Measurement of Transmembrane Potentials in Phospholipid Vesicles
Abstract
Phosphatidylcholine vesicles are permeable to tempotartrate, a spin-label derivative of tartaric acid. The inside-outside distribution of tempotartrate is coupled to the inside-outside distribution of H+, so it must be a measure of the transmembrane electrical potential difference in vesicles permeable to H+. This prediction is borne out by the finding that the inside-outside distribution of tempotartrate is the reciprocal of the inside-outside distribution of K+ in vesicles prepared in the presence of valinomycin.
The inside-outside distribution of tempotartrate is, by contrast, equal to the inside-outside distribution of Cl- in vesicles without valinomycin. This is evidence that an inside-outside Cl- concentration gradient induces an H+ gradient, which must be due to HCl permeation.
