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Effects of pH on a high conductance Ca-dependent chloride channel: a patch-clamp study in Ascaris suum

Published online by Cambridge University Press:  06 April 2009

A. P. Robertson  and
R. J. Martin
A. P. Robertson*
Affiliation:
Department of Preclinical Veterinary Sciences, R.(D.) S.V.S., Summerhall, University of Edinburgh, Edinburgh EH9 1QH
R. J. Martin
Affiliation:
Department of Preclinical Veterinary Sciences, R.(D.) S.V.S., Summerhall, University of Edinburgh, Edinburgh EH9 1QH
*
*Corresponding author. Tel: 0131 650 6094. E-mail: alanr@lab0.vet.ed.ac.uk.
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Summary

Plasma membrane vesicles prepared from the bag region of the somatic muscle cells of the parasitic nematode Ascaris suum contain high conductance, voltage sensitive, Ca-dependent chloride channels, suggested to be involved in the excretion of carboxylic acids produced by the anaerobic respiration of glucose (Valkanov, Martin & Dixon, 1994). The effect of altered pH on this channel was investigated using the patch-clamp technique and isolated inside-out membrane patches. Changes in pH had little effect on channel conductances and only a small effect on reversal potentials. Under control conditions (symmetrical pH 7·2) the channel had the highest probability of opening at ∼ — 35 mV (the resting membrane potential of the cell). At positive membrane potentials the probability of opening decreased. The Boltzmann equation was used to describe the relationship between membrane potential and probability of channel opening, and to calculate the effective gating charge. Reduction of external pH produced an increase in the probability of channel opening at hyper-polarized membrane potentials. An increase in internal pH caused a voltage-independent increase in the probability of channel opening and made the effective gating charge less negative. The effect of reducing internal pH was marked: the channel then opened most frequently at positive membrane potentials and the probability of opening at —35 mV was greatly reduced. The decrease in internal pH changed the polarity of the effective gating charge. A simple model was constructed to describe the effects of pH on channel gating.

Keywords

patch-clampAscaris suumCl− channelpHeffective gating charge
Type
Research Article
Information
Parasitology , Volume 113 , Issue 2 , August 1996 , pp. 191 - 198
Copyright
Copyright © Cambridge University Press 1996

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