title: Biophysical characterization of a large conductance anion channel in hypodermal membranes of the gastrointestinal nematode, Ascaris suum.
abstract: 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.
authors.affiliation: Pharmacia Corporation, Mailstop 7923-25-410, Kalamazoo, MI 49007-4940, USA.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Blair
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Geary
authors.forename: Sharon K
authors.initials: SK
authors.lastname: Mensch
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Vidmar
authors.forename: S Kevin
authors.initials: SK
authors.lastname: Li
authors.forename: Norman F H
authors.initials: NF
authors.lastname: Ho
authors.forename: David P
authors.initials: DP
authors.lastname: Thompson
mesh_terms: 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
chemical_list: D000838:Anions; D007473:Ion Channels