Effects of High Pressure on Membrane Ion Binding and Transport

Effects of hydrostatic pressures, ranging from 1 to 1000 atmospheres, on the transport and ion binding characteristics of human red cells were studied. A high pressure stopped-flow device was designed for rapid mixing and subsequent spectrophotometric study was designed and built with the following characteristics: operating pressures up to 1200 bar, minimum average flow velocities to 2.0m/sec, dead time ranging from 5 to 25 msec. Experimental results with red cells showed that (1) normal potassium ion leakage increases dramatically at pressure 6000 psi, (2) butanol induced potassium ion leakage decreases dramatically at pressures 6000 psi, (3) the Gardos response (potassium ion leakage induced by A23187 + potassium ion) is reduced by pressure, and divalent cation selectivity sequences (Ca Mg Ba Sr) do not change with 1000 atm pressure indicating that ionic radii are of predominant importance in binding, (4) loose potassium ion binding are measured by chlorotetracycline does not change with pressure, (5) both val + potassium ion and butanol diffusion in red cell membranes have apparent activation volumes of 40 ml/mol in agreement with data on liposomes, and (6) perturbations in osmotic water flow through red cells by either high pressures or deuterium oxide substitution can be predicted from the bulk properties of pure water.