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  • Title: Chloride removal and excitation-contraction coupling in guinea pig ileal smooth muscle.
    Author: Rangachari PK, Triggle CR.
    Journal: Can J Physiol Pharmacol; 1986 Dec; 64(12):1521-7. PubMed ID: 2435392.
    Abstract:
    The effect of extracellular Cl (Cl-o) removal on contractions evoked by a selective muscarinic agonist, cis-2-methyl-4-dimethylaminomethyl 1,3-dioxolane methiodide (CD), and high K+ depolarizations in the isolated guinea pig ileal longitudinal muscle was studied. The replacement of Cl-o with impermeant anions, such as isethionate (Ise-), was found to selectively inhibit a portion of the initial phasic response to K+ and CD, leaving the secondary and sustained tonic responses unchanged. In Ca2+-free solutions, the loss of contractile responses to high K+ was faster and more pronounced in Cl--free compared with Cl--containing solutions. Furthermore, the uptake of Ca2+, as represented by 45Ca2+, from the saline solution was delayed and reduced in Ise--containing Cl-o-free solutions. Replacement of Cl-o with other impermeant anions, such as gluconate and methylsulphate, had a similar action on contractile activity as for Ise-replacement. Cl-o replacement with permeant anions, such as nitrate, however, did not significantly inhibit the phasic response and sometimes increased the tonic response to K+. These results indicate that there is a Cl-o-dependent Ca2+ pool in the guinea pig ileal longitudinal muscle and we speculate that this Cl-o-dependent Ca2+ pool is associated with membrane structures, such as calveolae, which would thus offer a degree of protection to depletion by removal of extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
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