Biophysical characterization of a large conductance anion channel in hypodermal membranes of the gastrointestinal nematode, Ascaris suum.
Patch-clamp recordings from muscle- and cuticle-facing hypodermal membranes of the gastrointestinal nematode Ascaris suum reveal a high-conductance, voltage- sensitive Ca(2+) -dependent Cl(-) channel. The hypodermal channel has a conductance of 195 pS in symmetrical 160 mM NaCl. The open probability of the channel is highly voltage-sensitive, and channel activity is not observed when Ca(2+) is reduced to <100 microM. The channel is permeable to organic anions that are major end-products of carbohydrate metabolism in A. suum, including acetate, butyrate and 2-methylvalerate. The conductances and relative permeabilities of these organic anions are inversely related to size, with 2-methylvalerate being only approximately 3% as permeable as Cl(-). The diameter of the channel pore was 12.3+/-0.2 A, calculated from the relative permeability coefficients of Cl(-) and the organic anions. Results of this study are consistent with the hypothesis that the large conductance anion channel in A. suum hypodermal membranes provides a low energy pathway for organic anion excretion from the hypodermal compartment, followed by diffusion across the aqueous channels of the cuticle matrix.
Blair
Kevin L
KL
Pharmacia Corporation, Mailstop 7923-25-410, Kalamazoo, MI 49007-4940, USA.
Geary
Timothy G
TG
Mensch
Sharon K
SK
Vidmar
Thomas J
TJ
Li
S Kevin
SK
Ho
Norman F H
NF
Thompson
David P
DP
D000818:Animals; D000838:Anions; D017165:Ascaris suum / Q000378:metabolism* / Q000502:physiology; D005260:Female; D007473:Ion Channels / Q000378:metabolism* / Q000503:physiopathology; D008564:Membrane Potentials; D008854:Microscopy, Electron; D018408:Patch-Clamp Techniques
D000838:Anions; D007473:Ion Channels