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Mechanisms for monovalent cation‐dependent depletion of intracellular Mg 2+ :Na + ‐independent Mg 2+ pathways in guinea‐pig smooth muscle
Author(s) -
Nakayama Shinsuke,
Nomura Hideki,
Smith Lorraine M.,
Clark Joseph F.,
Uetani Tadayuki,
Matsubara Tatsuaki
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2003.00843.x
Subject(s) - chemistry , divalent , extracellular , magnesium , intracellular , choline , electrolyte , inorganic chemistry , crystallography , medicinal chemistry , biophysics , stereochemistry , biochemistry , organic chemistry , electrode , biology
It has been suggested that magnesium deficiency is correlated with many diseases. 31 P NMR experiments were carried out in order to investigate the effects of Na + substitution on Mg 2+ depletion in smooth muscle under divalent cation‐free conditions. In the taenia of guinea‐pig caeci, the intracellular free Mg 2+ concentration ([Mg 2+ ] i ) was estimated from the chemical shifts of (1) the β‐ATP peak alone and (2) β‐ and γ‐ATP peaks. Both estimations indicated that [Mg 2+ ] i decreased only very slowly in Mg 2+ ‐free, Ca 2+ ‐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 Mg 2+ with NMDG substitution. Substituting extracellular Na + with the small cation, Li + , also shifted the β‐ATP peak towards a lower frequency, but the frequency shift was significantly less than that seen upon Na + substitution with K + . The estimated [Mg 2+ ] i depletion was, however, comparable with that seen after Na + substitution with K + using the titration curves of metal‐free and Mg 2+ ‐bound ATP obtained in Li + ‐based model solutions. It was concluded that Mg 2+ 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.