title: Factors that determine the plasma-membrane potential in bloodstream forms of Trypanosoma brucei.
abstract: The plasma-membrane potential (Delta(psi)p) in bloodstream forms of Trypanosoma brucei was studied using several different radiolabelled probes: 86Rb+ and [14C]SCN- were used to report Delta(psi)p directly because they distribute in easily measured quantities across the plasma membrane only, and [3H]methyltriphenylphosphonium (MePh3P+) was used to report Delta(psi)p only when Delta(psi)m had been abolished with FCCP because it reports the algebraic sum of the two potentials when used alone. The unperturbed Delta(psi)p had a value of -82 mV and was found to be essentially identical with, and determined almost completely by, the potassium diffusion potential, as evidenced by: (a) the lack of effect of valinomycin on the value obtained under appropriate conditions when any of these probes were used; (b) the close agreement of this measured value with that predicted from the measured distribution of K+ across the plasma membrane (-76 mV); (c) the large effect of changes in the extracellular K+ concentration by substitution with Na+ on Delta(psi)p together with the complete lack of effect of substitution of extracellular Na+ by the choline cation or substitution of extracellular Cl- by the gluconate anion on Delta(psi)p. The contribution to Delta(psi)p by electrogenic pumping of Na+/K+-ATPase was found to be small (of the order of 6 mV). H+ was not found to be pumped across the plasma membrane or to contribute to Delta(psi)p.
authors.affiliation: Department of Biochemistry, Trinity College, University of Dublin, Ireland.
authors.forename: D P
authors.initials: DP
authors.lastname: Nolan
authors.forename: H P
authors.initials: HP
authors.lastname: Voorheis
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology*; D002713:Chlorine / Q000378:metabolism; D005942:Gluconates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D007477:Ions; D008564:Membrane Potentials; D009840:Oligomycins / Q000494:pharmacology; D009861:Onium Compounds / Q000493:pharmacokinetics; D011188:Potassium / Q000378:metabolism; D012414:Rubidium Radioisotopes / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013997:Time Factors; D014320:Triphenylmethyl Compounds / Q000493:pharmacokinetics; D014346:Trypanosoma brucei brucei / Q000502:physiology*; D014475:Uncoupling Agents; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D005942:Gluconates; D007476:Ionophores; D007477:Ions; D009840:Oligomycins; D009861:Onium Compounds; D012414:Rubidium Radioisotopes; D014320:Triphenylmethyl Compounds; D014475:Uncoupling Agents; C011561:triphenylmethylphosphonium; D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002713:Chlorine; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose; D005990:Glycerol; C030691:gluconic acid; D011188:Potassium