Premium
Effects of ouabain on contractions induced by manganese ions in Ca 2+ ‐free, isotonic solutions with varying concentrations of K + in guinea‐pig taenia coli
Author(s) -
Nasu Tetsuyuki,
Takahashi Katsunori
Publication year - 2005
Publication title -
fundamental and clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.655
H-Index - 73
eISSN - 1472-8206
pISSN - 0767-3981
DOI - 10.1111/j.1472-8206.2005.00334.x
Subject(s) - ouabain , taenia coli , chemistry , contraction (grammar) , sodium , biophysics , isotonic , ion transporter , guinea pig , manganese , calcium , biochemistry , membrane , medicine , endocrinology , biology , organic chemistry
The action of ouabain, a cell membrane Na + , K + ‐ATPase blocker, on contractions induced by manganese ions (Mn 2+ ) in Ca 2+ ‐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 Mn 2+ ‐induced contractions in isolated taenia coli of the guinea‐pig. Mn 2+ at 5 m m induced greater contractions as external isotonic K + concentrations progressively increased from 10 to 100 m m . Ouabain (2 × 10 −4 m ) completely inhibited tension development stimulated by 5 m m Mn 2+ in isotonic, 30 m m K + (96 m m Na + ) medium. Whereas, the tension inhibitory effects of ouabain became progressively weaker as isotonic, external K + concentrations increased to 60 m m , which successively decreased external Na + concentrations. Eventually, ouabain failed to affect contractions stimulated by Mn 2+ in isotonic, 126 m m 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 m m K + , Na + ‐sufficient (96 m m ) medium containing 5 m m Mn 2+ . These results suggested that Mn 2+ 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 Mn 2+ as the decrease in the Na + gradient across the cell membranes continues.