RESUMEN
Mechanical characteristics of bilayer lipid membranes (BLM) composed of alkenylacyl-, alkylacyl-, and diacyl-glycerophosphocholines were studied by measuring modulus of elasticity in the direction normal to BLM plane, E perpendicular, and coefficient of dynamic viscosity eta. Alkenylacyl-glycerophosphocholine (choline plasmalogen) BLM typically show larger values of E perpendicular and eta as compared to their analogs, suggesting a tighter packing of their hydrophobic regions. Increasing cholesterol concentrations are associated with monotonically increasing values of parameters E perpendicular and eta of plasmalogen BLM, whereas a nonmonotonic dependence of these parameters with a maximum around c = 66 mol% cholesterol is typical for the diacyl analog POPC. This may be due to the formation of cholesterol clusters at c > 66 mol%.
Asunto(s)
Membrana Dobles de Lípidos/química , Fosfatidilcolinas , Plasmalógenos , Colesterol , Elasticidad , Cinética , Relación Estructura-Actividad , ViscosidadRESUMEN
The interactions between haematoporphyrin (HP) and bilayer lipid membranes (BLM) were studied. A weak effect of HP on BLM conductivity was observed at HP concentrations ranging between 10(-6) and 3 x 10(-5) mol/l. Modulus of elasticity in the direction normal to the membrane plane (E perpendicular) and dynamic viscosity coefficient (eta) were measured, both exhibiting HP-induced decrease by 22-31% in the dark. In this case, membrane potential Vm became negative and reached a value close to -50 mV. Under illumination by low-intensity (1 mW) He-Ne laser (lambda = 632 nm) the values of parameters E perpendicular and eta of the HP-modified membranes increased by 41-66%, and Vm decreased to -20 mV. Upon removing HP from the solution by perfusion, irreversible changes in mechanical properties of the HP-modified membranes induced by the laser light were observed. The reason could be the formation of stable complexes of HP with the lipid molecules. HP binds to membrane noncooperatively, with a binding constant K approximately 10(5) l/mol.