H2O2-induced uncoupling of bovine lens Na+,K+-ATPase.
A 1-hr exposure of bovine lenses in organ culture to H2O2 concentrations in the range found in the aqueous fluid of patients with cataracts inhibits 86Rb+ influx. At 1 mM H2O2, complete inhibition was observed and further investigated. Membrane permeability is slightly decreased. Although lactate concentrations increase 2-fold, lens ATP concentrations decrease approximately equal to 10%, suggesting that glycolysis may be stimulated but ATP production is not able to keep up with the demand for energy. Examination of epithelial cell Mg2+-stimulated Na+,K+-ATPase isolated from the cultured lenses indicates H2O2-induced modification. At 5 mM MgATP, ATP hydrolysis is accelerated 30%; at 3 mM MgATP, hydrolysis is normal; and at 0.75 mM MgATP, it is inhibited 75%. p-Nitrophenyl phosphate hydrolysis and eosin maleimide binding indicate that K+ control of the enzyme is modified. Thus, a very early effect of H2O2 upon the lens, well before the formation of opacity, appears to be the uncoupling of Na+ and K+ transport from ATP hydrolysis.
D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D002386:Cataract / Q000201:enzymology*; D002417:Cattle; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007908:Lens, Crystalline / Q000201:enzymology*; D012413:Rubidium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D000227:Adenine Nucleotides; D006861:Hydrogen Peroxide; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium