Search PubMed⌕ Search

Biomedical subjects

J N Wells

Publications and source records attributed to J N Wells.

At least 55 records · Page 3Linked to original sources
PubMed1984

The effects of alkylated xanthines on cyclic AMP accumulation in dog thyroid slices exposed to carbamylcholine.

In dog thyroid slices stimulated by thyrotropin (TSH), activation of muscarinic cholinergic receptors leads to a decrease in cyclic AMP levels. Previous studies have established that carbamylcholine enhances cyclic GMP levels and inhibits cyclic AMP accumulation. Several experimental data have suggested that these effects are mediated by an increase in intracellular Ca2+ levels. The inhibition of cyclic AMP accumulation results in accelerated catabolism. Dog thyroid phosphodiesterase activity is due to a mixture of three enzyme forms: a calmodulin-sensitive form, a cyclic GMP-stimulated form and a cyclic AMP-specific form. This report is concerned with the comparison of the effects of several phosphodiesterase inhibitors on cell-free phosphodiestease activity and on cyclic nucleotide accumulation in intact cells. Alkylated xanthines, 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724), and 2-O-propoxyphenyl-8-azapurin-6-one (M & B 22948) were studied as inhibitors of partially purified dog thyroid phosphodieterases and for their ability to alter cyclic AMP and cyclic GMP accumulation in dog thyroid slices that had been stimulated with TSH and/or carbamylcholine. 1-Methyl-3-isobutylxanthine (MIX) and 7-benzyl MIX were the most potent inhibitors of phosphodiesterase activities in the crude soluble and particulate fractions but exhibited no selectivity for inhibiting cyclic AMP or cyclic GMP hydrolysis. In dog thyroid slices stimulated by TSH and in the absence of carbamylcholine, Ro 20-1724 and 1-isoamyl-3-isobutylxanthine (IIX) were the most effective compounds to potentiate the accumulation of cyclic AMP. The rank order of abilities to potentiate cyclic AMP accumulation in dog thyroid slices stimulated by TSH paralleled the rank order of potencies to inhibit the cyclic AMP-specific phosphodiesterase. In the presence of carbamylcholine, the observed decrease in cyclic AMP levels was attenuated by MIX, 8-methoxymethyl MIX (8-MeOMe MIX), 7-benzyl MIX, and M & B 22948, the most potent inhibitors of the calmodulin-sensitive phosphodiesterase. MIX, 8-MeOMe MIX, and 7-benzyl MIX inhibited the cyclic GMP-stimulated phosphodiesterase in the same rank order of potencies as the calmodulin-sensitive enzyme, but M & B 22948 did not significantly inhibit the cyclic GMP-stimulated enzyme activity. IIX and Ro 20-1724 did not alter the carbamylcholine-induced inhibition of cyclic AMP accumulation.(ABSTRACT TRUNCATED AT 400 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Potentiation of the effects of sodium nitroprusside and of isoproterenol by selective phosphodiesterase inhibitors.

This study identified a series of alkylated xanthines and a papaverine analogue with a range of potencies and selectivities as inhibitors of phosphodiesterases isolated from bovine coronary arteries. The abilities of these inhibitors to potentiate the relaxant effects of sodium nitroprusside (SNP) and isoproterenol were predictable from the potencies to inhibit the calmodulin-sensitive and the cyclic AMP-specific forms of phosphodiesterase, respectively. Although the xanthines potentiated the SNP- and isoproterenol-induced increases in cyclic GMP and cyclic AMP, respectively, in manners that were consistent with the involvement of the respective cyclic nucleotides in the relaxation process, the papaverine analogue did not potentiate isoproterenol-induced increases in cyclic AMP levels. These data are consistent with the hypothesis that increases in cyclic GMP levels are responsible for the relaxation of coronary artery strips by SNP. In addition, the data indicate that the calmodulin-sensitive phosphodiesterase activity does not contribute significantly to the hydrolysis of cyclic AMP in the intact bovine coronary artery smooth muscle cells.

Animals↗
PubMed1981

Inhibition of separated forms of cyclic nucleotide phosphodiesterase from pig coronary arteries by 1,3-disubstituted and 1,3,8-trisubstituted xanthines.

A series of xanthines with varied substituents in the 1, 3, and 8 positions were prepared in an attempt to understand the structure--activity relationship for alkylxanthines as inhibitors of two different forms of cyclic nucleotide phosphodiesterase. Polar substituents on the 1 or 3 position of the xanthine reduced the potency of the xanthines to inhibit both the calmodulin-sensitive and the "cyclic AMP specific" forms of phosphodiesterase. Polar substituents on the 8 position of the xanthine, other than a carboxylic acid, increased the potency to inhibit the calmodulin-sensitive form of phosphodiesterase, if they were capable of donating electrons to the xanthine nucleus. On the other hand, any substituent in the 8 position larger than H reduced the potency of the xanthines to inhibit the cyclic AMP specific form of phosphodiesterase. Topographical maps of the active sites of the two forms of phosphodiesterase are presented in summary.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1980

Characteristics of a new binding protein distinct from the kinase for guanosine 3':5'-monophosphate in rat platelets.

A new type of cyclic GMP binding protein was recently identified in our laboratory (Hamet, P. and Coquil, J.-F. (1978) J. Cyclic Nucleotide Res. 4, 281--290). The binding, recovered in the supernatant fractions, is highly specific for cyclic GMP and is clearly distinct from the binding to cyclic GMP-dependent protein kinase. Chromatography on DEAE-Sepharose separated the cyclic GMP binding protein from cyclic AMP binding, cyclic AMP-dependent kinase activities, and from guanylate cyclase. The optimal binding occurs at high pH and in the presence of thiol reagents. Several phosphodiesterase inhibitors increase the affinity of binding (Kd was 353 +/- 60 nM in the absence and 13.4 +/- 1.5 nM in the presence of 1-methyl-3-isobutyl-xanthine). The molecular weight of the binding protein was determined to be about 176,000 and the sedimentation coefficient was 6.4 S. While the binding and phosphodiesterase activities co-migrated on DEAE-Sepharose, gel filtration and sucrose gradients, certain treatments (such as increasing the concentrations of salt and heating) were able to influence one activity while having no effect on the other. Hence, the binding activity may be involved in the regulation of the activity of cyclic GMP phosphodiesterase. Since the binding protein appears to be the only 'receptor' for cyclic GMP detectable in platelets, this protein and/or its relation to cyclic GMP phosphodiesterase may play a role in the mechanism of action of cyclic GMP in platelets.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1980

Cyclic nucleotide phosphodiesterase activities from pig coronary arteries. Lack of interconvertibility of major forms.

DEAE-cellulose chromatography, with or without dithiothreitol and over a pH range of 6.0 to 8.5, resolved two phosphodiesterase activities (peaks I and II) from the soluble fraction of pig coronary arteries. The activity of peak I was increased by calmodulin (3-7-fold), whereas that of peak II was not. Chromatography of peak I on Biol-Gel A-0.5 m columns resolved two peaks of phosphodiesterase activity (peaks Ia and Ib). Peak Ia was eluted in the presence or absence of 0.1 M KCl and was relatively insensitive to calmodulin. Peak Ib was eluted only in the presence of KCl and was sensitive to calmodulin. The substrate specificity and kinetic behavior were the same for peaks I, Ia, and Ib. Repeated gel chromatography of either peak Ia or Ib, under appropriate conditions, yielded a mixture of peaks Ia and Ib. Peak Ia appears to be a reversible aggregate of peak Ib. Gel chromatography of peak II resolved only one phosphodiesterase activity, which was eluted without KCl, was highly specific for cyclic AMP, was not sensitive to calmodulin and migrated differently on the gel column than either peak Ia or Ib. Sucrose density gradient centrifugation of the soluble fraction from pig coronary arteries in the presence or absence of dithiothreitol resolved two peaks of phosphodiesterase activity (6.6 S and 3.6 S) which were similar to peaks I and II separated by DEAE-cellulose chromatography with regard to their substrate specificity and their sensitivity to calmodulin. Upon recentrifugation, each of the two peaks of phosphodiesterase activity gave a single peak of activity which migrated with the same S value as did its parent. These results indicate that the two major forms of phosphodiesterase of pig coronary arteries, which are representative of those found in many tissues, are not interconvertible in cell-free systems.

3',5'-Cyclic-AMP Phosphodiesterases↗