Effects of extracellular potassium on acid release and motility initiation in Toxoplasma gondii.
The internal pH (pHi) of Toxoplasma gondii was estimated by measuring the accumulation of the weak base 9-aminoacridine in buffers with various ionic compositions. The pHi of the metabolizing parasite increased when the extracellular K+ was elevated in alkaline medium or when the external pH (pHe) was substantially increased in medium employing high external K+ (90 mM). The parasite in mouse peritoneal fluid, or in potassium sulfate buffer (pH 8.2), where the pHi was demonstrated to be increased to 7.9, became motile when acidic buffer was substituted for the original suspension medium. This acid-induced independent movement subsided within 5 min but was repeatedly induced if the pHe was serially lowered to 6.0. Basic buffers, on the other hand, abolished motility when applied to the moving parasites. Nigericin, which is known to collapse pH gradients across the membrane, also abolished motility.
Endo
T
T
Department of Parasitology, National Institute of Health, Tokyo, Japan.
Tokuda
H
H
Yagita
K
K
Koyama
T
T
D000818:Animals; D001693:Biological Transport, Active; D002465:Cell Movement / Q000187:drug effects; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D008857:Microscopy, Interference; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D014122:Toxoplasma / Q000378:metabolism* / Q000502:physiology
D003470:Culture Media; D011188:Potassium