Studies on phosphatidylcholine model membranes. I. Iodine permeability measurement by specific ion electrode.

An iodide specific ion electrode was used to measure iodide released from egg phosphatidylcholine liposomes after passage through an ion exchange column. The permeation process was shown to be a sum of two separate first order processes. The method permits linear initial rates of iodide release to be determined for the first 5 min of permeation. Iodide permeability in the absence of Tris buffer was found to be a decreasing function of pH. In the presence of Tris, iodide permeability went through a minimum ofrom ph 7.3-8.5. the permeability was found to decrease when cholesterol was incorporated into the liposomes.