It was previously shown that 4 hours´ lasting inhibition of nitric oxide synthesis by administration of an L-arginine analogue, the NG-nitro-L-arginine methyl ester (L-NAME) changed the affinity of the Na-binding site of Na,K-ATPase thus resulting in elevation of enzyme activity especially at higher concentrations of sodium. Using the same experimental model, we focused our attention in the present study to the question of binding of ATP to the enzyme molecule in the left ventricle (LV), ventricular septum (S) and the right ventricle (RV) of the dog heart. Activation of the enzyme by increasing concentrations of ATP revealed a significant increase of the Vmax only in septum (by 38 %). The KM increased significantly in septum (by 40 %) and in left ventricle (by 56 %) indicating an altered sensitivity of the ATP-binding site of Na,K-ATPase in the hearts of NO-deficient animals. The alterations of Na,K-ATPase in its ability to bind and hydrolyze ATP are localized to the tissue surrounding the cavity of the left ventricle., N. Vrbjar, M. Strnisková, O. Pecháňová, M. Gerová., and Obsahuje bibliografii
It is known that hypertension is accompanied by increased [Na+]i. The functional properties of Na,K-ATPase, which transports the Na+ out and K+ into myocardial cells during the relaxation phase, were investigated in the left ventricle (LV), septum (SV) and the right ventricle (RV) of anesthetized dogs with moderate acute blood pressure elevation elicited by short-term (4-hour) NO synthase inhibition. The NO-insufficiency was induced by administration of an L-arginine analogue, the NG-nitro-L-arginine methyl ester (L-NAME). Concerning the function of Na,K-ATPase under the conditions of lowered NO synthesis, we focused our attention to the binding of Na+ to the enzyme molecule. Activation of the enzyme by increasing Na+ concentrations revealed significant changes in both the maximal velocity (Vmax) and the affinity for Na+ (KNa) in all investigated heart sections. The Vmax increased by 27 % in LV, by 87 % in SV and by 58 % in RV. The KNa value increased by 86 % in LV, by 105 % in SV and by 93% in RV, indicating an apparent decrease in the sensitivity of the Na+-binding site in the Na,K-ATPase molecule. This apparently decreased pump affinity for Na+ together with the increase of Vmax suggest that, during the short-term inhibition of NO synthesis, the Na,K-ATPase is capable of extruding the excessive Na+ from the myocardial cells more effectively at higher [Na+]i as compared to the Na,K-ATPase of control animals., N. Vrbjar, M. Strnisková, O. Pecháňová, M. Gerová., and Obsahuje bibliografii
Adiponectin belongs to the group of biologically active substances secreted by adipocytes and referred to as adipokines. Disturbances in its secretion an d/or action are thought to be involved in the pathogenesis of some metabolic diseases. However, regulation of adiponectin secretion is poorly elucidated. In the present study, short-term regulation of adiponectin secretion in primary rat adipocytes was investigated. Isolated rat adipocytes were incubated in Krebs-Ringer buffer containing 5 mM glucose and insulin alone or in the combination with epinephrine, dibutyryl-cAMP, adenosine A 1 receptor antagonist (DPCPX), palmitate, 2-bromopalmitate or inhibitor of mitochondrial electron transport (rotenone). Adipocyte exposure for 2 h to insulin (1-100 nM) significantly increased secretion of adiponectin compared with secretion observed without insulin. Furthermore, secretion of adipon ectin from adipocytes incubated with glucose and insulin was reduced by 1 and 2 μ M epinephrine, but not by 0.25 and 0.5 μ M epinephrine. Under similar conditions, 1 and 2 mM dibutyryl-cAMP substantially diminished secretion of adiponectin, whereas 0.5 mM dibutyryl-cAMP was ineffective. Secretion of adiponectin was found to be effectively decreased by DPCPX. Moreover, ad ipocyte exposure to rotenone also resulted in a substantial diminution of secretory response of adipocytes incubated for 2 h with glucose and insulin. It was also demonstrated that palmitate an d 2-bromopalmitate (0.06-0.5 mM) failed to affect secretion of leptin. The obtained results indicated that in short-term regulation of adiponectin secretion, insulin and epinephrine exert the opposite effects. These effects appeared as early as after 2 h of exposure. Moreover, deprivation of energy or blockade of adenosine action substantially decreased secretion of adiponectin., T. Szkudelski, L. Nogowski, K. Szkudelska., and Obsahuje bibliografii a bibliografické odkazy