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Intracellular free magnesium in frog skeletal muscle fibres measured with ion‐selective micro‐electrodes.
Author(s) -
Alvarez-Leefmans F J,
Gamiño S M,
Giraldez F,
González-Serratos H
Publication year - 1986
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 - 10.1113/jphysiol.1986.sp016230
Subject(s) - electrode , chemistry , magnesium , skeletal muscle , ion , analytical chemistry (journal) , intracellular , biophysics , materials science , anatomy , chromatography , biochemistry , biology , organic chemistry
Intracellular free Mg2+ concentration [( Mg2+]i) was measured in frog skeletal muscle fibres, using Mg2+‐selective micro‐electrodes based on the neutral ligand ETH‐1117. In calibration solutions the electrodes showed significant interference from K+, and to a lesser extent from Na+, at concentrations found intracellularly. Therefore, in order to calibrate the electrodes properly, it was necessary first to obtain an accurate value for intracellular free Na+ and K+ concentrations ([Na+]i and [K+]i), using the appropriate liquid ion exchanger micro‐electrodes. In fibres from muscles maintained in Ringer solution, the mean value for [Na+]i was 6.2 +/‐ 0.4 mM (S.E. of mean; n = 20 fibres in five muscles), while [K+]i was 104 +/‐ 1.7 mM (range 83‐122 mM; n = 25 fibres in eight muscles). Due to the substantial variability found for [K+]i, not only between fibres from different muscles, but also between fibres belonging to the same muscle, it was necessary to measure [Mg2+]i and [K+]i simultaneously in the same fibre to determine as accurately as possible the degree of K+ interference on Mg2+‐selective micro‐electrode response. In nineteen fibres from six muscles maintained in Ringer solution, the mean [K+]i was 91.7 +/‐ 2.7 mM (range 71‐110 mM), while the mean [Mg2+]i was 0.80 +/‐ 0.07 mM (range 0.2‐1.2 mM). The mean resting potential was ‐79.3 +/‐ 0.4 mV (S.E. of mean). In fifteen fibres from four muscles equilibrated in Ringer solution containing 0.5 mM‐Mg2+, the mean [K+]i was 115.5 +/‐ 0.1 mM (range 97‐129 mM) and the mean [Mg2+]i measured simultaneously in the same fibres was 1.69 +/‐ 0.21 mM (range 0.2‐2.7 mM). The mean resting potential was ‐83 +/‐ 0.7 mV. The mean [K+]i and [Mg2+]i found in these fibres was significantly higher (P less than 0.0001) than those measured in fibres from muscles maintained in standard Ringer solution (i.e. without external Mg2+). Possible explanations for this finding are discussed. Whether in the presence (0.5 mM) or in the absence of external Mg2+, our values for [Mg2+]i are distinctly lower than those previously reported by others, using the same type of Mg2+‐selective micro‐electrodes but calibrated simply from assumptions about the actual level of K+ and Na+ interference on Mg2+‐selective micro‐electrode response.(ABSTRACT TRUNCATED AT 400 WORDS)