell volume. Treatment of erythrocytes with valinomycin also enhances incorporation of [9, 10-(3)H]oleic acid into phospholipids, primarily diacylphosphatidylethanolamine. After replacing intracellular chloride with sulfate and treating cells with the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonate, exposure to valinomycin results in uptake of tetra[3H]phenylphosphonium ion and stimulation of [9, 10-(3)H]oleic acid incorporation, but, because anion efflux is prevented, no decrease in cell volume occurs. When tetra[3H]phenylphosphonium ion uptake is also prevented by suspending these cells in 125 mM KCl to dissipate the transmembrane potassium gradient, valinomycin still enhances [9, 10-(3)H] oleic acid incorporation into phospholipid. These results suggest that the presence of valinomycin in the membrane directly alters phospholipid fatty acid turnover and that some of the effects of this ionophore on cellular function previously attributed to alterations in transmembrane potential or cellular potassium content may instead be due to altered phospholipid turnover. Since it is possible that valinomycin may directly perturb phospholipid fatty acid turnover in other cells, the possibility that valinomycin-induced alterations in cellular function are due to altered phospholipid turnover rather than membrane hyperpolarization or altered potassium content should be considered in the interpretation of studies employing this ionophore.

Highlights

The relationship between alterations in transmem- brane lipid microviscosity and play an important role in brane potential, cell volume, and phospholipid fatty cellular activation in a variety of systems in which changes in acid turnover has been examined in human erythro- membrane function occur [1,2,3,4,5,6,7,8]
Because it is possible that the selective stimulation of fatty acid incorporation described previously isrelated to this hyperpolarization rather than toaltered cell volume,the effect of membrane hyperpolarization on fatty acid incorporation by human erythrocytes was approached more directly using valinomycin, a monovalent cation ionophoreselectivefor potassium whichhyperpolarizes the membranebecause it transports potassium as a charged complex [12]
Plasma and leukocytes by centrifugation (International Equipment Co., Model CL) a t 800 X g for 7 min at room temperature and washed Addition of valinomycin (10 PM) to human erythrocytes four times with 5 volumes of a buffer containing 140mM NaCl, 5 mM suspended in a buffer containing 5 mM KC1 induces rapid

Summary

Introduction

The relationship between alterations in transmem- brane lipid microviscosity and play an important role in brane potential, cell volume, and phospholipid fatty cellular activation in a variety of systems in which changes in acid turnover has been examined in human erythro- membrane function occur [1,2,3,4,5,6,7,8]. Uptake of [9,10-3H]oleicacid into the cellular free fatty acid and acyl thioester precursor pools is not increased in valinomycin-treated cells (Fig. 3).

Results

Conclusion