An electrical method of measuring non-electrolyte permeability

A rapid procedure based on that of Smyth & Wright (1966) is described for obtaining a measure of the permeability of rabbit gall-bladder epithelium to non-electrolytes. The underlying principles are that concentration gradients of permeant molecules produce lower rates of osmotic flow across a membrane than does the same gradient of an impermeant molecule, and that streaming potentials in the gall-bladder are directly proportional to the flow rate. Hence reflexion coefficients (cr’s) were calculated as the ratio of the streaming potential produced by a 0* 1 m gradient of the test solute to the streaming potential produced by a 0T m gradient of an impermeant reference solute, sucrose. The method yields results in agreement with those obtained in the gall-bladder by a zero-flow procedure. In general, the patterns of permeation derived are similar to those obtained in other tissues by the same procedure, by other osmotic procedures, or by direct chemical or tracer methods. The advantages of the method are that (a) large numbers of cr’s can be determined in one experiment with an average standard deviation of ± 8 % ; and (b) the minimum elapsed time between the preparation of a solution and the determination of or is about 90 s, so that cr’s may be obtained for some non-electrolytes subject to gradual chemical transformation in aqueous solution, such as aldehydes. The principles underlying osmotic methods of measuring permeability, and the effects of unstirred layers, are discussed.