Calcium-dependent Phosphodiesterase Research Articles

Pharmacological investigation of biochemical and behavioral effects resembling Huntington's disease utilizing selective calcium and calmodulin dependent phosphodiesterase inhibitor

Pharmacological investigation of biochemical and behavioral effects resembling Huntington's disease utilizing selective calcium and calmodulin dependent phosphodiesterase inhibitor

Cyclic nucleotide signaling in polycystic kidney disease

Increased levels of 3'-5'-cyclic adenosine monophosphate (cAMP) stimulate cell proliferation and fluid secretion in polycystic kidney disease. Levels of this molecule are more sensitive to inhibition of phosphodiesterases (PDEs), whose activity far exceeds the rate of cAMP synthesis by adenylyl cyclase. Several PDEs exist, and here we measured the activity and expression of PDE families, their isoforms, and the expression of downstream effectors of cAMP signaling in the kidneys of rodents with polycystic kidney disease. We found a higher overall PDE activity in kidneys from mice as compared with rats, as well as a higher contribution of PDE1, relative to PDE4 and PDE3, to total PDE activity of kidney lysates and lower PDE1, PDE3, and PDE4 activities in the kidneys of cystic as compared with wild-type mice. There were reduced amounts of several PDE1, PDE3, and PDE4 proteins, possibly due to increased protein degradation despite an upregulation of their mRNA. Increased levels of cGMP were found in the kidneys of cystic animals, suggesting in vivo downregulation of PDE1 activity. We found an additive stimulatory effect of cAMP and cGMP on cystogenesis in vitro. Cyclic AMP-dependent protein kinase subunits Ialpha and IIbeta, PKare, the transcription factor CREB-1 mRNA, and CREM, ATF-1, and ICER proteins were upregulated in the kidneys of cystic as compared with wild-type animals. Our study suggests that alterations in cyclic nucleotide catabolism may render cystic epithelium particularly susceptible to factors acting on Gs-coupled receptors. This may account, in part, for increased cyclic nucleotide signaling in polycystic kidney disease and contribute substantially to disease progression.

Calcium-dependent phosphodiesterase 1C inhibits renin release from isolated juxtaglomerular cells

Renin release from the juxtaglomerular (JG) cell is stimulated by the second messenger cAMP and inhibited by calcium. We previously showed JG cells contain a calcium sensing receptor (CaSR), which, when stimulated, decreases cAMP formation and inhibits renin release. We hypothesize CaSR activation decreases cAMP and renin release, in part, by stimulating a calcium calmodulin-activated phosphodiesterase 1 (PDE1). We incubated our primary culture of JG cells with two selective PDE1 inhibitors [8-methoxymethil-IBMX (8-MM-IBMX; 20 microM) and vinpocetine (40 microM)] and the calmodulin inhibitor W-7 (10 microM) and measured cAMP and renin release. Stimulation of the JG cell CaSR with the calcimimetic cinacalcet (1 microM) resulted in decreased cAMP from a basal of 1.13 +/- 0.14 to 0.69 +/- 0.08 pM/mg protein (P < 0.001) and in renin release from 0.89 +/- 0.16 to 0.38 +/- 0.08 microg ANG I/mlxh(-1)xmg protein(-1) (P < 0.001). However, the addition of 8-MM-IBMX with cinacalcet returned both cAMP (1.10 +/- 0.19 pM/mg protein) and renin (0.57 +/- 0.16 microg ANG I/mlxh(-1)xmg protein(-1)) to basal levels. Similar results were obtained with vinpocetine, and also with W-7. Combining 8-MM-IBMX and W-7 had no additive effect. To determine which PDE1 isoform is involved, we performed Western blot analysis for PDE1A, B, and C. Only Western blot analysis for PDE1C showed a characteristic band apparent at 80 kDa. Immunofluorescence showed cytoplasmic distribution of PDE1C and renin in the JG cells. In conclusion, PDE1C is expressed in isolated JG cells, and contributes to calcium's inhibitory modulation of renin release from JG cells.

Hypothermic effects of alkylxanthines: evidence for a calcium-independent phosphodiesterase action

Caffeine induces a dose-dependent decrease in core body temperature in mice and the hypothermia induced by a 100 mg/kg dose of caffeine was seen to persist for greater than 160 min. Other alkylxanthines including theophylline, enprophylline, isobutylmethylxanthine and 1,3-dipropyl-7-methylxanthine also showed dose-dependent reductions in body temperature. The dose of these drugs required to reduce body temperature by 2°C was calculated and correlated with the affinities for the compounds at adenosine A 1 and A 2 receptors and their activities in inhibiting calcium dependent and independent phosphodiesterases. Significant relationships were found between the 2°C hypothermic dose (HD 2) and soluble and membrane calcium-in-dependent phosphodiesterase inhibiting activity ( r 2 s = 0.950 and 0.940, respectively). No significant relationship was seen between HD 2 and soluble calcium-dependent phosphodiesterase inhibiting activity or with A 2 adenosine receptor affinity. The relationship between HD 2 and A 1 adenosine receptor affinity ( r 2 = 0.739) did however almost reach statistical significance. These results would suggest that phosphodiesterase inhibition, instead of or in addition to adenosine receptor blockade, may play an important role in the effects of alkylxanthines on body temperature.

Parathyroid hormone stimulation of mitosis in rat thymic lymphocytes is independent of cyclic AMP.

The in vitro mitotic response of rat thymic lymphocytes to hPTH(1-34), hPTH (1-38), and 8,18 Nle hPTH(1-34) exhibits a dependency upon extracellular calcium. Removal of extracellular calcium or the addition of Verapamil (5 micrograms/ml) or trifluoroperazine (10 microM) abrogated the mitotic response. Mitogenic concentrations of 8,18 Nle hPTH(1-34) increased calcium 45 uptake from 4.49 +/- 0.25 to 8.23 +/- 0.75 pMol/10(6) cells/min. The intracellular calcium concentration, measured by Quin 2 fluorescence, also increased after addition of 8,18 Nle hPTH(1-34). Parathyroid hormone-induced activation could not be demonstrated in an otherwise responsive thymocyte membrane adenylate cyclase. In intact cells mitogenic levels of 8,18 Nle hPTH(1-34) decreased intracellular cyclic AMP content. This response was blocked by both 3-isobutyl 1-methyl xanthine and trifluoroperazine, and may indicate activation of calcium-dependent phosphodiesterase. We conclude that PTH stimulates thymic lymphocyte proliferation independently of cyclic AMP, and that changes in cellular calcium homeostasis are intimately involved in the action of PTH. In all of the assays employed, the hitherto antagonistic analogue 8,18 Nle 34 Tyr bPTH(3-34)amide proved to be an agonist. We postulate that the receptor utilized for this PTH action may not exhibit classical PTH structure-activity specificities.

P2B0428) - Effects of DSCG and Ketotifen on calcium-dependent phosphodiesterase

P2B0428) - Effects of DSCG and Ketotifen on calcium-dependent phosphodiesterase

1-(4-Aminophenyl)isoquinoline derivatives: Potent inhibitors of calcium-independent and calcium-dependent phosphodiesterases from rat cerebral cortex

The effects of a series of 1-(4-aminophenyl)isoquinoline derivatives on the activity of calcium-independent and calcium-dependent phosphodiesterases purified from rat cerebral cortex were examined. Agents were approximately equipotent ( ic 50 values, 0.2 to 25 μM) in inhibiting the calcium-dependent hydrolysis of either cyclic AMP or cyclic GMP, while they were 6–35 times more effective as inhibitors of cyclic AMP hydrolysis when compared to cyclic GMP hydrolysis using the calcium-independent enzyme. The diastereomers of 3-(carbomethoxy)propenamido demonstrated a marked difference in specificity. The cis-isomer was very potent in inhibiting cyclic AMP or cyclic GMP hydrolysis by either enzyme ( ic 50 values, 0.2 to 8 μM) while the trans-isomer was only effective in inhibiting calcium-independent cyclic AMP hydrolysis ( ic 50 values, 2.5 μM). Kinetic analyses of the type of inhibition of the calcium-dependent enzyme revealed that the various agents were competitive inhibitors of cyclic GMP hydrolysis and noncompetitive inhibitors of cyclic AMP hydrolysis. A reverse pattern of inhibition by the isoquinoline derivatives was found using the calcium-independent phosphodiesterase, i. e. noncompetitive inhibition of cyclic GMP while competitive inhibition of cyclic AMP. Inhibition of phosphodiesterases by these agents was also manifest using intact brain slices prepared from rat cerebral cortex. Thus, the agents were found to potentiate forskolin-elicited accumulations of cyclic AMP by 100–700% and increased the half-time for the decline in cyclic AMP following forskolin stimulation from 3 to 6 min.

Assessment of selective inhibition of rat cerebral cortical calcium-independent and calcium-dependent phosphodiesterases in crude extracts using deoxycyclic AMP and potassium ions.

The effects of various inhibitors on the activity of calcium-independent and calcium-dependent phosphodiesterases from rat cerebral cortex were examined. While the agents varied greatly in their relative potency, each was found to be approximately equipotent in inhibiting the calcium-dependent hydrolysis of either cyclic AMP or cyclic GMP. In contrast, the inhibitors displayed a marked substrate specificity for the calcium-independent enzyme with ratios of IC50 values for inhibition of cyclic GMP hydrolysis when compared to cyclic AMP hydrolysis in decreasing order being: ZK 62711 (much greater than 100) greater than Ro 20-1724 (much greater than 25) papaverine (13) greater than 7-benzyl IBMX (4) greater than quercetin and kaempferol (2). The differential selectivity of the inhibitors for the two enzymes was most pronounced for ZK 62711 and Ro 20-1724 which were at least 25-100-times more potent in inhibiting the calcium-independent hydrolysis of cyclic AMP when compared to the calcium-dependent hydrolysis of cyclic AMP. In contrast, 7-benzyl IBMX, kaempferol and quercetin were 8-100-times more effective as inhibitors of cyclic GMP hydrolysis by the calcium-dependent phosphodiesterase while 7-benzyl IBMX and trimazosin displayed a similar enzyme selectivity using cyclic AMP as substrate. With the exception of papaverine, all agents were competitive inhibitors of the calcium-dependent phosphodiesterase. The type of inhibition observed with the calcium-independent enzyme was dependent on the substrate employed. The specificity of potassium ions in inhibiting the activity of the calcium-dependent phosphodiesterase and deoxycyclic AMP in inhibiting the calcium-independent enzyme was found to provide a convenient means to assess the effects of agents on these activities in crude extracts of cerebral cortex.

Calcium-dependent activation and deactivation of rod outer segment phosphodiesterase is calmodulin-independent

ATP-dependent activation and deactivation of retinal rod outer segment phosphodiesterase is affected by calcium [Kawamura, S. and Bownds, M. D., J. Gen. Physiol. 77:571–591(1981)]. Our data demonstrate that although calmodulin has been found in rod outer segments [Liu, Y. P. and Schwartz, H., Biochim. Biophys. Acta 526:186–193(1978); Kohnken, R. E. et al , J. Biol. Chem. 256:12517–12522(1981)], this protein is not involved in calcium-dependent phosphodiesterase activation at light levels at which calcium clearly affects this enzyme's activity. Furthermore, calmodulin does not mediate the calcium-dependent deactivation of phosphodiesterase.

Aluminum-induced inhibition of calmodulin-regulated phosphodiesterase activity: Enzymatic and optical studies

Calmodulin, a highly conserved, endogenous calcium-binding protein, plays a major role in coordinating the effects of second messengers in response to cellular stimulation. Calcium is bound to four specific sites on calmodulin which has a molecular weight of about 17 000 [1]. Calmodulin also seems to participate in regulating the polymerization of brain microtubules whose assembly depends in part on the local level of cyclic 3′:5′-nucleotide phosphodiesterase [2]. Results presented in this communication show that aluminum binds stoichiometrically to calmodulin thereby changing its conformation which, in turn, leads to an inhibition of the calmodulin- and calcium-dependent phosphodiesterase activity. Camodulin was prepared from bovine brain acetone powder by affinity chromatography [3] with 500 mM NaCl in the elution buffers to enhance the purity of the material. All buffers and assay solutions ▪ were free from contaminating metals as analyzed on a Varian atomic absorpion spectrophotometer, model 1475. Calcium binding was measured under equilibrium dialysis conditions. The enzymatic activity was assayed as described [4]. The addition of increasing aluminum concentrations to calmodulin- and calcium-dependent phosphodiesterase produces a distinctive inhibition of the enzymatic activity (Fig. 1). In the absence of aluminum 0 percent inhibition corresponds to 0.6 nmol/ml·min cyclic GMP hydrolyzed. 50 percent inhibition of the enzymatic activity occurs at a molar ratio of 3:1 [aluminum]/[calmodulin]. The metal-induced inhibition does not appear to result simply from a displacement of calcium from its specific sites on calmodulin, as demonstrated by measuring the calcium content with atomic absorption (Fig. 1). Rather, application of aluminum causes a larger hydrophobic surface exposure of the protein as compared to that generated by calcium, as evidenced by fluorescent, hydrophobic probes. These results are in accord with those from circular dichroism experiments indicating that aluminum induces helix-coil transitions in calmodulin at stoichiometric ratios [5]. These kinds of changes in the protein may explain why the aluminumcalmodulin complex cannot interface properly with the enzymatic protein and lost at least part of its regulatory character; formation of this complex may thus be a key lesion in aluminum toxicity.

Myotonic muscular dystrophy: Calcium-dependent phosphatidate metabolism in the erythrocyte membrane

It has been suggested that the erythrocytes of myotonic dystrophy (MyD) patients have a decreased calcium-stimulated phosphatidic acid (PA) accumulation. This could be the result of a defect in the calcium-stimulated hydrolysis of the polyphosphoinositides (calcium-dependent phosphodiesterase) or in the subsequent formation of PA from its precursors (diacylglycerol kinase). In vitro assays were established for both enzymes in erythrocyte membranes. Calcium-dependent phosphodiesterase activity was assayed with both endogenous 32P-labeled erythrocyte diphosphoinositide and triphosphoinositide and with the same phospholipids isolated from rat brain. No significant differences in activity were found between MyD patients and normal controls with either method of substrate preparation. No difference in diglyceride kinase activity was found between ghosts prepared from MyD patients and normal controls. Thus, there were no differences in either of the membrane-associated enzymes of phosphatidic acid metabolism.

Alkylxanthines: Inhibition of adenosine-elicited accumulation of cyclic AMP in brain slices and of brain phosphodiesterase activity

A series of 1, 3-dialkylxanthines was examined as antagonists of adenosine-induced accumulation of cyclic AMP in guinea pig cerebral cortical slices and as inhibitors of brain phosphodiesterases. The order of potency as adenosine-antagonists was: 8-phenyltheophylline (IC 50 6 μM) > 1, 3-dibutylxanthine (IC 50 30 μM), 1, 3-dipropylxanthine > theophylline (IC 50 60 μM), 3-isobutyl-1-methylxanthine (IBMX), 1, 3, 7-triethylxanthine > 7-benzyl IBMX (IC 50 100 μM), 8-methyl IBMX > 7-benzyl-8-bromo IBMX, 9-methyl IBMX, 8-bromo IBMX, 1-isoamyl-3-isobutylxanthine. The order of potency as inhibitors of brain calcium-dependent phosphodiesterase was: 7-benzyl IBMX (IC 50 1.5 μM), 7-benzyl-8-bromo IBMX > 8-methyl IBMX (IC 50 4.5 μM) > IBMX (IC 50 7.5 μM), 8-bromo IBMX > 9-methyl IBMX (IC 50 40 μM), 1, 3, 7-triethylxanthine > 1, 3-dibutylxanthine (IC 50 100 μM), 1-isoamyl-3-isobutylxanthine > theophylline. 8-Phenyltheophylline and 1, 3-dibutylxanthine represented potent adenosine-antagonists with relatively low activity as phosphodiesterase inhibitors whereas 7-benzyl IBMX and 7-benzyl-8-bromo-IBMX were potent inhibitors of the calcium-dependent phosphodiesterase with relatively low activity as adenosine-antagonists. None of the compounds were potent inhibitors of the brain calcium-independent phosphodiesterase, although 1-isoamyl-3-isobutylxanthine might prove useful as an inhibitor of this enzyme because of its very low activity as an adenosine-antagonist.

Calcium-dependent 3‘:5‘-cyclic nucleotide phosphodiesterase. Inhibition of basal activity at physiological levels of potassium ions.

A calcium-dependent cyclic nucleotide phosphodiesterase from rat cerebrum was, in the absence of activator protein, inhibited by various monovalent cations. The inhibition was rapid, readily reversible, and concentration-dependent, with 100 mM cesium, rubidium, or potassium ion inhibiting essentially all basal enzyme activity, while 100 mM sodium or lithium ions produced only moderate inhibition. The potency of the cations in inhibiting the enzyme was Cs greater than or equal to Rb greater than K greater than Na greater than or equal to Li. Potassium ions increased the apparent Km for cyclic GMP and cyclic AMP by 3- and 5-fold, respectively. At 100 mM, the monovalent cations inhibited enzyme activated by the calcium-dependent activator by only 15 to 30%, while at 55 mM no inhibition pertained. Potassium and sodium ions at 55 mM had no effect on the calcium-independent phosphodiesterase from rat cerebrum. The results indicate that at normal intracellular concentrations of potassium ions the activity of the calcium-dependent phosphodiesterase is virtually completely dependent on the presence of calcium plus activator protein.

Phosphodiesterase activator from rat kidney cortex.

Incubation of homogenates of rat renal cortex at 4 degrees resulted in increased cAMP phosphodiesterase activity; the increase was much more rapid in hypotonic medium than in one of physiological tonicity. cAMP phosphodiesterase activity did not increase with incubation of supernatant fractions (48,000 x g, 20 min) prepared from isotonic homogenates. Extraction of the isotonic particulate fraction with hypotonic buffer released an activator which increased cAMP phosphodiesterase activity of the supernatant fraction. The kidney phosphodiesterase activator differed from a heat-stable, calcium-dependent protein activator of phosphodiesterase in that it was destroyed by heating (90 degrees for 10 min) and was not inhibited by EGTA. The phosphodiesterases of rat renal cortex were partially resolved by chromatography on DEAE-Bio-Gel, and a cAMP phosphodiesterase that is sensitive to the kidney activator was identified. This phosphodiesterase was separable from that affected by a calcium-dependent phosphodiesterase activator from bovine brain and from cGMP-stimulated cAMP phosphodiesterase. As determined by sucrose density gradient centrifugation, after incubation with the kidney activator, the activated form of phosphodiesterase had a lower sedimentation velocity than did the unactivated form.

Purification of calcium-dependent phosphodiesterases from rat cerebrum by affinity chromatography on activator protein-sepharose

Calcium-dependent activator protein purified from rat cerebrum was reacted with either N-hydroxysuccinimide-activated succinylated aminopropyl agarose or cyanogen bromide-activated Sepharose 4B. The activator protein-agarose column did not serve as an affinity adsorbant for purification of calcium-dependent phosphodiesterases from rat brain. The activator protein-Sepharose was an effective adsorbant for calcium-dependent phosphodiesterases. In the presence of calcium ions, this column selectively retained the calcium-dependent phosphodiesterases from soluble and solubilized particulate fractions from rat cerebrum. The phosphodiesterases were eluted from the column in the presence of [ethylenebis(oxyethylenenitrilo)]tetraacetic acid.

Calcium dependent phosphodiesterase activity and its activating factor (PAF) from brain: Studies on cyclic 3′,5′-nucleotide phosphodiesterase (III)

Crude extract from rat brains revealed two different activities of cyclic 3′,5′-nucleotides phosphodiesterase, namely the basal activity and the calcium dependent activity, and the total activity was shown as the sum of these two. The calcium dependent enzyme activity required for a heat-stable, nondialyzable factor (PAF) present in the brain extract. Regulation of calcium ion on the enzyme activity, in the presence of PAF, was observed within the range of pCa 5.9 to 4.9 and seems to be the physiological mechanism.