title: The membrane potential of the intraerythrocytic malaria parasite Plasmodium falciparum.
abstract: The membrane potential (Deltapsi) of the mature asexual form of the human malaria parasite, Plasmodium falciparum, isolated from its host erythrocyte using a saponin permeabilization technique, was investigated using both the radiolabeled Deltapsi indicator tetraphenylphosphonium ([(3)H]TPP(+)) and the fluorescent Deltapsi indicator DiBAC(4)(3) (bis-oxonol). For isolated parasites suspended in a high Na(+), low K(+) solution, Deltapsi was estimated from the measured distribution of [(3)H]TPP(+) to be -95 +/- 2 mV. Deltapsi was reduced by the specific V-type H(+) pump inhibitor bafilomycin A(1), by the H(+) ionophore CCCP, and by glucose deprivation. Acidification of the parasite cytosol (induced by the addition of lactate) resulted in a transient hyperpolarization, whereas a cytosolic alkalinization (induced by the addition of NH(4)(+)) resulted in a transient depolarization. A decrease in the extracellular pH resulted in a membrane depolarization, whereas an increase in the extracellular pH resulted in a membrane hyperpolarization. The parasite plasma membrane depolarized in response to an increase in the extracellular K(+) concentration and hyperpolarized in response to a decrease in the extracellular K(+) concentration and to the addition of the K(+) channel blockers Ba(2+) or Cs(+) to the suspending medium. The data are consistent with Deltapsi of the intraerythrocytic P. falciparum trophozoite being due to the electrogenic extrusion of H(+) via the V-type H(+) pump at the parasite surface. The current associated with the efflux of H(+) is countered, in part, by the influx of K(+) via Ba(2+)- and Cs(+)-sensitive K(+) channels in the parasite plasma membrane.
authors: School of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors: Richard J W
authors: RJ
authors: Allen
authors: Kiaran
authors: K
authors: Kirk
mesh_terms: D000818:Animals; D001463:Barbiturates / Q000737:chemistry; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004912:Erythrocytes / Q000469:parasitology; D005456:Fluorescent Dyes / Q000737:chemistry; D005947:Glucose / Q000378:metabolism; D007476:Ionophores; D007555:Isoxazoles / Q000737:chemistry; D018942:Macrolides / Q000494:pharmacology; D008564:Membrane Potentials; D009861:Onium Compounds / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry; D010963:Plasmodium falciparum / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects
chemical_list: D001463:Barbiturates; D005456:Fluorescent Dyes; D007476:Ionophores; D007555:Isoxazoles; D018942:Macrolides; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D015221:Potassium Channels; C052795:bis(1,3-dibutylbarbiturate)trimethine oxonol; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C040929:bafilomycin A1; D005947:Glucose; C013289:tetraphenylphosphonium