title: Role of diffusion potential on the flow of angiotensin II, bradykinin and related molecules through cellophane membranes.
abstract: The diffusion of electrically charged peptides (angiotensin II, bradykinin and [Suc1]angiotensin II) across tight cellophane membranes, obtained by different degrees of acetylation, shows a kinetic behaviour which was interpreted in the literature as indicative of the existence of different molecular conformations presenting slow interconversion velocities and different permeabilities across the membrane. A diffusion potential (delta psi) was found to be present across the membrane along diffusion experiments performed in low ionic strength. Upon annihilation of delta psi by chemical voltage clamping (by equally increasing the ionic strength on both bathing solutions) the diffusion rate was decreased and the flow followed first order kinetics, indicating a major role of delta psi in the process. As the ionic strength increase could also affect molecular conformation, the role of delta psi on the diffusion of those molecules was tested by fitting flux and delta psi experimental results by an integrated form of Nernst-Planck flux equation. It is concluded that the deviation from first order diffusion kinetics, observed in low ionic strength, is solely due to the diffusion potential, and not to the existence of more than one molecular conformation in aqueous solution. This study was extended to amino acids and other related charged molecules.
mesh_terms: D000804:Angiotensin II; D001920:Bradykinin; D002476:Cellophane; D004058:Diffusion; D007700:Kinetics; D008567:Membranes, Artificial; D010455:Peptides
chemical_list: D008567:Membranes, Artificial; D010455:Peptides; D000804:Angiotensin II; D002476:Cellophane; D001920:Bradykinin