Concentration dependence of permeability coefficient to an electrolyte component across bovine lens capsule in vitro.

Theoretical and experimental studies have been made on permeability coefficients to various kinds of electrolyte across lens capsules that are dissected from bovine eyes and that are found to be positively fixed charged membranes from our experiments of membrane potentials. The differential permeability coefficient, P(m), is defined as J(s) = P(m)(C(2) - C(1)), where J(s) is the flux of an electrolyte component in moles per sec across unit area of the lens capsule that separates two aqueous solutions of the same electrolyte at different concentrations, C(2) and C(1). Various types of strong electrolytes were studied; KCl, NaCl, Cacl(2), MgSO(4), MgCl(2) and LaCl(3). It was found that at C(2)/C(1) = constant, P(m) decreases to zero as C(2) decreases and P(m) increases to a limiting value, (P(m))(infinity), that is characteristic for the system of the salt used and the membrane as C(2) increases, despite of electrolytes. We assumed in theory that single ion activity coefficients of co-ion and gegen-ion are ideal, that the systems studied are in electric neutrality, that the fixed charge density of the membrane is independent of concentrations C(2), and that Donnan equilibrium holds between the bulk solution and membrane surface. Although the concentration-dependent changes of P(m) were quantitatively different depending on the type of electrolyte used, general agreement between theory and experiment was obtained over a wide range of concentrations except for the case of very dilute solutions.