Dual effect of polyphenolic compounds on cardiac Na+/K+-ATPase during development and persistence of hypertension in ratsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research.

The enzyme kinetics of cardiac Na+/K+-ATPase were used for characterizing the ATP- and Na+-binding sites after administration of red wine polyphenolic compounds (Provinol) during developing and sustained hypertension. Hypertension was induced in rats (LN group) by the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 40 mg·kg–1·day–1). Provinol (40 mg·kg–1·day–1) was applied during developing hypertension (LNPF4 group) and sustained hypertension (LNPF7/3 group). Provinol reduced the number of active Na+/K+-ATPase molecules in cardiac tissue, as indicated by decreased Vmax values (by 33% in LNPF4 and 26% in LNPF7/3 compared with LN). Concerning qualitative properties of the enzyme, Provinol induced different effects on the ATP- and Na+-binding sites of Na+/K+-ATPase. The ATP-binding site was impaired by Provinol, as indicated by increased Km value (by 52% in LNPF4 vs. LN), suggesting worsened utilization of substrate by the enzyme. In sustained hypertension, however, Provinol had no..., On a utilisé la cinétique enzymatique de la Na+/K+-ATPase pour caractériser les sites de liaison de l’ATP et du Na+ après l’administration de composés polyphénoliques du vin rouge (Provinol) durant l’installation de l’hypertension et l’hypertension confirmée. On a induit l’hypertension chez des rats (groupe LN) par le biais de l’inhibiteur de la monoxyde d’azote synthase, l-NAME (40 mg·kg–1·jour–1). On a administré le Provinol (40 mg·kg–1·jour–1) durant l’installation de l’hypertension (LNPF4) et durant l’hypertension confirmée (LNPF7/3). Le Provinol a réduit le nombre de molécules actives de la Na+/K+-ATPase dans le tissu cardiaque, comme l’indique la diminution des valeurs de Vmax (de 33 % chez LNPF4 et de 26 % chez LNPF7/3 comparativement à celles du groupe LN). Du point de vue qualitatif, le Provinol a induit divers effets sur les sites de liaison de l’ATP et du Na+ de la Na+/K+-ATPase. Il a altéré le site de liaison de l’ATP, comme le montre l’augmentation de la valeur de Km (de 52 % chez le groupe L..

Effect of the Pyridoindole Antioxidant Stobadine on the Cardiac Na + ,K + -ATPase in Rats with Streptozotocin-Induced Diabetes

Abstract. In the present study we examined the effect of dietary supplementation with the pyridoindole antioxidant stobadine on functional properties of the cardiac Na + ,K + -ATPase in diabetic rats. Diabetes lasting sixteen weeks which was induced by a single i.v. dose of streptozotocin (55 mg·kg −1 ) was followed by decrease in the enzyme activity. Evaluation of kinetic parameters revealed a statistically significant decrease in the maximum velocity (V max ) (32 % for ATP-activation, 33 % for Na + -activation), indicating a diabetes-induced diminution of the number of active enzyme molecules in cardiac sarcolemma. The ATP-binding properties of the enzyme were not affected by diabetes as suggested by statistically insignificant changes in the value of Michaelis-Menten constant, K M(ATP) . On the other hand, the affinity to sodium decreased as suggested by 54 % increase in the K M(Na + ) value. This impairment in the affinity of the Na + -binding site together with decreased number of active Na + ,K + -ATPase molecules are probably responsible for the deteriorated enzyme function in hearts of diabetic animals. Administration of stobadine to diabetic rats dramatically improved the function of cardiac Na + ,K + -ATPase with regard to Na + -handling, as documented by statistically significant elevation of V max by 66 and 47 % decrease in K M(Na + ) . Our data suggest that stobadine may prevent the diabetes-induced deterioration of cardiac Na + ,K + -ATPase, thus enabling to preserve its normal function in regulation of intracellular homeostasis of Na + and K + ions

Quantitative Relationship Between the Protein Secondary Structure in Cardiac Sarcolemma and the Activity of the Membrane-bound Ca 2+ -ATPase

Abstract. In the absence of ATP, increasing concentrations of calcium within a range between 0.1-8.0 mmol. I" 1 gradually lowered the a-helix content of proteins in rat heart sarcolemma requiring no energy supply. In the presence of ATP, similar concentrations of calcium stepwise activated the sarcolemmal low-affinity Ca 2+ -ATPase. A mathematical analysis of the data obtained revealed a quantitative relationship between calcium-induced stimulation of the Ca 2+ -ATPase activity and a diminution of the a-helix contents of membrane proteins in cardiac sarcolemma. The cooperation between changes in protein conformation and energy consumption in relation to the supposed role of low-affinity Ca 2+ -ATPase in gating the calcium channel are discussed

Effect of saliva from horse fly Hybomitra bimaculata on kinetic properties of Na,K-ATPase: possible role in regulation of relaxation

The possible involvement of salivary gland extract (SGE) from horse flies in modifying hyperpolarization and relaxation via alterations in functional properties of sarcolemmal Na,K-ATPase in the host tissue was tested in vitro by application of various amounts of SGE from Hybomitra bimaculata