Modulation of red blood cell sugar transport by lyso-lipid

The in vitro presentation to red blood cells of specific lysolipids in amounts comparable to lysolipid levels in serum is shown to markedly influence protein-mediated glucose transport. Lysolipids were introduced exogenously into cell membranes by incubating erythrocytes in buffer containing varying concentrations of lysolipid (under 3.2 microM). The transport-modulating potency of the lysolipids was found to be dependent both on headgroup and hydrocarbon chain. MPL (monopalmitoyl lecithin, L-alpha-lysopalmitoylphosphatidylcholine) had the greatest influence on sugar transport. 15 min incubation of red cells in MPL suspensions sufficed for 99% association of the lysolipid with the cell membranes. This association correlated with altered red-cell sugar transport. At MPL/bilayer lipid molar ratios as low as 0.03%, MPL was found to act as a reversible, hyperbolic, mixed-type inhibitor of exchange D-glucose exit (both Km(app) and Vmax for transport are reduced). Dissociation of MPL from the membrane results in the recovery of original transport activity. MPL at 1.5.10(-17) mol MPL/red cell was found to reduce Ki(app) for D-glucose inhibition of cytochalasin B binding to the glucose carrier protein in red cell ghost membranes. Our findings demonstrate that red-cell membrane-exogenous lysolipid associations can significantly modify protein mediated sugar transport. The simplest explanation of our findings is a direct interaction of lysolipid with the transport protein.