Magnesium, Potassium, and Sodium in "Red" and "White" Muscle in the Rat

Abstract

Skeletal muscles may be classified as "red" (dark) and "white" (pale) depending on their gross color. The difference in color is due largely to the content of myoglobin in the muscle fibers. Mammalian muscles contain varying mixtures of dark and pale fibers and, therefore, are best described as "predominantly red" or "predominantly white." In the rat, the soleus is a good example of the former type of muscle; the superficial portion of the medial head of the gastrocnemius is an example of the latter tY Pe.Red and white fibers are morphologically and chemically dissimilar ( 1-3). The chemical dissimilarities include differences in the concentrations of potassium ( K ) and sodium ( N a ) ; predominantly white muscle contains more I ( and less N a than red (4, 5 ) .Potassium and also magnesium (Mg) are the most abundant intracellular inorganic cations in the soft tissues. The studies reported herein were undertaken to determine whether the distribution of Mg parallels that of K in the soleus and superficial portions of the gastrocnemius in the rat.Materials and Methods. Two groups of male albino rats (Sprague-Dawley strain) (weights of younger rats, 100-120 g, and of older rats, 250-300 g ) were used. The animals were anesthetized with ether and then exsanguinated by means of aortic puncture. The soleus, trimmed of all visible tendinous tissue, and a n equivalent amount of the medial head of the gastrocnemius were excised from each leg within 10 min of the animal's death. When measured, the total water content and extractable solids were determined by drying the muscles to constant weight at 110" for 24 hr and then perform-ing chloroform-methanol ( 2 : l ? vol/vol) extractions in Soxhlet apparatuses for 24 hr, using borosilicate thimbles. Both gastrocnemius muscles from one young animal were combined in one thimble and the soleus muscles in another. The soleus and gastrocnemius taken from one leg of an older rat were sufficient for both the water content and extractable solid determinations. Extracted and unextracted samples were transferred quantitatively to 5 .O-ml volumetric flasks. To each flask, 2 ml of concentrated HNO3 (reagent grade) was added, and the tissues were digested at 80 to 85". After dilution to 5.0 ml with distilled-deionized water, the digests were stored in polyethylene tubes until analyzed.Magnesium was determined by atomic absorption spectrophotometry ; N a and K were determined by flame photometry (6). Appropriate quantities of HN03 were added to all standards and blanks. Recoveries of known amounts of Mg and K added to the digestion mixtures were 100.4 t 1.870 and 99.3 2 0.4%, respectively; this indicated that there was no interfering effect from matrix.Unextracted muscles from one group of young rats served as controls for extracted muscles taken at the same time from a second group. The soleus and gastrocnemius from one leg of a large rat were used as unextracted controls for muscles excised from the other leg.For analysis of the significance of differences in the results, either a two-tai...

Ionic currents in slow twitch skeletal muscle in the rat.

“…This value should be compared with the value of 23 mm proposed by Kernan & MacDermott (1976). This result is consistent with the general finding that the internal sodium concentration is higher in slow than in fast fibres (Sreter & Woo, 1963;Yonemura, 1967;Chutkow, 1973). Fig.…”

Accumulation of Contaminants by Wild Turkeys and Potential for Consumer Exposure

“…When consumed, Cs 137 acts as an analog to potassium, allowing it to accumulate in muscle and other soft tissues of animals, which then act as a vector of exposure to predators and human consumers of meat (Paller et al 2014). Potassium has been found to accumulate in higher concentrations in “red” (e.g., leg) muscle compared with “white” (e.g., breast) muscle (Chutkow 1973), indicating that Cs 137 activity levels may also vary among muscle types in birds. However, the relationship between leg and breast muscle Cs 137 activity levels is largely unknown for wild gamebirds.…”