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.
Naderi
S
S
Department of Biochemistry, University of Massachusetts Medical School, Worcester 01655.
Carruthers
A
A
Melchior
D L
DL
D001786:Blood Glucose / Q000378:metabolism*; D003571:Cytochalasin B / Q000097:blood; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008051:Lipid Bilayers; D008244:Lysophosphatidylcholines / Q000097:blood / Q000494:pharmacology*; D008246:Lysophospholipids / Q000494:pharmacology*; D008627:Mercuric Chloride / Q000494:pharmacology; D011485:Protein Binding
D001786:Blood Glucose; D008051:Lipid Bilayers; D008244:Lysophosphatidylcholines; D008246:Lysophospholipids; C006065:We 201; D003571:Cytochalasin B; D008627:Mercuric Chloride