Diffusible sodium, potassium, magnesium, calcium and phosphorus in frog skeletal muscle.

Abstract

SUMMARY1. A microvolumetric analytical method has been developed to measure the endogenous concentrations of diffusible elements in muscle cells.2. Single twitch fibres from frog muscle were skinned under oil and 0-2 nl drops of isosmotic sucrose solution, held in the tips of specially constructed pipettes, were placed in contact with the skinned fibres. After 0-10 min, the microdrops were removed and analysed with a wave-length dispersive X-ray spectrometer.3. The uptake of Na, K, Mg, and P into the microdrops was well fitted by a single exponential function, while the uptake of Ca was better represented by the sum of two exponential functions. All elements analysed except Ca reached diffusional equilibrium within 5 min of placing the microdrop on the fibre, while Ca was still not equilibrated at 10 min.4. For freshly isolated muscle fibres, diffusible element concentrations in the microdrops at equilibrium were (in mm, mean + S.D.): Na, 7-6 ± 72; K, 82 + 36; Mg, 5-8 + 30; P, 51+19. Diffusible Ca concentration (at 10 min elapsed sampling time) was 0-7+04 mM.5. Results from experiments in which microdrops were equilibrated with skinned fibres pre-soaked in an artificial (Ca-free) solution support the notion that the exogenous solutes can replace the endogenous diffusible contents of a skinned fibre by soaking the skinned fibre in a relatively large volume of the artificial solution.6. Total Na, K, Mg, Ca, and P content of whole muscle was measured by electron probe analysis of muscle extracts. In freshly isolated muscle, whole muscle element content was (in mmol/kg wet weight, mean + S.D.): Na, 21+8; K, 120+ 26; Mg, 9-7+2-6; Ca, 2-2+0-5; P, 76+ 18.

The intracellular concentration of free magnesium in extensor digitorum longus muscles of the rat

“…It is, however, in agreement with values for [Mg2+], determined in other muscle fibres (e.g. Gupta & Moore, 1980;Maughan & Recchia, 1985;Alvarez-Leefmans et al 1986;Blatter & McGuigan, 1986 …”

“…For example, [Mg2+] was estimated to be between 0-2 and 0 6 mm when based on electron probe microanalysis (Maughan & Recchia, 1985) while a value of 0-6 mm was reported (Gupta & Moore, 1980) using 31P NMR spectroscopy.…”

A quantitative analysis of cell volume and resting potential determination and regulation in excitable cells

“…E m , V c and each of the intracellular solute concentrations gradually approached stable final steady state values that strikingly reproduced the intracellular ion concentrations and E m found in frog skeletal muscle (Hodgkin & Horowicz, 1959; Maughan & Recchia, 1985) despite such arbitrary starting parameters. The membrane potential E m(MN) was also calculated at each time point using the Mullins‐Noda (MN) equation (Mullins & Noda, 1963) for comparison with the corresponding result E m(CD) from the charge difference equation.…”

“…The numerical model specifically avoided any dependence on the assumption of electrochemical equilibrium that was necessitated by earlier calculations of the membrane potential, E m , using the Goldman‐Hodgkin‐Katz (GHK) equation or its derivatives (Mullins & Noda, 1963; Armstrong, 2003). Thus E m was calculated at each iteration time point, t , from the difference between the sums of the intracellular positive and negative charges, i.e. F is Faraday's constant (C mol −1 ), C m (C V −1 l −1 ) is the membrane capacitance referred to unit cell volume, [X − ] i represents the total concentration ( m ) of a variety of osmotically active and normally membrane impermeant cellular constituents that include cytosolic proteins, amino acids, nucleotides and phosphorus‐containing anions (Maughan & Recchia, 1985; Maughan & Godt, 2001) and z X (dimensionless) is the mean charge valency of X − . z X is negative; thus [X − ] i balances the charge of the high intracellular cation concentrations.…”

“…These parameters are representative of amphibian skeletal muscle, and are derived from a variety of sources. (Adrian, 1956; Eisenberg & Gage, 1969; Gage & Eisenberg, 1969; Maughan & Recchia, 1985; Hernandez et al 1989; Huang & Peachey, 1989; Thompson & Fitts, 1992; Hernandez & Chifflet, 2000; Maughan & Godt, 2001; Clausen, 2003).…”