Molecular properties of cetiedil and its interactions with erythrocyte membranes

Cetiedil, an antisickling agent and a vascular smooth muscle relaxant, is an amphiphilic molecule. The critical micelle concentration in 5 mM phosphate buffer with 150 mM NaCl is approximately 8.8 mM. The molecule, as the citrate salt, is highly acidic at millimolar concentrations. The UV absorption extinction coefficient at 233 nm, E233, is 2796 M-1 cm-1. The studies of free cetiedil concentrations in the presence of membrane ghosts show that large amounts of cetiedil associate with membrane samples. Spin label electron paramagnetic resonance experiments showed that the lipids and the proteins of erythrocyte membrane samples were both affected by the addition of cetiedil. However, the cetiedil effects on membrane components are reversible. The protein spin label results demonstrate the binding of cetiedil to the membrane with an apparent equilibrium dissociation constant of approximately 2 mM. The binding is saturable. The apparent half-saturation concentrations for the binding at physiological ionic strength and temperature are in the range of 1-3 mmoles of cetiedil per gram of membrane proteins. Our studies also indicate that binding is not affected by the removal of the spectrin and actin network from the membranes. Interaction of cetiedil with Band 3 molecules in the erythrocyte membrane is suggested. The regions near the lipid head groups in the membrane samples are also affected by cetiedil.