Diabetes, Vol 39, Issue 12 1472-1478, Copyright © 1990 by American Diabetes Association
Na(+)-K(+)-ATPase and changes in ATP hydrolysis, monovalent cation affinity, and K+ occlusion in diabetic and galactosemic rats
ST Tehrani, JJ Yamamoto and MH Garner
Department of Ophthalmology, California College of Medicine, University of California, Irvine 92717.
This study showed that steady-state kinetics of ATP hydrolysis by
Na(+)-K(+)-ATPase are altered in the BB Wistar diabetic rat and
experimental galactosemia. Four days after onset, this change was not
evident if NaCNBH3 was omitted during enzyme preparations (indicating
reversibility). Ninety days after onset, NaCNBH3 reduction was not
necessary to see the change in ATP hydrolysis kinetics (indicating
nonreversibility). The change in steady-state ATP hydrolysis was similar to
that reported earlier for Na(+)-K(+)-ATPase of the lens epithelium and
kidney medulla of diabetic individuals and for two in vitro glycosylation
models. Our study also showed that the affinities of Na(+)-K(+)-ATPase for
K+ are altered, and Na(+)-K(+)-ATPase-dependent K+ occlusion is inhibited
in diabetic and galactosemic animals. Because K+ occlusion is required for
efficient K+ transport, this finding supports previous in vitro studies
that indicated that glycosylation inhibits pump-dependent K+ transport.
Furthermore, our study suggested an irreversible impairment of
Na(+)-K(+)-ATPase function in the diabetic BB Wistar rat as early as 15
days after onset, even when blood glucose was maintained at 6.7 mM by daily
insulin injection.