Chloride removal and excitation-contraction coupling in guinea pig ileal smooth muscle.
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)
D000818:Animals; D000838:Anions; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology*; D004148:Dioxolanes / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D007513:Isethionic Acid / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology
D000838:Anions; D002712:Chlorides; D004148:Dioxolanes; D007473:Ion Channels; D005711:Gallopamil; C028858:methamilane methiodide; D007513:Isethionic Acid; D002118:Calcium