Cation transport and membrane morphology

Abstract

Summary. Freeze-fracture electron-microscopy has been used to study membrane ultrastructure in (1) red cells from five species of mammals which have naturally occurring differences in cation transport and (2) red cells which have been treated with various drugs known to affect transport. A reproducible method for estimation of the intramembrane particle density is described. Considerable differences in the densities of intramembrane particles on the A-fracture faces were noted in five species of red cells studied. Such differences were not noted on the B-fracture faces. The differences correlated with species differences in active potassium transport and membrane phospholipid composition. Ouabain and trinitrocresolate-treated red cell membranes were found to have small but reproducible reductions in intra-membrane particle densities on the B-fracture faces, but such differences were not seen in valinomycin and amphotericin B-treated red cells. It was found that dimethylsulfoxide (DMSO) and glycerol drastically reduced intra-membrane particle densities. However, over the range of glycerol and DMSO concentrations in which membrane morphology was altered, no effects on either passive or active potassium transport were observed. It appears that the particles which are altered by DMSO and glycerol are not involved in cation transport. This paper reports experiments designed to explore the relation between ion transport and membrane ultrastructure as revealed by freeze-fracture electron-microscopy. We have directed particular attention to the intra~ membrane particles revealed by this method (Branton, 1966). We have used three approaches to this problem. First, we have examined the ultrastructure of the membranes of red cells from two genotypes of sheep and four other species of mammals known to have different red cell cation transport systems

Anion transport and membrane morphology

“…Above this concentration the passive permeabilities were increased several-fold. These results confirm those reported earlier for sheep red cells (Kirk & Tosteson, 1973). In contrast to chloride transport, alkali cation fluxes were unaltered at concentrations which reduced the B face intramembrane particle density and were increased at high concentrations.…”

“…This is similar to the previously reported effect of DMSO and glycerol on sheep erythrocytes (Kirk & Tosteson, 1973). The particle density on fracture face B, which is adjacent to Table 1.…”

“…This control solution was used for both the particle counts and the flux measurements to avoid any interference of phosphate on these measurements (see Kirk & Tosteson, 1973). Deuticke (1967) has shown that chloride inhibits phosphate transport and the converse relation may be expected (Gunn, 1972).…”

“…The procedures used previously (Kirk & Tosteson, 1973) were followed for preparation of samples, freeze-fracturing and measuring membrane particle densities. These procedures were found to give reproducible values of particle densities within experiments and between experiments.…”

“…Previously in this laboratory it was shown that there was little or no relationship between the loss of intramembrane pa,rticles caused by dimethylsulfoxide (DMSO) or glycerol and changes in passive or active transport of alkali cations in sheep erythrocytes (Kirk &Tosteson, 1973). Small but reproducible reductions in the intramembrane particle density, however, were found in membranes treated with ouabain or trinitrocresol which, respectively, inhibit and enhance Na + and K + transport.…”