Effects of ouabain on contractions induced by manganese ions in C2+a-free, isotonic solutions with varying concentrations of K+ in guinea-pig taenia coli.
The action of ouabain, a cell membrane Na+, K+-ATPase blocker, on contractions induced by manganese ions (Mn2+) in Ca2+-free, isotonic solutions with varying concentrations of K+ in the external medium were investigated in order to evaluate the underlying role of external Na+ in Mn2+-induced contractions in isolated taenia coli of the guinea-pig. Mn2+ at 5 mM induced greater contractions as external isotonic K+ concentrations progressively increased from 10 to 100 mM. Ouabain (2 x 10(-4) M) completely inhibited tension development stimulated by 5 mM Mn2+ in isotonic, 30 mM K+ (96 mM Na+) medium. Whereas, the tension inhibitory effects of ouabain became progressively weaker as isotonic, external K+ concentrations increased to 60 mM, which successively decreased external Na+ concentrations. Eventually, ouabain failed to affect contractions stimulated by Mn2+ in isotonic, 126 mM K+, Na+-deficient medium. Ouabain caused progressively greater increase in cellular Na+ concentrations as the Na+ concentrations increased in the isotonic, K+ medium. While, pyruvate, which penetrates cell independently of external Na+, reversed the inhibition of tension by ouabain in isotonic, 30 mM K+, Na+-sufficient (96 mM) medium containing 5 mM Mn2+. These results suggested that Mn2+ induced the contraction, which was maintained by glucose transport depending on external Na+, in the case of Na+-sufficient medium in K+-depolarized taenia coli. However, it induced the contraction independent of external Na+, in the case of Na+-deficient, K+ medium. Ouabain might exhibit greater inhibition of the contraction induced by Mn2+ as the decrease in the Na+ gradient across the cell membranes continues.
Nasu
Tetsuyuki
T
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753, Japan. nasu@yamaguchi-u.ac.jp
Takahashi
Katsunori
K
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003106:Colon / Q000187:drug effects*; D004563:Electrochemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007552:Isotonic Solutions; D008297:Male; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D019289:Pyruvic Acid / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007552:Isotonic Solutions; D008345:Manganese; D010042:Ouabain; D019289:Pyruvic Acid; D000254:Sodium-Potassium-Exchanging ATPase; D009543:Nifedipine; D011188:Potassium; D002118:Calcium