A patch-clamp study of the ionic selectivity of the large conductance,ca-activated chloride channel in muscle vesicles prepared fromAscaris suum |
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Authors: | D M Dixon M Valkanov R J Martin |
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Institution: | (1) Department of Pre-Clinical Veterinary Sciences, R.(D).S.V.S., University of Edinburgh, Edinburgh EH9 1QH;(2) Central Laboratory of Biophysics, Bulgarian Academy of Sciences, Sofia, Bulgaria |
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Abstract: | Summary Plasma membrane vesicles prepared from the bag re gion of the somatic muscle cell of the parasiteAscaris suum contain a large conductance, voltage-sensitive, calcium-activated chloride channel. The ability of this channel to conduct
a variety of anions has been investigated using the patch-clamp technique on isolated inside-out patches of muscle membrane.
Symmetrical Cl solutions (140 mm) produced single-channel I/V plots with reversal potentials of 0 mV, substitution of bath
Cl by 140 mM NO3, Br and I caused depolarizing shifts in the reversal potentials. Replacement of the internal Cl by F (140 mM) caused a large
hyperpolarizing shift in the reversal potential. The channel dis played a permeability sequence of I > Br = NO3> Cl > F which differed from the corresponding conductance sequence Cl > NO3 = Br = I > F. The ionic environment within the channel pore has been investigated using Reuter and Stevens (1980) plots to
describe the selectivity and “fluidity” of the channel pore. In addition, the approach of Wright and Diamond (1977) was employed
to estimate the number of cationic binding sites within the channel pore. The channel is relatively fluid but the number of
cationic binding sites varies inversely with the ionic radius of the anion from 2.15 for F to 0.89 for the large planar anion
NO3 |
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Keywords: | Ascaris suum chloride channels calcium anion channel ionic permeability |
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