Effect of quercetin on kinetic properties of renal na,k-atpase in normotensive and hypertensive rats

The effect of quercetin,a plant-derived bioflavonoid with documented positive effect on the cardiovascular system,was examined after 4-week supplementation in the dose of 20 mg kg -1·day -1 to young male normotensive control (c) and to spontaneously hypertensive rats (shr) over the period of their 5th-8th week of age. the study was focused on the influence of quercetin on properties of the renal na,k-atpase,a key system in maintaining the homeostasis of sodium in the organism. spontaneous hypertension by itself enhanced the activity of na,k-atpase probably as a consequence of a higher number of active enzyme molecules,as suggested by the 15% increase of v max,along with improved affinity to atp,as indicated by the 30% decrease in the value of michaelis-menten constant k m in untreated shr vs. untreated normotensive rats. quercetin induced a decrease of na,k-atpase activity in the presence of all atp and na +concentrations investigated. evaluation of kinetic parameters resulted in a constant v max value. the atp-binding properties of the enzyme were not influenced by quercetin,as suggested by statistically insignificant changes in the value of k m both in controls and in shr. on the other hand,the affinity to sodium decreased,as suggested by an increase in the k na value by 22% and 31% in normotensive and hypertensive groups,respectively. this impairment in the affinity of the na +-binding site of na,k-atpase molecules was probably responsible for the deteriorated enzyme function in the kidneys of quercetin treated animals.