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Maintenance of internal pH and an electrochemical gradient in Trypanosoma brucei
1Department of Pharmaceutical Chemistry, University of California, San Francisco 94143.
Abstract:
The internal pH value (pHi) of the long-slender bloodstream form of Trypanosoma brucei was estimated from the distribution of 14C-labeled 5,5-dimethyl-2,4-oxazolidinedione or 14C-labeled methyl amine between the intracellular space of the cells and the medium. The pHi of T. brucei remained relatively constant at 7.0-7.2 throughout an extracellular pH (pHo) range of 6.0-8.0. The maintenance of an internal pH more acidic than the environment appears to be a unique feature. Preincubation of T. brucei with carbonyl cyanide m-chlorophenyl hydrazone (CCCP) or CCCP + valinomycin had no appreciable effect on the delta pH across the T. brucei membrane when the external pH was 8.0. However, when the external pH was 6.0, CCCP abolished the observed delta pH. Nigericin significantly dissipated the delta pH across the T. brucei membrane at all pHo values. These data suggest that under physiological conditions, the maintenance of a delta pH across the bloodstream-form T. brucei membrane may be by a mechanism other than an energy-dependent gradient, whereas an energy-dependent pump may be needed for maintaining the pHi in an acidic environment. The electrical potential (delta psi) across the trypanosomal plasma membrane was also estimated using the lipophilic cation, [3H]tetraphenyl-phosphonium bromide. It appears dependent on both the external pH and the external salt conditions. Under ionic conditions similar to the host bloodstream, it ranges from -76 to -160 mV over an external pH range of 6.0 to 8.0, with an estimated value of -155.5 +/- 0.7 at the physiological pH.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
The internal pH of Trypanosoma brucei bloodstream forms stays stable around 7.0-7.2, even when the external pH changes. This study investigates the pH regulation mechanisms in this parasite.
Area of Science:
- * Parasitology
- * Cell Physiology
- * Biochemistry
Background:
- * Trypanosoma brucei causes African trypanosomiasis.
- * Understanding parasite pH regulation is crucial for drug development.
- * The bloodstream form's unique physiology requires investigation.
Purpose of the Study:
- * To estimate the internal pH (pHi) of Trypanosoma brucei bloodstream forms.
- * To investigate the mechanisms of pH homeostasis across the cell membrane.
- * To determine the electrical potential (delta psi) across the trypanosomal plasma membrane.
Main Methods:
- * Estimating pHi using radiolabeled weak acids (5,5-dimethyl-2,4-oxazolidinedione, methyl amine).
- * Assessing delta pH using ionophores (carbonyl cyanide m-chlorophenyl hydrazone, nigericin, valinomycin).
- * Measuring membrane potential (delta psi) with a lipophilic cation ([3H]tetraphenyl-phosphonium bromide).
Main Results:
- * T. brucei pHi remained stable at 7.0-7.2 across extracellular pH (pHo) 6.0-8.0.
- * A delta pH gradient was abolished by CCCP at pHo 6.0 but not at pHo 8.0.
- * Nigericin dissipated delta pH, suggesting non-energy-dependent mechanisms at physiological pH.
- * Membrane potential (delta psi) varied with pHo and salt conditions, averaging -155.5 mV at physiological pH.
Conclusions:
- * T. brucei maintains a stable internal pH, a unique feature.
- * Delta pH maintenance may involve non-energy-dependent mechanisms.
- * An energy-dependent pump might be essential for acidic pHi maintenance.
- * The trypanosomal membrane potential is sensitive to external conditions.