Manganese ions induce tonic contraction after relaxation in a high-K+ medium in ileal longitudinal smooth muscle of guinea-pig.
In ileal longitudinal muscle 5 mM Mn2+ inhibited completely the K+ (60 mM)-induced tonic tension to the base line; however, the tension progressively increased to above the level of original tonic response evoked by K+ after 3 h in the presence of Mn2+. Tetrodotoxin 5 x 10(-5) M) had no influence on the tension development in the presence of Mn2+ in the high-K+ medium. Mn2+ also increased the tension in a high-K+, Ca(2+)-free medium. The Ca2+ antagonist, gallopamil (10(-6) M) inhibited the development of tension in the presence of Mn2+ in the high-K+ medium. The 45Ca uptake determined by the lanthanum method remained unchanged from control levels after 3 h of the 5 mM Mn2+ application in the high-K+ medium in spite of the development of the tension. The manganese uptake in the high-K+ medium, increased in accordance with the increase of duration of 5 mM Mn2+ application. Gallopamil inhibited manganese uptake in the high-K+ medium. These results suggest that Mn2+ firstly reduces K(+)-induced tension by inhibition of Ca2+ influx, subsequently, Mn2+ ions accumulate in the intracellular compartments through voltage-operated Ca2+ channels and may activate contractile proteins in the ileal muscle.
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan.
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Nasu
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Murase
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Shibata
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D003285:Contractile Proteins / Q000378:metabolism; D005711:Gallopamil / Q000494:pharmacology; D006168:Guinea Pigs; D007082:Ileum; D008297:Male; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D015220:Calcium Channels; D003285:Contractile Proteins; D005711:Gallopamil; D008345:Manganese; D013779:Tetrodotoxin; D011188:Potassium; D002118:Calcium