title: Determination of the membrane potential of vacuoles isolated from red-beet storage tissue : Evidence for an electrogenic ATPase.
abstract: The membrane potential of isolated vacuoles of red beet (Beta vulgaris L.) was estimated using several methods. The quenching of the fluorescence of the cyanine dyes 3,3'-diethylthiodicarbocyanine iodide (DiS-C2-(5)) and 3,3'-dipropylthiodicarbocyanine iodide (DiS-C3-(5)) in vacuoles indicated a transmembrane potential difference, negative inside at low external potassium concentrations. The Δψ was found to be-55 mV with two other methods, the distribution of (204)T1(+) in the presence of valinomycin and the distribution of the lipophilic cation triphenylmethylphosphonium. Uncouplers reduced this value to-35 mV. High external potassium concentrations, comparable to cytosolic values, abolished the membrane potential almost completely. The addition of 1 mM Tris-Mg(2+)-ATP markedly hyperpolarized the membrane to-75 mV. This effect was prevented by inhibitors of the ATPase activity located in isolated vacuole membranes.
authors.affiliation: Botanisches Institut der Universität, Gyrhofstraße 15, D-5000, Köln 41, Federal Republic of Germany.
authors.forename: S
authors.initials: S
authors.lastname: Doll
authors.forename: R
authors.initials: R
authors.lastname: Hauer