Amino acid content of muscle and plasma with altered pH

Abstract

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 (pHi) and an elevation of extracellular pH (pHe). The acute respiratory acidosis reduced skeletal muscle pH1 to the same extent K+-deficiency did; the respiratory alkalosis imposed elevated pHe to a level comparable with K+-deficiency. This made it possible to determine whether or not altered pH1 or pHe 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 pH1 or elevated pHe induced by changing pCO2. These findings indicate that altered pHi or pHe have no direct influence on free amino acid movements across rat skeletal muscle cells in vivo. 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 (pHi) and an elevation of extracellular pH (pHe). The acute respiratory acidosis reduced skeletal muscle pH1 to the same extent K+-deficiency did; the respiratory alkalosis imposed elevated pHe to a level comparable with K+-deficiency. This made it possible to determine whether or not altered pH1 or pHe 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 pH1 or elevated pHe induced by changing pCO2. These findings indicate that altered pHi or pHe have no direct influence on free amino acid movements across rat skeletal muscle cells in vivo.