Presence Of Erythrocyte Membranes Research Articles

Effects of albumin and erythrocyte membranes on spread monolayers of lung surfactant lipids

Dipalmitoyl phosphatidylcholine (DPPC), one of the main constituents of lung surfactant is mainly responsible for reduction of surface tension to near 0 mN/m during expiration, resisting alveolar collapse. Other unsaturated phospholipids like palmitoyloleoyl phosphatidylglycerol (PG), palmitoyloleoyl phosphatidylcholine (POPC) and neutral lipids help in adsorption of lung surfactant to the air–aqueous interface. Lung surfactant lipids may interact with plasma proteins and hematological agents flooding the alveoli in diseased states. In this study, we evaluated the effects of albumin and erythrocyte membranes on spread films of DPPC alone and mixtures of DPPC with each of PG, POPC, palmitoyloleoyl phosphatidylethanolamine (PE), cholesterol (CHOL) and palmitic acid (PA) in 9:1 molar ratios. Surface tension–area isotherms were recorded using a Langmuir–Blodgett (LB) trough at 37 °C with 0.9% saline as the sub-phase. In the presence of erythrocyte membranes, DPPC and DPPC + PA monolayers reached minimum surface tensions of 7.3 ± 0.9 and 9.6 ± 1.4 mN/m, respectively. Other lipid combinations reached significantly higher minimum surface tensions >18 mN/m in presence of membranes (Newman Keul's test, p < 0.05). The relative susceptibility to membrane inhibition was [(DPPC + PG, 7:3) = (DPPC + PG, 9:1) = (DPPC + POPC) = (DPPC + PE) = (DPPC + CHOL)] > [(DPPC + PA) = (DPPC)]. The differential response was more pronounced in case of albumin with DPPC and DPPC + PA monolayers reaching minimum surface tensions less than 2.4 mN/m in presence of albumin, whereas DPPC + PG and DPPC + POPC reached minimum surface tensions of around 20 mN/m in presence of albumin. Descending order of susceptibility of the spread monolayers of lipid mixtures to albumin destabilization was as follows: [(DPPC + PG, 7:3) = (DPPC + PG, 9:1) = (DPPC + POPC)] > [(DPPC + PE) = (DPPC + CHOL)] > [(DPPC + PA) = (DPPC)] The increase in minimum surface tension in presence of albumin and erythrocyte membranes was accompanied by sudden increases in compressibility at surface tensions of 15–30 mN/m. This suggests a monolayer destabilization and could be indicative of phase transitions in the mixed lipid films due to the presence of the hydrophobic constituents of erythrocyte membranes.

Interaction of NAD-dependent dehydrogenases with human erythrocyte membranes. Evidence that D-glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase are catalytically active in a membrane-bound state.

Interaction of D-glyceraldehyde-3-phosphate dehydrogenase (GPDH) and lactate dehydrogenase with human erythrocyte membranes was studied. Under the conditions of low ionic strength, both enzymes bound to the membranes with similar affinities (kd = 1 microM). The binding was accompanied by complete inhibition of GPDH and by a 65-75% inhibition of lactate dehydrogenase (LDH). Increasing the ionic strength to physiologically meaningful values (0.15 M) completely abolished the inactivation of both dehydrogenases in the presence of erythrocyte membranes, but did not preclude their binding. These results suggest that different modes of enzyme-membrane interaction can be realized under the conditions of low and high ionic strength. They also indicate that GPDH and LDH are capable of functioning in a membrane-bound state.

The penetration of local anesthetics into the red blood cell membrane as studied by fluorescence quenching

The local anesthetics procaine and tetracaine were found to quench the fluorescence of the probes N-octadecyl naphthyl-2-amine 6-sulfonic acid and 12-(9-anthroyl)stearic acid in the presence of erythrocyte membranes. This quenching was shown to be due to the aromatic amine of the procaine and tetracaine molecules. Lidocaine, an active anesthetic that does not contain an aromatic amine in the same position as does procaine and tetracaine did not quench either of the fluorophores. The preferential quenching of the fluorescent probes by procaine and tetracaine indicated a greater accessibility of tetracaine than of procaine to the hydrocarbon region of the membrane and a greater accessibility of procaine than of tetracaine at the membrane's surface. The addition of calcium was found to reverse the quenching of 12-(9-anthroyl)stearic acid by tetracaine in the presence of red cell membranes.

The interaction of small molecules with spin-labelled erythrocyte membranes

The spectra of non-covalent spin labels have been examined in the presence of erythrocyte membranes and their separated lipid and protein components. Evidence has been obtained for the perturbations induced in the membrane structure by a range of extraneous molecules. The perturbations are detected either as changes in the spectra of the bound spin label, or as changes in the partition of the spin label into the membrane. A comparison of the perturbations detected by different spin labels provides preliminary evidence for the localisation of the perturbing agents in the membrane. With steroid spin labels it is possible to detect the onset of irreversible structural breakdown in the membrane at high concentrations of perturbing agents. This results in the exposure of new protein binding sites for the steroid spin labels which are not accessible in the intact membrane. The interpretation of the spin label experiments is supported in detail by directly comparable studies of the nuclear magnetic relaxation of the same perturbing agents in erythrocyte membranes.

Relaxation of anaesthetics in the presence of cyto-membranes.

WE recently showed that the nuclear magnetic relaxation rate of benzyl alcohol is increased in the presence of erythrocyte membranes and we concluded that this is caused by restriction of the molecular motion of the alcohol molecules imposed by the membrane structure1. With changes in alcohol concentration the relaxation rate altered in a characteristic way (Fig. 1), and it was suggested that alterations in membrane structure were induced by the alcohol which might be correlated with the physiological changes found in anaesthetic action.