Edward Muntwyler

Amino acid content of muscle and plasma with altered pH.

The free amino acid contents of plasma and skeletal muscle were determined in rats with K + -deficiency, acute respiratory acidosis or acute respiratory alkalosis. K + -deficiency caused a reduction in intracellular pH (pH i ) and an elevation of extracellular pH (pH e ). The acute respiratory acidosis reduced skeletal muscle pH 1 to the same extent K + -deficiency did; the respiratory alkalosis imposed elevated pH e to a level comparable with K + -deficiency. This made it possible to determine whether or not altered pH 1 or pH e might directly influence the movement of amino acids into (or out of) skeletal muscle cells. Low-K + muscle contained increased amounts of basic amino acids, primarily lysine. These increases accounted for about 30 per cent of the alkali metal cation deficit found in K + -deficient muscle. Aside from changes in basic amino acids, low-K + skeletal muscle had increased amounts of threonine, serine, glutamine and citrulline; there were decreased concentrations of isoleucine plus leucine, valine, alanine and aspartic acid. No comparable pattern of amino acid changes were observed in normal rats with comparably reduced pH 1 or elevated pH e induced by changing pCO 2 . These findings indicate that altered pH i or pH e have no direct influence on free amino acid movements across rat skeletal muscle cells in vivo.

Studies on the hydrolytic action of pronase on derivatized and non-derivatized proteins

1. 1. The products of pronase hydrolysis of native, oxidized, dinitrophenylated, and dinitrophenylated-oxiodized RNAase (polyribonucleotide 2-oligonucleotidotransferase (cyclizing), EC 2.7.7.16) were fractionated by means of silica-gel-column chromatography of their 2,4-dinitrophenyl derivatives. 2. 2. With the exception of glycine and proline, most of the amino acids, including asparagine, glutamine and methionine sulfone, were found to be well liberated. 3. 3. Pronase action on a dinitrophenylated protein yielded ϵ-DNP-lysine but not O-DNP-tyrosine or imidazole-DNP-histidine. 4. 4. It was pointed out that the introduction of toluene into the solvent system eliminates the need for preliminary extraction procedures commonly employed for the silica gel column chromatography of DNP derivatives.

Muscle Cell pH in Relation to Chronicity of Potassium Depletion

Summary Intracellular hydrogen ion changes in skeletal muscle from rats on a low-K regimen for 14 or 35 days were determined by DMO distribution. The objective was to determine whether changes in intracellular pH, plasma pH and plasma bicarbonate concentration would parallel the Na plus K deficit in K-deficient muscle. The results of this study were interpreted as indicating that the increased acidity in skeletal muscle from K-deficient rats is apparently related to the chronicity of K restriction but totally unrelated to the unequal replacement of muscle K loss by Na gain.

Effect of altered plasma pCO2 on intracellular pH during potassium deficiency.

Summary The plasma pCO2 of control and dietary K-deficient rats was mechanically altered between 20 and 90 mm Hg. The object was to compare the intracellular pH and HCO3 content of control and low-K skeletal muscle at identical pressures of plasma pCO2. This made it possible to study the intracellular pH and HCO3 changes associated with dietary K depletion without complications due to plasma pCO2 changes. The data indicate that the intracellular acidity of low-K skeletal muscle from dietary depleted rats results mainly from the conditions imposed by the low-K regimen. The results also show that the in vivo buffer capacity of low-K skeletal muscle is significantly less (P<.01) than the buffer capacity of control skeletal muscle.

Intracellular pH changes associated with protein and potassium deficiency

Abstract Skeletal muscle Na + and K + content remained essentially unchanged when normal rats were provided a low-K + , protein-free diet for 35 days. Animals subsequently given a diet deficient only in K + for 48 hours rapidly lost muscle K + which was only partially compensated by Na + gain. This created an intracellular Na + plus K + deficit comparable to that observed when normal rats are given a K-deficient diet for several weeks. Despite the rapidly produced intracellular cation deficit, there was hardly any change in muscle cell pH during the 48-hour, low-K + regimen. This and other evidence indicate that the proposed exchange of skeletal muscle K + for extracellular H + is not the cause of the intracellular acidity found in association with K + -deficiency in the rat.

DISTRIBUTION OF 5,5-DIMETHYL-2,4-OXAZOLIDINEDIONE (DMO) BETWEEN PLASMA AND ERYTHROCYTES.

Summary In vitro experiments on rat blood to which DMO was added indicated that the DMO-becomes distributed between the plasma and the erythrocytes in a manner similar to a Donnan distribution. It was concluded that DMO cannot serve as a test substance for determination of the erythrocyte pH employing the principle proposed by Waddell and Butler.

Liver Glycogen in Potassium-Deficient Rats Following Carbohydrate and Alanine Administration, With and Without Potassium

Summary Changes in liver glycogen, water and potassium were compared in normal and potassium-deficient rats following administration of glucose, fructose and alpha-alanine, with and without potassium. Potassium-deficient rats deposited liver glycogen equally as well as normal rats. The simultaneous increases in liver water and potassium were likewise similar in the 2 groups of animals. No significant differences in changes in liver glycogen, water or potassium were noted with simultaneous administration of potassium.

The Interaction∗ between K Depletion and CO2 Inhalation on Intracellular Bicarbonate Content

Summary Intracellular bicarbonate content ([HCO3 -] i ) of rat skeletal muscle was derived from CO2 distribution in animals subjected to CO2 inhalation and K deficiency applied singly and together. The objectives were to determine (i) whether or not [HCO3 -] i would be reduced in acidotic, low-K muscle, and (ii) whether the [HCO3 -] i increase due to CO2 inhalation would be the same in normal and K-deficient animals. There was a 20% reduction in the CO2-derived [HCO3 -] i of low-K muscle. A 20% reduction was also obtained when deriving [HCO3 -] i from DMO pH i . The [HCO3 -] i increment due to CO2 inhalation was sufficiently less in low-K muscle to yield, upon analysis of variance, a statistical interaction between the two stresses applied. This interaction was indicative of less buffering by low-K muscle. The data strongly suggest that the acidotic, low-K cell is defending against H+ whose origin is metabolic.