AJP - Cell Physiology, Vol 262, Issue 6 C1364-C1370, Copyright © 1992 by American Physiological Society
Activated neutrophils inhibit Na(+)-K(+)-ATPase in canine renal basolateral membrane
C. M. Julin, J. J. Zimmerman, V. Sundaram and M. C. Chobanian
Department of Pediatrics, University of Wisconsin School of Medicine, Madison 53792.
To examine the effects of activated neutrophils (PMNs) on
Na(+)-K(+)-ATPase, phorbol 12-myristate 13-acetate (PMA)-stimulated PMNs
were incubated with canine renal cortical basolateral membrane (BLM), and
BLM ouabain-sensitive Na(+)-K(+)-ATPase activity was subsequently
quantified. Na(+)-K(+)-ATPase activity decreased to 40.0 +/- 8.7% (SE) of
control in the presence of activated PMNs, from 0.89 +/- 0.12 to 0.34 +/-
0.05 mumol Pi.mg protein-1.min-1. This inhibition coincided with a decrease
in the apparent Michaelis constant (Km) for ATP from 0.18 +/- 0.02 to 0.05
+/- 0.01 mM. Inclusion of catalase (CAT) and superoxide dismutase (SOD) in
the BLM/PMN/PMA incubation mixture resulted in partial preservation of
enzyme activity, with an increase to 57.0 +/- 4.6% of control with CAT
alone and to 70.0 +/- 5.3% with both CAT and SOD. SOD alone had no
protective effect. Neither the myeloperoxidase inhibitor azide nor the
hypochlorous acid scavenger L-methionine preserved enzyme activity.
Hydroxyl radical scavengers and iron chelators were also ineffective in
attenuating Na(+)-K(+)-ATPase inhibition by activated PMNs. These results
indicate that activated PMNs mediate a decrease in BLM Na(+)-K(+)-ATPase
activity characterized by a reduction in maximum velocity and Km for ATP
that appears to be mediated in part by reactive oxygen metabolites.
