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 5(th)-8(th) 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 N+-binding site of Na,K-ATPase molecules was probably responsible for the deteriorated enzyme function in the kidneys of quercetin treated animals.