Mechanisms of Microenvironmental pH Regulation of the Cuticle and Implications for Transcuticular Transport in Ascaris Suum
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Authors
Magas, Louis T.
Issue Date
1990
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
The cuticle and gut of gastrointestinal nematodes are the major
interfaces between the parasite and its host animal. Previous in
vitro studies by Ho et al. (1990) have shown. that model solutes are
transported across the cuticle of Ascaris suum depending on their
molecular size, charge, pKa, and intrinsic lipid-water partition
coefficient. Recent work with whole A. suum has indicated that the
pH of the cuticle may be different from that of the bathing medium.
Therefore, in this study, the presence of a microenvironmental pH in
the cuticle of live, intact A. suum was probed using closed and open
perfusion systems. The effects of microenvironmental pH on
parasite absorption of p-nitrophenol were examined, and the
compounds responsible for the pH change were identified. The
results demonstrate that A. suum excretes the volatile fatty acids
acetate, butyrate, 2-methylbutyrate, valerate, and 2-methylvalerate.
These organic anions (pKa approximately 4.8 for each) are excreted
through the cuticle, and cause the pH of the medium in the vicinity
of the cuticle to change until reaching the pKa of these acids. The pH
change was insensitive to N2/C02 atmosphere, initial buffer pH, oral
and anal ligation, and the presence of the Na+/H+ exchange inhibitor,
amiloride. The uptake of p-nitrophenol (pKa 7.2) by A. suum was
unaffected by the initial buffer pH, ionic strength, and pH changes
during the course of 24 hour incubation. These results suggest that
the amount of weak acid or weak base drug available for absorption
will be a function of the microenvironmental pH of the cuticle rather
than the pH of the gastrointestinal tract of the host animal.
Description
vii, 79 p.
Citation
Publisher
Kalamazoo College
License
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