Abstract Adenylate Cyclase Research Articles

Abstract 616: Potentiation of Endothelium-Dependent Vasodilation by Adenylate Cyclase Type 9 Inactivation is Associated With Increased Endothelial Cell Signaling in Mouse Femoral Arteries

Adenylate cyclase (AC) activity in vessels is associated with vasodilation. The AC family includes 10 members of which AC9 is the least studied. We recently demonstrated that Adcy9 inactivation in mice protects from atherosclerosis in the aorta and potentiates endothelium-dependent vasodilation (EDV) to acetylcholine (ACh) in femoral arteries (FA). Our objectives were 1) to determine Adcy9 expression in FA; 2) investigate endothelial signalling pathways associated with Adcy9 inactivation-induced potentiation of ACh-induced EDV; and 3) to assess the effect of Adcy9 inactivation on EDV during flow-mediated dilation (FMD). FA were isolated from 8 to 13 week-old Adcy9- inactivated ( Adcy9 Gt ) and wild-type (WT) littermate mice. Adcy9 expression was studied in WT FA tissue section by in situ hybridization (ISH) using Adcy9 and negative control probes. Diameter of pressurized (80 mmHg) FA (internal diameter 288±3 μm) was studied in response to ACh (n=7-14) and shear stress (n=12) up to 20 dynes/cm 2 after preconstriction with phenylephrine. To study the role of endothelial signalling pathways in response to ACh-induced EDV, FA were incubated in absence or presence of inhibitors for nitric oxide (NO) synthase (L-NNA 0.1 μM), cyclooxygenase (meclofenamate 1 μM) and endothelial hyperpolarization (TRAM-34 10 μM plus apamin 0.1 μM). ISH with Adcy9 probe resulted in numerous dots in the vascular wall of the FA. Meclofenamate and the combination of TRAM-34 plus apamin decreased maximal (E max ) EDV to ACh, respectively, by 40 and 17% in Adcy9 Gt (P<0.01) but had no effect in WT mice. L-NNA reduced E max to ACh by 26% in WT (P<0.01) and 50% in Adcy9 Gt (P<0.01). Adcy9 inactivation tended to increase FMD to shear stress ranging from 6 to 20 dynes/cm 2 : At 10 dynes/cm 2 , FMD was increased from 25.4±4.9% in WT to 37.4±4.9% in Adcy9 Gt mice (P=0.083, n=12 per group). In conclusion, our data show that FA express Adcy9 and that Adcy9 inactivation increases the effects of endothelial NO, hyperpolarization and cyclooxygenase pathways in EDV. A numerical increase in FMD in Adcy9 Gt compared to WT confirms the potentiating effect of Adcy9 inactivation on EDV. The potentiation of endothelial dilatory pathways appears to be associated with the anti-atherosclerotic effects of Adcy9 inactivation.

Plant Adenylate Cyclases

Adenylate cyclase (AC) (ATP diphosphate-lyase cyclizing; EC 4.6.1.1) is a key component of the adenylate cyclase signaling system and catalyzes the generation of cyclic adenosine monophosphate (cAMP) from ATP. This review summarizes data from the literature and the authors' laboratory on the investigation of plant transmembrane (tmAC) and soluble (sAC) adenylate cyclases, in comparison with some key characteristics of adenylate cyclases of animal cells. Plant sAC has been demonstrated to exhibit similarities with animal sAC with respect to certain characteristics. External factors, such as far-red and red light, temperature, exogenous phytohormones, as well as specific triggering compounds of fungal and bacterial origin exert a significant influence on the activity of plant tmAC and sAC.

Modulation of adenyl cyclase activity in the gills of Tapes philippinarum

Adenyl cyclase (AC) plays a pivotal role in cell signaling. The AC system of bivalves has received little attention so far, and our study has been addressed to the characterization of AC properties in the gills of T. philippinarum. The enzyme showed a Km value of 0.77 mM for ATP in the presence of 5 mM Mg2+; in the absence of agonists, it was poorly affected by GTP, while it was stimulated by GTPgammaS and GppNHp up to 14-fold and 4-fold, respectively. Similarly to other invertebrates, the enzyme activity was scarcely stimulated by forskolin. The receptor agonist serotonin (5-HT) significantly stimulated the AC activity, and the pharmacological profile of the 5-HT receptor/s was as follows: (+)butaclamol > dihydroergocryptine > methysergide > prazosin > yohimbine. The AC activity was assessed in vitro in the presence of tributyltin chloride and HgCl2, which reduced the AC activity only at the highest dose tested (10-100 microM). Our data indicate the presence of a membrane-bound AC in gill membranes of T. philippinarum, coupled to Gs proteins and to a specific class of 5-HT receptors. Such receptors show a pharmacological profile slightly different from that reported for 5-HT invertebrate receptors cloned so far.

Characterization of binding of adenylate cyclase toxin to target cells by flow cytometry.

Adenylate cyclase (AC) toxin from Bordetella pertussis intoxicates eukaryotic cells by increasing intracellular cyclic AMP (cAMP) levels. In addition, insertion of AC toxin into the plasma membrane causes efflux of intracellular K(+) and, in a related process, hemolysis of sheep erythrocytes. Although intoxication, K(+) efflux, and hemolysis have been thoroughly investigated, there is little information on the nature of the interaction of this toxin with intact target cells. Using flow cytometry, we observe that binding of AC toxin to sheep erythrocytes and Jurkat T lymphocytes is dependent on posttranslational acylation of the toxin. Extracellular calcium is also necessary, with a steep calcium concentration dependence similar to that required for intoxication and hemolysis. Binding of AC toxin is concentration dependent but unsaturable up to 50 micrograms/ml, suggesting that if there is a specific receptor molecule with which the toxin interacts, it is not limiting. Visualization of cells by fluorescence microscopy supports the data obtained by flow cytometry and reveals a peripheral pattern of toxin distribution. AC toxin binds to erythrocytes at both 0 and 37 degrees C; however, the total binding at 0 degrees C is less than that at 37 degrees C. In human erythrocytes, AC toxin does not cause an increase in K(+) efflux or hemolysis. While AC toxin exhibits reduced potency to increase cAMP in these cells than in sheep erythrocytes, there is only a modest reduction in the binding of the toxin as measured by flow cytometry. Further use of this technique will provide new approaches for dynamic and functional analysis of the early steps involved in intoxication, K(+) efflux, and hemolysis produced by AC toxin.

Activity of adenylate cyclase and 5'-nucleotidase in the sensorimotor and limbic structures of the brain in rats after manipulatory training.

Adenylate cyclase (AC) and 5'-nucleotidase (NT) activities were measured in the limbic (amygdala, hippocampus) and sensorimotor (cortex, striatum) structures of the brain in three groups of rats: untrained rats and rats which were good and poor learners in training to perform movements involving pushing against an obstruction. After training, AC activity decreased in all structures studied. Activity decreased in the cortex and striatum to a greater extent in good learners, and in the amygdala in poor learners. NT activity decreased in all brain structures apart from the striatum, to a greater extent in rats which were less able to learn to produce movements involving prolonged pushing. The striatum was the only structure in which increases in NT activity occurred, from the lowest initial level in the control group. 1.0 +/- 0.04 microgram P(i)/mg protein/min, to 1.3 +/- 0.1 micrograms P(i)/mg protein/min in poor learners and to 2.0 +/- 0.1 micrograms P(i)/mg protein/min in good learners. Interhemisphere asymmetries in AC activity in the cortex and hippocampus were seen, along with an interhemisphere difference in NT activity in the amygdala. Thus, the activity of enzymes involved in adenine and cAMP biosynthesis changed in different ways in the limbic and sensorimotor structures of the brain, depending on the ability of rats to learn. The increase in NT activity after training of rats, which was limited to the striatum, may reflect a special role for the purinergic system in these structures in mediating sensation-regulated movements.

Reversible Inhibition of Adenylate Cyclase Activity in the Ischemic Myocardium

Adenylate cyclase (AC) function was studied in homogenate and particulate preparations of ischemic rat heart obtained from three models: anoxic-ischemic incubations, coronary artery ligation, and global low-flow perfusion of isolated hearts. Both basal activity and the function of AC measured in the presence of NaF (8 X 10(-3)M), Gpp(NH)p (10(-5)M), and L-(-)-isoprenaline (10(-8)-10(-4)M) were reduced to 50% of the control value in homogenates of hearts incubated under anoxic-ischemic conditions for 10 min. Comparable results were obtained with homogenates from the ischemic area 20 min after coronary artery ligation in anesthetized open-chest rats with artificial ventilation. Reduced AC activity of the anoxic-ischemic hearts was completely reversible by aerobic reperfusion, provided the ischemic period did not exceed 20 min. AC activity in homogenates of isolated hearts perfused at low-flow was not changed, indicating a nonuniform alteration of AC system in nonperfused and low-flow perfused areas of the ischemic heart. Depression of myocardial AC function during severe ischemia was avoided by reducing Ca2+ in the incubation buffer, in combination with addition of EGTA during the homogenization step, and by pretreating the animals with verapamil. It is suggested that the depressed AC function is caused mainly by an increase in intracellular Ca2+, which inhibits the enzyme at its catalytic site. A negative feedback control of AC function by Ca2+ is postulated that may operate especially in the ischemic myocardium.

Normal adenylate-cyclase activity in platelets of patients with Huntington's disease

Adenylate-cyclase activity and cyclic-AMP concentration in platelets of 7 Huntington's disease patients were found to be similar to control values.

Adenylate cyclase in regenerating tissues of the planarian Dugesia lugubris (O. Schmidt)

Adenylate cyclase (AC) was localized ultracytochemically in certain tissues of the regenerating planarian Dugesia lugubris. Studies were carried out from one hour after injury up to the 5th day of regeneration. It was found that the greatest amount of active AC appears during the initial hours of regeneration in the membranes of the muscle cells near the wound, in the epithelial cells surrounding the wound, and in rhabdite-forming cells and neoblasts.

Adenylate cyclase and guanylate cyclase activity in normal and leukemic human lymphocytes

Adenylate cyclase (AC) and guanylate cyclase (GC) activities were studied in normal B-enriched and T-enriched lymphocytes, in lymphocytes of children with acute lymphocytic leukemia (ALL), and in lymphocytes of adults with chronic lymphocytic leukemia (CLL). AC activity was greater in normal B than T lymphocytes (215 pmole/min/mg protein versus 80 pmole in the membrane-enriched fraction) and i both increased greatly after stimulation with isoproterenol and more so with prostaglandins E and F2 alpha. In leukemic lymphocytes, AC showed depressed activity (20 pmole in ALL cells and 55 pmole in CLL cells) and was less sensitive to hormonal stimulation: this loss of sensitivity occurred to a greater extent in ALL than in CLL lymphocytes. GC activity was greater in normal T than B cells (in membrane-enriched fraction: 10.2 pmole versus 5.3 pmole). It increased little with isoproterenol and prostaglandins stimulation, and much more with sodium azide and dehydroascorbic acid stimulation. GC activity was increased in both types of leukemic lymphocytes (23 pmole for ALL cells and 18 pmole for CLL cells) and was insensitive to stimulation. Possible derangement of cyclase and cyclic nucleotide regulation in leukemic cells is suggested.

Adenyl cyclase in normal and denervated skeletal muscles.

Adenyl cyclase (AC) has been studied in homogenates and crude plasma membranes from normal and denervated red and white skeletal muscle from male rats. Basal-, NaF- and epinephrine-stimulated activities were increased in homogenates of both types of muscles after nerve transection, supporting a possible role of the cAMP-AC system in the neurotrophic control of skeletal muscle. AC-specific activity was increased 10 times in crude plasmic membranes from normal muscle if compared to that of homogenate. It was decreased in crude plasmic membrane from denervated muscle. The correlation of our results with other results on cAMP concentrations and cAMP phosphodiesterase (PDE) activities in denervated muscle suggests that factors other than AC and PDE might control the synthesis and degradation of cAMP.

Effect of Salt Loading in the Rat on Adenylate Cyclase and Phosphodiesterase Activity in Kidney Cortex, Medulla and Papilla

Adenylate cyclase (AC) and phosphodiesterase (PDE) activities were studied in the cortex, medulla and papilla of the rat kidney. Sodium loading in vivo for 14 days resulted in a decrease of AC activity in the cortex, a small increase in the medulla and a substantial increase of AC activity in the papilla. Sodium loading caused reciprocal effects on PDE activity: an increase in kidney cortex and a decrease in kidney papilla. Loading of glucose in vivo or chronic administration of antidiuretic hormone in vivo did not cause the changes in AC or PDE observed after sodium loading. The possible significance of these findings is discussed.

The metabolism of cyclic-3'-5'-adenosine monophosphate (cAMP) in diseased muscle.

Adenyl cyclase (AC) and cyclic nucleotide phosphodiesterase (PDE) have been studied in muscle from patients affected with muscular and neuromuscular diseases as well as in muscle of rats after experimental denervation. A diminution of AC was observed in Duchenne's dystrophy, in neurogenic atrophies, in inflammatory forms, in myasthenia and myotonia. PDE was diminished in Duchenne's dystrophy and increased in all other diseases considered. Both enzymes were increased in rat muscle after nerve transection. The possible mechanism underlying the biochemical alterations observed are discussed including unmasking of extra-activity due to changed metabolic environment, tissue destruction and activation of lysosomal activity.