Solute Flux Coupling in a Homopore Membrane

Our previous studies on solute drag on frog skin and synthetic heteropore membranes have been extended to a synthetic homopore membrane. The 150-A radius pores of this membrane are formed by irradiation and etching of polycarbonate films. The membrane is 6-microm thick and it has 6 x 10(8) pores cm(-2). In this study, sucrose has been used as the driver solute with bulk flow blocked by hydrostatic pressure. As before on heteroporous membranes, the transmembrane asymmetry of tracer solute is dependent on the concentration of the driver solute. Tracer sucrose shows no solute drag while maltotriose shows appreciable solute drag at 1.5 M sucrose. With tracer inulin and dextran, solute drag is detectable at 0.5 M sucrose. These results are in keeping with the previous findings on heteropore membranes. Transmembrane solute drag is the result of kinetic and frictional interaction of the driver and tracer solutes as the driver flows down its concentration gradient. The magnitude of the tracer flux asymmetry is also dependent on the size of the transmembrane pores.