V. M. Varagić, M. P. Milošević, Farmakologija, Elitmedica,. Beograd, , p.  T. Struller, in Antibiotics and Chemotherapy, O. Gsell Ed.,. Karger. ASENTRA-SERTRALINE. FARMAKOLOGIJA-VARAGIC,MILOSEVIC, MATERIAL AND METHODS; THE STUDY WAS CARRIED OUT ON 28 PATIENTS. Ochsner. Mark Cooper. Baker Heart and Diabetes Institute. Jasmina Varagic. Wake Forest School of Medicine. Lawrence J Appel. Johns Hopkins Medicine.
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Farmakologija – Vladislav M. Varagić, Milenko P. Milošević – Google Books
An adequate computer programme was designed to calculate IC50 values for digoxin – induced inhibition of both isoforms. Kinetic analysis in the absence and the presence of digoxin indicated that digoxin is uncompetitive inhibitor of the high affinity enzyme isoform. The activity of this enzyme is very sensitive to the presence of some metal ions Vasic et al.
Therapeutic effect is achieved with digoxin concentration that produce a moderate enzyme inhibition about 30 per centwhereas toxic concentration inhibit over 60 per frmakologija of enzyme activity Melero et al. Furthermore, it has been shown that hypokalaemia lowers the treshold for digoxin-induced cardiac arrhythmias i. Hence, we examined the inhibitory varagoc of digoxin in the presence of below optimal potassium concentration. In addition, the extensive kinetic studies were undertaken to determine the nature of enzyme inhibition by digoxin.
The reaction was started by the addition of ATP, allowed to proceed for 10 min, and interrupted by the addition of the ice cold HCIO4 and immediate cooling on ice.
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The inorganic orthophosphate Pi liberated from the hydrolysis of ATP was measured using modified spectrophotometric procedure Vasic et al. The effect of lower potassium concentration on inhibitory efficiency of digoxin was assayed in the same standard medium containing 2 mM KC1.
Potassium concentration was optimal in the control tubes i. The degree of reactivation, dependent to the time of exposure of the sample to higher potassium concentration, was followed within the time interval of 10 to 60 minutes.
For each time point there was a control sample which served as a basis for calculating the per cent of reactivation. Kinetic parameters Kinetic experiments were carried out according to the slightly modified method of Philips Philips et al.
The initial velocities were measured in the same incubation medium, as the function of rising concentrations of MgATP2″ 0. Vmax and Km values with standard errors were derived from Lineweaver-Burck plot. As shown on Fig. It is obvious from the experimental results that the activity vs. The computer programme was made for the analysis of the data, assuming a two-site model fit. The activity of the high affinity isoenzyme was obtained by subtracting the calculated low affinity values from the experimental data.
The theoretical curves for high and low affinity enzyme isoforms are presented in Fig. Hill analysis was performed on high and low affinity parts of the inhibition curves. The half maximum inhibition concentrations ICso values as well as the values of Hill coefficients n for high and low inhibitor affinity isoforms respectively, were calculated and summarized in Table 1.
The presence of 50 mM, mM and mM KC1 in the reaction medium did not prevent digoxin – induced inhibition, i. On the contrary, having added ten times larger potassium concentration mM KC1 following the incubation period with 2. The degree of reactivation vs.
However, complete recovery was not achieved even after 60 minutes.
Картинки: Farmakologija kardiovaskularnog sistema
The kinetic properties of enzyme were determined in the presence of 2. This concentration was chosen from the inhibition curves, as the concentration that inhibit the enzyme activity in the high affinity concentration range. The dependence of the initial reaction rate vs. Kinetic constants were calculated from the experimental data according to Lineweaver-Burck transformation Fig. It is clearly apparent that digoxin decreased Km and Vmax values of the enzyme to the same extent.
The values given are the mean of at least three experiments SEM, done in duplicate. The Lineweaver-Burck transformation of the data is shown in the inset. Additionally, biphasic inhibitory curves were obtained which indicated the interference of two distinct inhibitor binding sites.
The high affinity to digoxin can be attributed to x3 – isoform, which is known to be the most sensitive to cardiac glycosides Quadri et al. Moreover, it is well known that the 0: The low affinity to digoxin can be attributed to al – isoform which shows the lowest affinity toward cardiac glycosides and is present in almost every cell Melero et al.
Our study clearly showed that the inhibitory effect of digoxin also depends on the concentration of potassium in the reaction mixture. What is more, both isoforms showed higher sensitivity towards digoxin in the presence of ten times lower potassium concentrations.
It is interesting to point out that Hill values were elevated for both isoforms in below optimal potassium concentrations in comparison to optimal conditions, which is an indication of positive cooperative effect for digoxin binding.
On the other hand, certain authors Mohamad varragic Varagic et al. Therefore, digoxin binding and its physiological effects would be augmented in the presence of low potassium concentrations. However, the fact that elevated potassium concentrations did not display protective effect in vitro, decreases the likelihood of digoxin and potassium competing for the common binding site.
Furthermore, this hypothesis is concordant with the results of kinetic analysis which confirmed that digoxin is an uncompetitive inhibitor in comparison to ATP as a substrate.
Moreover, it has been recognized that digoxin – induced inhibition is not only reversible, but also that enzyme could be reactivated by means of appropriate specific antidigoxin antibody Cano et al. Our study has shown that elevated potassium concentrations are also able to reactivate the inhibited enzyme to a certain extent, and that the reactivation is proportional to the time of exposure to increased potassium concentration.
Noprovided the financial support for this study. Dose-dependent reversal of digoxin-inhibited farmakologja of an in vitro Na,K-ATPase model by digoxin-specific antibody.
Multiplicity of of cardiac glucoside receptors in the farmkaologija.
N Eng J Med. Proc Natl Acad Sci. Cardiac glycosides and congestive heart failure. Cleavage of structural proteins during the assembly of the head of bacteriophage T4.
A short review on Cardiac Steroids and Their Aminoguanidine analogues. Quantitative analysis of drug receptor interactions: II Determination of the properties of receptor subtypes. Influence of pyridine and urea on rat brain ATPase activity. A practical curve fitting microcomputer program for the analysis of enzyme kinetic data on IBM-PC compatible computers.
Effects of rubrotoxin B on the kinetics of cationic and substrate activation of Na, K-ATPase and p-nitrophenylphosphatase. Therapy of heart failure. Rodrigez de Lorens Arnaiz, G.
Cardiotonic Activity of Semisynthetic Analogs of Digitoxigenin. Chemical aspect of the influence of cobalt ions on ATPase activty. Hypokalemia – consequences, causes and correction. J Am Coc Nephr. Primenom odgovarajuceg kompjuterskog programa izracunate su IC50 vrednosti za obe izoforme i pokazano je da je inhibitorna moc digoksina veca u uslovima snizene koncentracije jona kalijuma.
Preinkubacija sa 2,5 odnosno 10 i 25 puta vecim koncentracijama jona kalijuma od optimalnih, pre izlaganja enzima digoksinu, nije izazvala prevenciju inhibicije.
Kineticka analiza u odsustvu i prisustvu digoksina koncentracije koja odgovara IC50 vrednosti za izoformu visokog afiniteta pokazala je da je digoksin akompetitivni inhibitor enzima. Remember me on this computer. Enter the email address you signed up with and we’ll email you a reset link. Click here to sign up. Help Center Find new research papers in: