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The effect of L-arginine on the Na+,K+-ATPase activity in rat aorta endothelium was studied at its physiological concentrations in the range of 10(-6)-10(-3) M. The enzyme activity was 35.5% increased by low concentrations of L-arginine (or=10(-5) M) and its activity was 32.3-37.1% decreased at the L-arginine concentrations of 10(-4)-10(-3) M. A similar inhibition (by 34.5-42.8%) was also found in the presence of a NO-donor nitroglycerol (10(-4)-10(-3) M). An optical isomer of L-arginine, D-arginine, at the concentrations ofor=10(-5) M also increased the enzyme activity by 37.1%, but its inhibiting effect was much less pronounced and was 15.7% at the D-arginine concentration of 10(-3) M. An inhibitor of NO-synthase, L-NAME (NG-nitroarginine, methyl ester), failed to inhibit Na+,K+-ATPase. However, the presence of L-NAME abolished the inhibition of Na+,K+-ATPase by high concentrations of L-arginine. Thus, the effect of L-arginine on the endothelial Na+-pump depended on its concentration, and it is suggested that the enzyme inhibition by high concentrations of L-arginine should be associated with activation of the endogenous synthesis of NO. |
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