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At least 865 records · Page 48Linked to original sources
PubMed1981

Effects of chronic digitalization on cardiac and renal Na+ + K+-dependent adenosine triphosphate activity and circulating catecholamines in the dog.

To extend our understanding of the mechanism of action of digitalis drugs, we studied electrocardiograms (ECGs), renal function, plasma concentrations of catecholamines, and myocardial and renal Na+ + K+-dependent adenosine triphosphate (Na+ + K+ ATPase) activity in chronically digitalized dogs. Five healthy, male, mongrel dogs received a therapeutic regimen of digoxin (0.1 mg/kg on day 1 in three divided doses followed by 0.025 mg/kg per day) orally for 2-4 months. This resulted in plasma digoxin concentrations of 1.1 to 4.7 ng/ml as determined by radioimmunoassay. Six control dogs received daily gelatin capsules by mouth. ECGs monitored throughout the study showed no changes. Digitalized dogs had elevated plasma norepinephrine concentrations (347 vs. 137 pg/ml in controls) and no change in plasma epinephrine concentrations. Digitalized dogs had elevated glomerular filtration rates (0.74 vs. 0.94 ml/min per g of kidney) without significant changes in renal handling of electrolytes and water. All of the above studies were done without the aid of restraining drugs or infusions. The animals were killed with an overdose of pentobarbital for in vitro studies. In digitalized dogs, microsomal Na+ + K+ ATPase-specific activity was 26 to 33% lower in the renal cortex, medulla, and papilla, and 46% lower in the cardiac left ventricle than in control dogs. Digitalization did not alter the osmolalities of renal tissues. We conclude that chronic reduction Na+ + K+ ATPase activity by one-third dose does not cause abnormalities in renal handling of electrolytes and water, and inhibition of Na+ + K+ ATPase in the left ventricular muscle by one-half is associated with no obvious ECG changes in the dog. Further, elevated plasma norepinephrine concentrations may contribute to both the therapeutic and the toxic effects of digitalis.

Animals↗
PubMed1982

Adenosine triphosphate (ATP) hydrolysis promoted by cobalt (III). Participation of polynuclear metal complexes.

Complex formation between ATP (adenosine 5'-triphosphate) and tn2COIII(aq) (tn = trimethylenediamine) and resulting hydrolysis of the ATP to ADP (adenosine 5'-diphosphate), AMP (adenosine 5'-monophosphate), PPi (pyrophosphate), and Pi (orthophosphate) have been examined by means of 31P nmr. With ATP approximately 0.1 M and tn2CoIII-(aq) up to 0.3 M, complex formation was promoted by equilibrating solutions for a period at pH 4, after which hydrolysis was allowed to proceed at each of several pHs in the range 5 to 9 prior to quenching by addition of strong base. With ATP 0.01 M and tn2CoIII(aq) up to 0.08 M, the above procedure was followed in some cases; in other experiments the pH of each ATP/tn2CoIII(aq) solution was adjusted immediately to a value in the range 5 to 9 with the remainder of the procedure as before. In most cases the hydrolysis was at 25 degrees C, but temperature dependence was also examined. The integrals for the beta-phosphorus resonance have been used to analyze for ATP in the quenched solutions; independent measurements of ATP by an enzyme/spectrophotometric method (Bergmeyer) gave similar results. Cobalt to ATP molar ratios up to 1 produce tn2CoIII-ATP as the predominant ATP complex; this 1:1 complex shows no detectable acceleration in hydrolysis compared to free ATP. Cobalt to ATP molar ratios of greater than 1 lead to complexes of type (tn2CoIII)2ATP and (tn2CoIII)3ATP, which exhibit greatly enhanced reactivity towards ATP hydrolysis. At a 2:1 molar ratio (0.1 or 0.01 M ATP), the enhancement in rate is approximately 10(5) at pH 7 where the rate is a maximum (comparison for 25 degrees C); at higher molar ratios the rate enhancements are even greater. The results support the view that effective metal ion catalysis of ATP hydrolysis requires formation of reactive species involving more than one metal ion per ATP.

Adenosine Triphosphate↗
PubMed1992

Negative modulation of human NK cell activity by purinoceptors. 1. Effect of exogenous adenosine triphosphate.

A variety of receptors, including purinergic receptors (for adenosine and adenosine nucleotides), are present on lymphoid cells. We have investigated the negative modulatory action of ATP, a high-energy purinergic compound, on the human peripheral blood natural killer (NK) cells. Micromolar doses of exogenous ATP produced a strong, direct, reversible, and dose-dependent (2.5 x 10(-5) to 8 x 10(-4) M) inhibition of NK cell-mediated cytotoxic activity in 98% of the 131 healthy donors tested. The inhibitory effect of ATP could be demonstrated in unseparated total lymphocytes and enriched NK cells (Percoll density gradient or negative selection by complement lysis) in 2- or 16-hr NK assays, at various effector:target ratios, at suboptimal and saturating concentrations of the K562 targets. The inhibitory constants ID20 and ID50 max for ATP (2 hr), which were 5.6 x 10(-5) and 8 x 10(-5) M, respectively, appear to be a relatively stable feature of an individual. The mechanism of action of ATP was also explored. It is not due to a simple chelation by ATP of the divalent cations Mg2+ and Ca2+ which play a role in the binding/lytic reactions during NK cell-mediated oncolysis. ATP treatment of lymphocytes neither nonspecifically decreased the number of viable cells nor specifically eliminated the NK cells, including their subsets, CD57+16-, CD57+16+, and CD57-16+ as revealed by immunofluorescence staining. Use of an enzyme-like kinetic approach to define the nature of ATP-induced inhibition suggests that it may be an "uncompetitive" type (Lineweaver-Burke reciprocal plot), because both Vmax (maximal velocity of oncolysis) and Km (Michaelis constant) were reduced simultaneously from 1.53 x 10(4) and 2.64 x 10(4) to 0.44 x 10(4) and 0.73 x 10(4), respectively, in presence of ATP. Other methods (Eadie-Hofstee's and Hane's equations) confirmed that ATP does elicit a qualitatively and quantitatively similar shift in these kinetic parameters. Finally, an 18-hr preactivation of effectors by interleukin 2 (IL2) resulted in partial protection from the negative modulation of NK activity by ATP, while the presence of ATP during preincubation did not interfere with the desensitizing effect of IL2. The biological relevance of these findings are discussed and it is concluded that by interacting with appropriate (non-FcRIII?) cell-surface binding sites such as P2 purinergic receptors, ATP is capable of negatively modulating the antitumor cytotoxic activity of human NK cells. This down-regulation can be partially overcome by IL2 that up-regulates NK cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗