The distribution of permeant ions demonstrates the presence of at least two distinct electrical gradients in bloodstream forms of Trypanosoma brucei

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Abstract
The distribution of 86Rb+ and the radiolabelled lipophilic cation [3H]methyltriphenylphosphonium (MePh3P+) was used to investigate the membrane potentials that exist in bloodstream forms of Trypanosoma brucei. Even after correction for binding to cellular constituents, the accumulation of MePh3P+ was approximately tenfold greater than the accumulation of Rb+ under resting conditions. The addition of low concentrations of carbonylcyanide p‐trifluoromethoxyphenylhydrazone or valinomycin reduced the accumulation of MePh3P+ tenfold without perturbing the accumulation of Rb+. Although selective permeabilization of the plasma membrane abolished the accumulation of Rb+ and caused a substantial decrease in the accumulation of MePh3P+, a significant carbonylcyanide‐p‐trifluoromethoxyphenylhydrazone‐sensitive accumulation of MePh3P+ persisted under these conditions. These data were consistent with the presence of at least two distinct membrane potentials (Ψ) in bloodstream forms of T. brucei; a potential across the plasma membrane (Ψp) and an additional Ψ, generated by the electrogenic movement of H+, across the membrane of an intracellular organelle that possesses no electrical permeability to Rb+ or K+.

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