INFLUENCE OF HYPEROSMOTIC ENVIRONMENT COMPARABLE TO THE RENAL MEDULLAUPON MEMBRANE NADPH OXIDASE OF HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Hyperosmotic environment in the renal medulla seems important for bact erial pyelonephritis because it exerts inhibitory influences upon the function of polymorphonuclear leukocytes (PMN). Urea and NaCl primaril y contribute to high osmolarity in the renal medulla. We previously re ported that PMN function was actually suppressed in phagocytosis, intr acellular bacterial killing and superoxide generation in the hyperosmo tic solution of urea and NaCl. In the present report, to verify the me chanism of this inhibitory effect, a kinetic study for NADPH oxidase i n the cell membrane, the key enzyme complex of superoxide generation, was carried out in the cell membrane-solubilizing system under the hyp erosmotic condition caused by urea or NaCl. Urea directly denaturated NADPH oxidase, and its inhibitory mechanism was reversible and uncompe titive with a decrease in V-max and K-m, while NaCl had no effect upon it, maintaining Lineweaver-Burk plots in the same position as those o f the control. This result suggests that urea at least produces an inh ibitory effect upon PMN through the direct inactivation of NADPH oxida se, although NaCl was unable to do so.