Significant Differences Between Procyclic and Bloodstream Forms of Trypanosoma brucei in the Maintenance of their Plasma Membrane Potential

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Abstract
The plasma membrane potential (ΔΨ) of procyclic and bloodstream trypomastigotes of Trypanosoma brucei was studied using the potentiometric fluorescent dye bisoxonol. Our results suggest that a proton pump plays a significant role in the regulation of AΨ in procyclic and bloodstream forms, as evidenced by depolarization of the plasma membrane by H+-ATPase inhibitors (e.g. dicyclohexylcarbo-diimide, N-ethylmaleimide, diethylstilbestrol, and bafilomycin A1). In bloodstream stages the plasma membrane was significantly depolarized by ouabain only when the cells were incubated in sodium-rich buffers indicating that a sodium pump was being inhibited. In contrast, ouabain had no effect on the AΨ of the procyclic stages in a sodium-rich buffer. However, it induced an additional significant depolarization in these stages when their plasma membrane was already partially depolarized by the H+-ATPase inhibitor dicyclohexylcarbo-diimide, indicating the presence of an ouabain-sensitive sodium pump whose activity is masked by the H+-ATPase. Unlike procyclic forms, the AΨ of bloodstream-stage trypomastigotes was markedly sensitive to extracellular Na+ and K+concentrations. Thus, there are significant differences between procyclic and blooodstream forms in the maintenance of the AΨ and in their permeability to cations.

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