A study of membrane potential across isolated fruit cuticles for NaCl and CaCl2 solutions

Fixed charge density and ionic diffusion ratio in an isolated tomato fruit cuticular membrane have been estimated from membrane potential measurements for NaCl and CaCl2 electrolyte solutions. The values of the parameters studied show marked differences in the electrical behaviour of the electrolytes, and evidence the asymmetric character of the cuticular membrane. While the membrane potential values for NaCl solutions can be explained in terms of a Donnan potential plus diffusion potentials, for CaCl2 solutions the membrane potential values agree very well with the diffusion potential. These facts could be explained by taking into account some structural features of the cuticular membrane.