Biomedical subjects

C A Holmquist

Publications and source records attributed to C A Holmquist.

4 recordsLinked to original sources

PubMed1985

Adenosine formation and release from neonatal-rat heart cells in culture.

The incorporation of [3H]adenosine (10 microM) into neonatal-rat heart cell nucleotides was inhibited in a concentration-dependent manner, such that 50% inhibition was obtained with 0.75 microM-dipyridamole, 0.26 microM-hexobendine or 0.22 microM-dilazep. Adenosine formation was accelerated 2.5-fold to 2.1 +/- 0.3 nmol/10(7) cells in 10 min when cells were incubated with a combination of 30 mM-2-deoxyglucose and 2 micrograms of oligomycin/ml. Of the newly formed adenosine, 6 +/- 2% was in the cells. Dipyridamole, hexobendine or dilazep (10 microM) increased the amount of adenosine in the cells and decreased that in the medium such that 45-50% of the newly formed adenosine was in the cells. Antibodies which inhibited ecto-5'-nucleotidase by 98.7 +/- 0.3% did not alter the rate of adenosine formation or its distribution between cells and medium. We conclude that adenosine was formed in the cytoplasm during catabolism of cellular ATP and was released via the dipyridamole-sensitive symmetric nucleoside transporter.

5'-Nucleotidase↗

PubMed1985

Adenosine formation. Evidence for a direct biochemical link with energy metabolism.

The increase in tissue and coronary effluent adenosine concentration in hearts undergoing net ATP breakdown results from an accelation of adenosine formation and not from an inhibition of adenosine inactivation. Adenosine formation takes place inside intact isolated cells by a pathway distinct from the cell membrane 5'-nucleotidase, which hydrolyzes only extracellular AMP. Both the magnitude and the variation in the rate of adenosine formation in polymorphonuclear leukocytes undergoing ATP catabolism can be accounted for by the properties of a cytosolic 5'-nucleotidase that is also present in heart. This enzyme, which is allosterically activated by ATP-Mg and inhibited by Pi, provides a direct biochemical link between the energy status of the cell and the rate of adenosine formation. The actions of adenosine to dilate coronary arterioles, antagonize the inotropic effect of catecholamines, and reduce sympathetic-nerve firing would ameliorate the original energy imbalance. Adenosine may therefore function in heart and also in brain, skeletal muscle, kidney, and adipose tissue as a "retaliatory metabolite" that protects the cell against excessive external stimulation.

5'-Nucleotidase↗

PubMed1983

The control of adenosine concentration in polymorphonuclear leucocytes, cultured heart cells and isolated perfused heart from the rat.

Rat polymorphonuclear leucocytes or neonatal-rat heart cells in culture were treated with 2'-deoxycoformycin and 5-iodotubercidin at concentrations that inhibited adenosine deaminase (EC 3.5.4.4) and adenosine kinase (EC 2.7.1.20) inside the intact cells, and the rate of adenosine accumulation was determined. The basal rate of adenosine formation was 2% (polymorphonuclear leucocytes) or 9% (heart cells) of the maximal activity of adenosine kinase also measured in intact cells. Greatly increased rates of adenosine formation were observed during adenine nucleotide catabolism. This condition also led to a decrease in adenosine kinase activity. When isolated rat hearts were perfused with 5-iodotubercidin alone at a concentration which inhibited adenosine kinase, no increase in tissue or perfusate adenosine or inosine concentration was observed. However, perfusion with hypoxic buffer or infusion of adenosine into the coronary circulation at a rate (20 nmol/min) equivalent to 40% of the activity of adenosine kinase caused large increases in effluent perfusate adenosine and inosine concentrations. These data argue unanimously against the existence of a substrate cycle controlling adenosine concentration. They suggest instead that an increase in the rate of adenosine formation is the principal cause of elevations in adenosine concentration during ATP catabolism.

Adenosine↗

PubMed1981

Adenosine production inside rat polymorphonuclear leucocytes.

Adenosine synthesis was studied during 2-deoxyglucose-induced ATP catabolism in intact rat polymorphonuclear leucocytes. When both adenosine kinase (EC 2.7.1.20) and adenosine deaminase (EC 3.5.4.4) were selectively inhibited, adenosine accumulated. Adenosine formation took place inside the intact cells by a metabolic pathway independent of the ecto-5'-nucleotidase (EC 3.1.3.5). Distinct metabolic pathways are proposed for adenosine production from intracellular or extracellular nucleotides.

5'-Nucleotidase↗