Metabolic Functions of Myo-inositol

The effects of myo-inositol (inositol) deprivation on the Na+ and K+ transport system of KB cells and on the Na+- and K+- activated adenosine triphosphatase of cell-free extracts were investigated. Kinetic studies under presteady state conditions showed that inositol deprivation causes a decrease of the initial rates of K+ influx and Na+ efflux. Both the Vmax of K+ influx and the Km for K+ are decreased. The rate of ATP hydrolysis catalyzed by the membrane-bound, Na+- and K+-activated adenosine triphosphatase is greatly diminished in inositol-deficient cells. Both the Vmax and the Km values for K+ and Na+ are decreased. These changes are quantitatively identical with those observed in the case of Na+ and K+ fluxes across the plasma membrane of intact cells. Inositol-deficient cells are unable to concentrate K+ to the same extent as normal cells, but the steady state concentration of intracellular Na+ remains within normal range. The lower intracellular concentration of K+ in inositol-deficient cells is not responsible for the impaired transport of α-amino-isobutyric acid exhibited by these cells.