Patch-clamp recordings from muscle- and cuticle-facing hypodermal membranes of the gastrointestinal nematode Ascaris suum reveal a high-conductance, voltage-sensitive Ca2+-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 Ca2+ is reduced to <100 mu M. 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 angstrom, 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. (C) 2003 Elsevier Science Inc. All rights reserved.
