Metabolic Functions of Myo-inositol

The effects of myo-inositol deficiency on amino acid transport and accumulation by KB cells were studied with the aid of 14C-labeled serine, glycine, and α-aminoisobutyric acid. Kinetic studies of influx of these amino acids showed that inositol deficiency decreases the initial influx rate and the Vmax of all three amino acids. The magnitude of this decrease depends on the severity of inositol deficiency. The steady state accumulation levels of these amino acids established after influx were significantly reduced in deficient cells. Similarly the steady state distribution ratios of α-aminoisobutyric acid, established after influx or following efflux from previously loaded cells, were decreased in inositol-deficient cells, the magnitude of this decrease becoming larger as deficiency progressed. The relative efflux rate of α-aminoisobutyric acid from previously loaded cells was the same in both normal and deficient cells, and it was directly proportional to the initial intracellular concentration of α-aminoisobutyric acid. Inositol-deficient cells were unable to increase the steady state accumulation levels of α-aminoisobutyric acid to the same extend as normal cells, in response to increasing concentrations of extracellular Na+. No differences were observed between normal and deficient cells in their ability to accumulate α-aminoisobutyric acid at different concentrations of extracellular K+ or Ca++. It is concluded that inositol deficiency impairs the mechanism responsible for the uptake and accumulation of amino acids by KB cells.