Calcium antagonism by cobalt ions on contraction of guinea-pig taenia coli.
In guinea-pig taenia coli, cobalt ions (Co2+) inhibited the tonic response to a highly concentrated K+ solution (high-K+, 40 mM) more strongly than the phasic response. Co2+ displaced Ca2+ concentration-response curves to the right, inhibited the increase in tissue calcium content caused by high-K+, and inhibited Ca2+ binding at low affinity sites more than at high affinity sites. After treatment with Co2+, the tonic tension caused by high-K+ was not restored by a wash with normal medium, but it was restored by a wash with EDTA. The cobalt remaining in muscles was almost completely eliminated after a 20-30 min wash with EDTA. The results suggest that Co2+ binds chiefly to the surface membrane of taenia coli. Co2+ probably reduced the tension in response to high-K+ mainly by inhibiting Ca2+ influx rather than by affecting Ca2+ release.
Nasu
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Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002132:Calcium Radioisotopes; D003035:Cobalt / Q000493:pharmacokinetics / Q000494:pharmacology*; D003106:Colon / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D003035:Cobalt; D007811:Lanthanum; D000255:Adenosine Triphosphate; D011188:Potassium