Attention is drawn to the fact that the non-linear electrical currentvoltage characteristic of porous track-etched poly(ethylene terephtalate) membranes, reported by Wolf, Siwy, Korchev and Spohr in Cell. Mol. Biol. Lett. 4 (1999) 553-565, is very similar to that observed with cross-linked polyelectrolyte gel membranes with negatively charged fixed ionic groups (cation exchange membranes). This...
