Metabolic Functions of Myo-inositol

VIII. ROLE OF INOSITOL IN Na⁺-K⁺ TRANSPORT AND IN Na⁺- AND K⁺-ACTIVATED ADENOSINE TRIPHOSPHATASE OF KB CELLS

From the ¹ From the Department of Biochemistry, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104

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 V_max of K⁺ influx and the K_m 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 V_max and the K_m 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 -amino-isobutyric acid exhibited by these cells.