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.

No abstract

We have developed a nanoscale fault isolation technique based on conducting atomic force microscopy (AFM). By this technique, we located the failure points of junction leakage and gate oxide leakage with high accuracy. Furthermore, we obtained the I-V curves by direct probing to 0 . 2~ contact plugs and verified the failure model of junction leakage. This technique is useful for a nanoscale fault isolation. It has an additional advantage of being available for samples without interconnects or electrodes, so that it can be applied to physical analysis of the samples after removal of metal layers or in-line inspection during the fabrication process.