Abstract

In a 123 mM Li⁺ medium where all the external Na⁺ had been replaced by Li⁺, 60 mM K⁺ did not elicit any tonic contraction in the presence of 2.5 mM Ca²⁺ in taenia coli of a guinea pig. However, we found that 5 mM Mn²⁺ could induce a significant increase in tonic contraction in the 123 mM Li⁺ medium (+ 60 mM K⁺). In the absence of Ca²⁺, 5 mM Mn²⁺ could also induce a tension development in 123 mM Li+ medium (+ 60 mM K⁺). The tension by Mn²⁺ in 123 mM Li⁺ medium (+ 60 mM K⁺, Ca²⁺-free) was small. However, in Na⁺- and Ca²⁺-deficient surrounding, as external Li⁺ concentration decreased to 105 mM and 90 mM, the tension development induced by 5 mM Mn²⁺ became progressively greater. It is probable that a higher concentration of Li⁺ has greater inhibitory actions on cytosolic contractile apparatus. Phlorizin, a blocker of Na⁺-coupled glucose cotransporter, did not affect the contractions induced by 5 mM Mn²⁺ in 90, 105 or 123 mM Li⁺ medium (Ca²⁺-free, + 60 mM K⁺) in taenia coli. Presumably, this indicates that Na⁺/glucose cotransporter does not participate during contractions induced by 5 mM Mn²⁺ in Na⁺-deficient, Li⁺ medium. It is, therefore, possible that Li⁺ can not substitute for Na⁺ during the contraction due to Mn²⁺ in Na⁺-free medium.

Author Details

Authors

• T. Nasu
• M. Ooshima

Departments

• Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Yamaguchi, Japan

Address

Prof. T. Nasu
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753, Japan
Email: [email protected]

Citation