Low pH promotes parasite motility and microneme secretion.

<p>(A) Videomicroscopy analysis of pH dependent parasite motility. Parasites were purified in high K⁺ buffer (pH 8.4) and analyzed before and after exchanging to the same buffer at pH 7.4 or 5.4. Graph indicates the average and standard deviation of 3 independent experiments. *<i>p</i><0.05 vs. pH 7.4 by student's <i>t</i>-test. (B) Immunoblot analysis of pH dependent microneme secretion. Parasites were purified in Endo buffer and switched to Endo buffer of the indicated pH, incubated for 2 min at 37°C and placed on ice. Blots of secreted material were probed with antibodies for MIC10, MIC4 or GRA1 as indicated. (C) Low pH induces more microneme secretion than ethanol stimulation and PLP1 is secreted and processed in a pH-dependent manner. Blots of secreted material were probed with antibodies for PLP1 and GRA4 as indicted. Also shown is a blot of PLP1 from cell pellets (cellular fraction) obtained by centrifugation after secretion. (D) Low-pH induced microneme secretion is blocked by the Ca²⁺ chelator, BAPTA-AM, as observed by immunoblot of PLP1, MIC2, MIC10, and MIC4. GRA1 secretion is not affected by BAPTA-AM. (E) Low pH induces microneme secretion in the presence of high K⁺ concentration. Arrowheads for panels B, D and E indicate products of SUB1 proteolysis.