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This Article Full Text Full Text (PDF) All Versions of this Article: 551/3/843    most recent jphysiol.2003.047795v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nakayama, S. Articles by Matsubara, T. Search for Related Content PubMed PubMed Citation Articles by Nakayama, S. Articles by Matsubara, T.

MECHANISMS FOR MONOVALENT CATION-DEPENDENT DEPLETION OF INTRACELLULAR MG²⁺:NA⁺-INDEPENDENT MG²⁺ PATHWAYS IN GUINEA-PIG SMOOTH MUSCLE

Shinsuke Nakayama, Hideki Nomura, Lorraine M. Smith, Joseph F. Clark†, Tadayuki Uetani* and Tatsuaki Matsubara*

It has been suggested that magnesium deficiency is correlated with many diseases. ³¹P NMR experiments were carried out in order to investigate the effects of Na⁺ substitution on Mg²⁺ depletion in smooth muscle under divalent cation-free conditions. In the taenia of guinea-pig caeci, the intracellular free Mg²⁺ concentration ([Mg²⁺]_i) was estimated from the chemical shifts of (1) the -ATP peak alone and (2) - and -ATP peaks. Both estimations indicated that [Mg²⁺]_i decreased only very slowly in Mg²⁺-free, Ca²⁺-free solutions in which Na⁺ was substituted with large cations such as NMDG (N-methyl-D-glucamine) and choline. Furthermore, the measurements of tension development supported the suggestion of preservation of intracellular Mg²⁺ with NMDG substitution. Substituting extracellular Na⁺ with the small cation, Li⁺, also shifted the -ATP peak towards a lower frequency, but the frequency shift was significantly less than that seen upon Na⁺ substitution with K⁺. The estimated [Mg²⁺]_i depletion was, however, comparable with that seen after Na⁺ substitution with K⁺ using the titration curves of metal-free and Mg²⁺-bound ATP obtained in Li⁺-based model solutions. It was concluded that Mg²⁺ rapidly decreases only when small cations were the major electrolyte of the extracellular medium. Na⁺ substitutions with NMDG, choline or Li⁺ had little effect on intracellular ATP concentration after 100 min treatment.

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