Intracellular free magnesium in frog skeletal muscle fibres measured with ion-selective micro-electrodes

J Physiol. 1986 Sep;378:461-83. doi: 10.1113/jphysiol.1986.sp016230.


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)

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • In Vitro Techniques
  • Ion Channels / physiology
  • Magnesium / pharmacology
  • Magnesium / physiology*
  • Membrane Potentials / drug effects
  • Microelectrodes
  • Muscles / physiology*
  • Potassium / physiology
  • Rana pipiens
  • Ranidae
  • Sodium / physiology


  • Ion Channels
  • Sodium
  • Magnesium
  • Potassium