Inhibition of erythrocyte phosphate transport by high pressures

Mild pressure induces resistance of erythrocytes to hemolysis by snake venom phospholipase A2

It is generally assumed that mild pressure of a few atmospheres, such as that applied to blood cells during routine centrifugation, does not affect cell function. The results of the present study refute this notion. To explore the effect of mild pressure on cell function we examined its effect on the susceptibility of red blood cells (RBC) to hemolysis by snake venom phospholipase A2 (PLA2). Rat RBC were subjected to pressure of up to five atmospheres, returned to ambient pressure and interacted with PLA2 to induce hemolysis. The hemolysis was markedly decreased with increasing the pressure applied before induction of hemolysis. Application of such a pressure induces the shedding of a chemical factor, as yet uncharacterized, which facilitates the action of PLA2 on RBC.

Electro-mechanical properties of human erythrocyte membranes: the pressure-dependence of potassium permeability

Electrical breakdown of cell membranes is interpreted in terms of an electro-mechanical model. It postulates for certain finite membrane areas that the actual membrane thickness depends on the voltage across the membrane and the applied pressure. The magnitude of the membrane compression depends both on the dielectric constant and the compressive, elastic modulus transverse to the membrane plane. The theory predicts the existence of a critical absolute hydrostatic pressure at which the intrinsic membrane potential is sufficiently high to induce "mechanical" breakdown of the membrane. The theoretically expected value for the critical pressure depends on the assumption made both for the pressure-dependence of the elastic modulus of the membrane and of the intrinsic membrane potential. It is shown that the critical pressure is expected at about 65 M Pa. The prediction of a critical pressure could be verified by subjecting human erythrocytes to high pressures (up to 100 M Pa) in a hyperbaric chamber. The net potassium efflux in dependence on pressure was used as an criterion for breakdown. Whereas the potassium net efflux was linearly dependent on pressure up to 60 M Pa, a significant increase in potassium permeability was observed towards higher pressure in agreement with the theory. The increase in the net potassium efflux above 60 M Pa was reversible, as indicated by measurements in which the same erythrocyte sample was subjected to several consecutive pressure pulses. Temperature changes in the erythrocyte suspension during compression and decompression were so small (less than 2 degrees C) that they could not account for the observed effects.

Pressure-induced variations of K+-permeability as related to a possible reversible electrical breakdown in human erythrocytes

Above a hydrostatic pressure of about 600 b a pronounced reversible increase in the net K+-efflux from human erythrocytes is observed. The effect is explained in terms of an electro-mechanical compression of the membrane, resulting in a reversible breakdown of the membrane.

Heat activation of Phycomyces blakesleeanus spores: theromdynamics and effect of alcohols, furfural, and high pressure

The thermodynamic parameters for the heat activation of the sporangiospores of Phycomyces blakesleeanus were determined. For the apparent activation enthalpy (DeltaH(#)) a value of 1,151 kJ/mol was found, whereas a value of 3,644 J./ degrees K.mol was calculated for the apparent activation entropy (DeltaS(#)). n-Alcohols (from methanol to octanol), phenethyl alcohol, and furfural lowered the activation temperature of P. blakesleeanus spores. The heat resistance of the spores was lowered concomitantly. The effect of the alcohols was a linear function of the concentration in the range that could be applied. When the log of the concentration needed to produce an equal shift of the activation temperature was plotted for each alochol against the log of the octanol/water partition coefficient, a straight line was obtained. The free energy of adsorption of the n-alcohols to their active sites was calculated to be -2,487 J/mol of CH(2) groups. Although still inconclusive, this points toward an involvement of protein in the activation process. The effect of phenethyl alcohol was similar to the effect of n-alcohols, but furfural produced a greater shift than would be expected from the value of its partition coefficient. When the heat activation of the spores was performed under high pressure, the activation temperature was raised by 2 to 4 degrees K/1,000 atm. However, with pressures higher than 1,000 atm (1.013 x 10(5) kPa) the activation temperature was lowered until the pressure became lethal (more than 2,500 atm). It is known that membrane phase transition temperatures are shifted upward by about 20 degrees K/1,000 atm and that protein conformational changes are shifted upward by 2 to 6 degrees K/1,000 atm. Consequently, heat activation of fungal spores seems to be triggered by a protein conformational change and not by a membrane phase transition. Activation volumes of -54.1 cm(3)/mol at 38 degrees C and -79.3 cm(2)/mol at 40 degrees C were found for the lowering effect of high pressure on the heat activation temperature.