title: Mechanisms for monovalent cation-dependent depletion of intracellular Mg2+:Na(+)-independent Mg2+ pathways in guinea-pig smooth muscle.
abstract: 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 beta-ATP peak alone and (2) beta- and gamma-ATP peaks. Both estimations indicated that [Mg2+]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 Mg2+ with NMDG substitution. Substituting extracellular Na+ with the small cation, Li+, also shifted the beta-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 Mg(2+)-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.
authors.affiliation: Department of Cell Physiology, Nagoya University Graduate School of Medicine, Nagoya, Japan. h44673a@nucc.cc.nagoya-u.ac.jp
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Nakayama
authors.forename: Hideki
authors.initials: H
authors.lastname: Nomura
authors.forename: Lorraine M
authors.initials: LM
authors.lastname: Smith
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Clark
authors.forename: Tadayuki
authors.initials: T
authors.lastname: Uetani
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Matsubara
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002414:Cations, Monovalent / Q000378:metabolism; D002432:Cecum / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D009129:Muscle Tonus / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D002414:Cations, Monovalent; D000255:Adenosine Triphosphate; D012964:Sodium; D008274:Magnesium; D002118:Calcium