Interactions of Cyclic AMP and Its Dibutyryl Analogue with a Lipid Layer in the Aqueous Mixtures of Monoolein Preparation and Dioleoyl Phosphatidylcholine as Probed by X-Ray Diffraction and Raman Spectroscopy

Interactions of adenosine 3':5'-cyclicmonophosphate (cAMP) andN⁶,2'-O-dibutyryladenosine3':5'-cyclic monophosphate (dbcAMP) with alipid layer composed of monoolein-basedpreparation and dioleoylphosphatidylcholine (DOPC) wereinvestigated by small-angle X-raydiffraction (SAXD) and Raman spectroscopy.The reversed hexagonal (H_II)MO/DOPC/H₂O phase of 65:15:20 wt.%composition was selected as a referencesystem. SAXD revealed that entrapment (atthe expense of water) of 3 wt.% cAMP intothe reference system did not change thepolymorphic form and structural parametersof the phase. The same content of dbcAMPinduced the transition from the H_IIphase to the reversed bicontinuous cubicphase of space group Ia3d. Thistransition is explained by the increase oflipid head-group area due to thepenetration of the acylated adenine groupof dbcAMP into the polar/apolar region oflipid layer. The conclusion is supported byRaman spectroscopy, showing thedisruption/weakening of hydrogen bonding inthe MO/DOPC-based matrix at the N1- andN3-sites of the dbcAMP adenine ring. Asdistinct from dbcAMP, cAMP remains mostlyin the water channels of the H_IIphase, although the phosphate residue ofnucleotide interacts with the quaternaryammonium group of DOPC. Both nucleotidesincrease the population of gaucheisomers in the DOPC choline group.     

Adenosine 3',5'-cyclic monophosphate modulates the mitogenic responses of murine B lymphocytes

Adenosine 3',5'-cyclic monophosphate (cAMP) acts to inhibit a number of lymphocyte activities. The extent of this inhibition was tested by evaluating the effects of two cAMP-raising agents on B cell S phase entry induced by several different mitogenic regimens. It was found that both dibutyryl cAMP (dbcAMP) and isobutylmethylxanthine (IBMX) enhanced S phase entry induced by some regimens but inhibited S phase entry induced by others. The observed enhancing activity stands in contrast to the general notion of cAMP as being a "negative regulator," and it confirms that the observed inhibiting activity does not simply reflect cytotoxicity. Mitogenic regimens that appear to mimic each other, such as F(ab')2 fragments of goat anti-mouse immunoglobulin and the combination of a calcium ionophore and a phorbol ester, were distinguished by their responses to the addition of the two cAMP-raising agents. B cell responses were enhanced or inhibited even when dbcAMP was added 18-24 hr after the establishment of cultures. Cyclic AMP may regulate in a complex fashion S phase entry in cells of the immune system.     

Independent regulation of pyruvate kinase expression by cyclic AMP and prostaglandin F2 alpha in mouse mastocytoma cells

P-815 mouse mastocytoma cells express the K isozyme of pyruvate kinase and the specific activity of this enzyme is increased in response to N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate, 8-bromoadenosine 3':5'-cyclic monophosphate, cholera toxin, and epinephrine, all of which also elevate the intracellular concentration of adenosine 3':5'-cyclic monophosphate. Prostaglandin F2 alpha also increases the cellular activity of this enzyme, but does not increase the adenosine 3':5'-cyclic monophosphate levels. Under all these conditions, the increase in enzymatic activity is accompanied by an equivalent increase in the pyruvate kinase protein level. However, neither the rate of enzyme synthesis nor the level of pyruvate kinase mRNA is elevated by N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate. On the other hand, it does increase the enzyme's half-life. In contrast, prostaglandin F2 alpha increases the rate of synthesis and the level of pyruvate kinase K mRNA, but has no influence on the rate of degradation. Therefore, these cells have two mechanisms which increase pyruvate kinase K levels. One operates via an increase in cAMP level and results in a decrease in the rate of degradation, whereas the other minimizes an upsurge in cAMP levels but still increases pyruvate kinase K activity by increasing its rate of synthesis.     

Stimulation of cyclic AMP in chondrocyte cultures: effects on sulfated-proteoglycan synthesis

The effects of N6,O2'-dibutyryladenosine 3':5'-cyclic monophosphate (DBcAMP), 8-bromoadenosine 3':5'-cyclic monophosphate (8Br-cAMP), 3':5'-cyclic monophosphate (cAMP), L-isoproterenol and L-epinephrine on sulfated-proteoglycan synthesis by rabbit articular chondrocytes were compared. DBcAMP and 8Br-cAMP in the presence or absence of 3-isobutyl-1-methylxanthine (IBMX) stimulated sulfated-proteoglycan biosynthesis after 20 h of incubation. cAMP had no significant effect. Both DBcAMP and 8Br-cAMP increased the hydrodynamic size of the newly synthesized proteoglycan monomer (A1D1) relative to control cultures. By contrast, although isoproterenol and epinephrine stimulated total cAMP synthesis, neither stimulated sulfated-proteoglycan synthesis. Whereas intracellular cAMP accumulated after incubation with DBcAMP and 8Br-cAMP, this was not the case with isoproterenol whether IBMX was present or not. Thus, stimulation of sulfated-proteoglycan synthesis by cAMP analogues in chondrocyte cultures appears to be dependent on increased intracellular cAMP accumulation rather than total cAMP biosynthesis.     

Cyclic nucleotides in spinal cells.

The most striking effects of intracellular injections of adenosine 3'5'-cyclic monophosphate (cAMP) into spinal mononeurons in cats are a speeding-up of the action potential, both its rising and falling phase, and a potentiation of the after-hyperpolarization; the latter porbably indicates a marked enhancement of Ca2+ influx. In this respect, cAMP and guanosine 3'5'-cyclic monophosphate (cGMP) have similar actions, though cAMP appears to be more potent. It is suggested that through this mechanism, cyclic nucleotides may play an important role in synaptic facilitation. Changes in resting membrane potential and resistance are less conspicuous or predictable. By contrast, both agents, when injected into unresponsive cells, presumed to be neuroglia, regularly cause a drop in membrane resistance; this is associated with hyperpolarization and therefore likely to reflect an increase in membrane K+ conductance.     

Inhibition of DNA synthesis of adult rat hepatocytes in primary culture by dibutyrylcytidine 3', 5'-cyclic monophosphate

The effect of dibutyrylcytidine 3',5'-cyclic monophosphate (Bt2cCMP) on DNA synthesis of adult rat hepatocytes in primary culture was examined. Bt2cCMP caused dose-dependent inhibition of the DNA syntheses stimulated by various growth factors including human hepatocyte growth factor (hHGF). Dibutyryladenosine 3',5'-cyclic monophosphate (Bt2cAMP) inhibited the DNA synthesis more effectively than Bt2cCMP, but dibutyrylguanosine 3',5'-cyclic monophosphate (Bt2cGMP) and n-butyrate had a slight or null inhibitory effect. When added at the onset of DNA synthesis, Bt2cAMP was much less effective, but Bt2cCMP was still effective. Thus Bt2cCMP is able to inhibit growth factor-stimulated hepatocyte proliferation.     

Effects of oxytocin and methacholine on cyclic nucleotide levels of rabbit myometrium

The effects of oxytocin and methacholine on cyclic nucleotide levels in estrogen-primed rabbit myometrium were studied in the presence and absence of 1-methyl-3-isobutyl xanthine (MIX), a phosphodiesterase inhibitor. In the absence of MIX, methacholine increased guanosine 3',5'-cyclic monophosphate (cGMP) levels at a time when contraction was decreasing, but had no influence on adenosine 3',5'-cyclic monophosphate (cAMP) levels. In contrast, oxytocin did not elevate cGMP, but rapidly decreased cAMP levels. MIX (1 mM) increased both cAMP and cGMP levels. Oxytocin or methacholine further increased cGMP, indicating activation of guanylate cyclase. Oxytocin- but not methacholine-induced stimulation of guanylate cyclase was abolished in Ca2+-free solution. Oxytocin increased cAMP over the levels produced by MIX alone, whereas methacholine decreased cAMP below the MIX control values; these effects were insensitive to indomethacin. Tissue levels of cGMP and cAMP did not directly correlate with isometric tension. The results also indicate that both oxytocin and methacholine stimulate guanylate cyclase but have opposing effects on adenylate cyclase of rabbit myometrium.     

Regulation of RAW264 macrophage morphology and spreading: studies with protein kinase C activators, inhibitors and a cyclic AMP analog

Protein kinases C and A probably play important roles in membrane signal transduction. To test the role of protein kinases in macrophage spreading, we have measured cell perimeters in the absence and presence of protein kinase C activators, inhibitors and a cAMP analog. Scanning electron microscopy indicated that macrophages spread extensively in the presence of protein kinase C activators. In contrast, protein kinase C inhibitor and dbcAMP (N6-2'-O-di-butyryladenosine 3':5'-cyclic monophosphate AMP) promote a round cell morphology with many surface folds. Quantitative optical microscopy experiments showed that the maximal effects of these reagents were achieved within 30 min. The protein kinase C activators dioctonylglycerol (3 microM), phenylephrine (1 microM), and phorbol myristate acetate (1 micrograms/ml) increased macrophage spreading. Similarly, the calcium ionophore A23187 (1 microgram) increased spreading. In contrast, the protein kinase C inhibitors chlorpromazine (30 microM), sphingosine (10 microM), trifluoroperazine (10 microM), and H-7 (10 microM) significantly reduce macrophage spreading. The analog dibutyryl cAMP (30 microM) abrogates the effects of protein kinase C activators. These data suggest that protein kinase C participates in the regulation of macrophage spreading. Furthermore, the protein kinase A activator dibutyryl cAMP can inhibit the effects of protein kinase C activators.     

The effect of exogenously-supplied nucleosides and nucleotides and the involvement of adenosine 3':5'-cyclic monophosphate (cyclic AMP) in the yeast mycelium transition of Ceratocystis (= Ophiostoma) ulmi

The yeast-mycelium transition of Ceratocystis (= Ophiostoma) ulmi (NRRL 6404) was induced by exogenously-supplied nucleosides and nucleotides in defined liquid media. During the yeast-mycelium transition, intracellular adenosine 3':5'-cyclic monophosphate (cAMP) levels increased and maximum levels coincided with maximum germination. This, coupled with findings that the cAMP phosphodiesterase inhibitors, theophylline and caffeine, also induced germination and elevated levels of intracellular cAMP, indicated the involvement of cAMP in the regulation of the yeast-mycelium transition.     

Comparison of inhibition of bone resorption and escape with calcitonin and dibutyryl 3',5' cyclic adenosine monophosphate

Both parathyroid hormone (PTH) and calcitonin (CT) can increase the concentration of cyclic 3',5' adenosine monophosphate (cAMP) in fetal rat bone in organ culture. Moreover, dibutyryl cAMP (dbcAMP) can both stimulate and inhibit 45Ca release from such bones depending on dose and experimental conditions. In this study we compared dbcAMP and CT for their effects on bones pretreated with PTH. Both compounds produced transient inhibition of bone resorption followed by escape. Escape from dbcAMP was independent of prostaglandin synthesis, since it occurred both in the presence and absence of indomethacin, a prostaglandin cyclo-oxygenase inhibitor.     

Three new potential cAMP affinity labels. Inactivation of human platelet low Km cAMP phosphodiesterase by 8-[(4-bromo-2,3-dioxobutyl)thio]adenosine 3',5'-cyclic monophosphate

Three new analogues of cAMP have been synthesized and characterized: 2-[(4-bromo-2,3-dioxobutyl)thio]adenosine 3',5'-cyclic monophosphate (2-BDB-TcAMP), 2-[(3-bromo-2-oxopropyl)thio]-adenosine 3',5'-cyclic monophosphate (2-BOP-tcAMP), and 8-[(4-bromo-2,3-dioxobutyl)thio]adenosine 3',5'-cyclic monophosphate (8-BDB-TcAMP). The bromoketo moiety has the ability to react with the nucleophilic side chains of several amino acids, while the dioxobutyl group can interact with arginine. These cAMP analogues were tested for their ability to inactivate the low Km (high affinity) cAMP phosphodiesterase from human platelets. The 2-BDB-TcAMP and 2-BOP-TcAMP were competitive inhibitors of cAMP hydrolysis by the phosphodiesterase with Ki values of 0.96 +/- 0.12 and 0.70 +/- 0.12 microM, respectively. However, 2-BDB-TcAMP and 2-BOP-TcAMP did not irreversibly inactivate the phosphodiesterase at pH values from 6.0 to 7.5 and at concentrations up to 10 mM. These results indicate that although the 2-substituted TcAMP analogues bind to the enzyme, there are no reactive amino acids in the vicinity of the 2-position of the cAMP binding site. In contrast, incubation of the platelet low Km cAMP phosphodiesterase with 8-BDB-TcAMP resulted in a time-dependent, irreversible inactivation of the enzyme with a second-order rate constant of 0.031 +/- 0.009 min-1 mM1. Addition of the substrates, cAMP and cGMP, and the product, AMP, to the reaction mixture resulted in marked decreases in the inactivation rate, suggesting that the inactivation was due to reaction at the active site of the phosphodiesterase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of Adenosine-3′,5′-Monophosphate as the Bacterial Attractant for Myxamoebae of Dictyostelium discoideum

Adenosine-3',5'-cyclic monophosphate was shown to be the compound found in Escherichia coli responsible for the attraction of the amoebae of the cellular slime mold Dictyostelium discoideum. A number of other nucleotides were tested and the following were active: tubercidin-3',5'-cyclic monophosphate, N(6)-2'-O-dibutyryl-adenosine-3',5'-cyclic monophosphate, 5'-methylene adenosine-3',5'-cyclic monophosphonate, guanosine-3',5'-cyclic monophosphate, uridine-3',5'-cyclic monophosphate, cytidine-3',5'-cyclic monophosphate, inosine-3',5'-cyclic monophosphate, and thymidine-3',5'-cyclic monophosphate. They were less active than adenosine-3',5'-cyclic monophosphate. It is suggested that cyclic adenosine monophosphate secreted by the bacteria is used by the amoebae as a means of sensing and orienting towards food.     

Cyclic AMP and serum arrest of the mitotic activity of human diploid fibroblasts.

Mitotic activity in confluent cultures of human diploid fibroblasts was arrested by the reduction of the serum concentration of the incubation medium to 0.5% or by the addition of 0.5 mM 6-N, 2'-O-dibutyryl-adenosine 3':5'-cyclic monophosphate (db cAMP). Under either of these conditions, cultures maintained a constant cell number for 14 days; cultures continuously exposed to medium containing 10% serum doubled their cell number during this 14-day period. The protein cotent per cell decreased by 20% when cells were maintained with 0.5% serum whereas that of cells exposed to db cAMP remained constant. Ultrastructural studies revealed that cells exposed to db cAMP exhibited a morphology typical of cells cultures with 10% serum alone, whereas cells incubated with 0.5% serum showed the ultrastructural changes in mitochondria, endoplasmic reticulum and Golgi complex previously identified with low-serum arrest. Cellular adenosine 3':5'-cyclic monophosphate (cAMP) levels remained constant during the 7-day growth period in which confluency was attained, as well as during the 14-day arrested period with 0.5% serum. These results indicated that the mitotic inhibition induced by reducing the serum concentration of the incubation medium was not mediated by increased intracellular levels of cAMP and differed from that induced by the addition of exogenous db cAMP.     

The role of intracellular cAMP in renal gluconeogenesis in view of differential action of various cAMP analogues

Effects of various cAMP analogues on gluconeogenesis in isolated rabbit kidney tubules have been investigated. In contrast to N(6),2'-O-dibutyryladenosine-3',5'-cyclic monophosphate (db-cAMP) and cAMP, which accelerate renal gluconeogenesis, 8-bromoadenosine-3',5'-cyclic monophosphate (Br-cAMP) and 8-(4-chlorophenylthio)-cAMP (pCPT-cAMP) inhibit glucose production. Stimulatory action of cAMP and db-cAMP may be evoked by butyrate and purinergic agonists generated during their extracellular and intracellular metabolism resulting in an increase in flux through fructose-1,6-bisphosphatase and in consequence acceleration of the rate of glucose formation. On the contrary, Br-cAMP is poorly metabolized in renal tubules and induces a fall of flux through glyceraldehyde-3-phosphate dehydrogenase. The contribution of putative extracellular cAMP receptors to the inhibitory Br-cAMP action is doubtful in view of a decline of glucose formation in renal tubules grown in the primary culture supplemented with forskolin. The presented data indicate that in contrast to hepatocytes, in kidney-cortex tubules an increased intracellular cAMP level results in an inhibition of glucose production.     

Differences and similarities between guanosine 3',5'-cyclic monophosphate phosphodiesterase and adenosine 3',5'-cyclic monophosphate phosphodiesterase activities in neuroblastoma cells in culture.

There are phosphodiesterase activities in both particulate and supernatant fractions which hydrolyze guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP) with an apparent Km of 2-8 muM and with an apparent Km of 44-222 muM. 4-(3-Butoxy-4-methoxybenzyl-2-imidazolidinone (RO20-1724) did not inhibit cGMP phosphodiesterase activity in homogenates of mouse neuroblastoma cells, but markedly inhibited cAMP phosphodiesterase activity. Papaverine and theophylline inhibited both cGMP and cAMP phosphodiesterase activities to about the same extent. The former was more potent than the latter. The specific activity of cGMP phosphodiesterase as a function of protein concentrations first increased and then decreased. The specific activity of cAMP phosphodiesterase decreased under a similar experimental condition.     

Determination of the rates of synthesis and degradation of adenosine 3',5'-cyclic monophosphate in Escherichia coli CRP- and CRP+ strains.

We have developed a method for estimating the rates of synthesis and degradation of adenosine 3',5'-cyclic monophosphate (cAMP) in Escherichia coli during balanced growth. Applying this method, we have found that an E. coli CRP- mutant 5333 (deficient for cAMP receptor protein) synthesizes cAMP about 25 times faster than does its CRP+ parent 1100. This accounts for the abnormally high intracellular and extracellular cAMP accumulation in 5333.     

Effect of calcium administration on renal responsiveness to parathyroid hormone in pseudohypoparathyroidism type I and II -- in comparison with normals, idiopathic and surgical hypoparathyroidism.

A 31-year-old man and a 12-year-old girl were diagnosed as pseudohypoparathyroidism (PHP) Type I because of a failure to respond to the administration of parathyroid hormone (PTH) with increased urinary excretion of phosphate and cyclic adenosine-3', 5'-monophosphate (cAMP). A 22-year-old woman was diagnosed as PHP Type II because there was no increase in the urinary excretion of phosphate despite of a marked increase in urinary cAMP excretion. With the combined calcium-PTH infusion or PTH infusion after vitamin D therapy, renal response was improved in these patients. Also dibutyryl adenosine-3'-5'-cyclic monophosphate (dbcAMP) infusion evoked an increased urinary phosphate excretion in all of the patients. The metabolic defect of our patients with PHP Type I may be caused not by a lack or defective form of PTH-sensitive receptor adenylate cyclase complex but rather by an abnormal conformation in the plasma membrane-associated receptor adenylate cyclase enzyme complex in kidney. In the patient with PHP Type II, as cAMP generation is intact, the metabolic defect might be related to a defect of calcium mobilization in renal tubular cells in response to PTH.     

Column perifusion system for steroidogenesis in isolated rat adrenal cells

A perifusion system using a plastic column into which isolated rat adrenal cells had been installed was attempted. After ACTH or cAMP was administered to the column, the corticosterone concentration in the eluate was determined. ACTH in 10(-13) and 10(-12) M did not promote corticosterone production, whereas 10(-11) and 10(-10) M showed a dose dependent production of corticosterone. By iterative infusion of 10(-11) or 10(-9) M of ACTH, very clear responses to restimulation of ACTH were noted. Following the administrations of 10(-3) or 10(-2) M of dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP), the production of corticosterone increased dose-dependently. These results suggest that this perifusion system is effective for examining the effects of ACTH or cAMP on steroidogenesis of cells.     

cGMP and cyclic nucleotide-gated channels participate in mouse sperm capacitation

During capacitation of mammalian sperm intracellular [Ca(2+)] and cyclic nucleotides increase, suggesting that CNG channels play a role in the physiology of sperm. Here we study the effect of capacitation, 8Br-cAMP (8-bromoadenosine 3',5'-cyclic monophosphate) and 8Br-cGMP (8-bromoguanosine 3',5'-cyclic monophosphate) on the macroscopic ionic currents of mouse sperm, finding the existence of different populations of sperm, in terms of the recorded current and its response to cyclic nucleotides. Our results show that capacitation and cyclic nucleotides increase the ionic current, having a differential sensitivity to cGMP (cyclic guanosine monophosphate) and cAMP (cyclic adenosine monophosphate). Using a specific inhibitor we determine the contribution of CNG channels to macroscopic current and capacitation.     

Evidence against the presence of 3',5'-cyclic adenosine monophosphate and relevant enzymes in Lactobacillus plantarum

Analysis of cells of Lactobacillus plantarum, starved or undergoing induction, showed no 3', 5'-cyclic adenosine monophosphate (cAMP). Neither adenyl cyclase nor 3', 5'-cAMP phosphodiesterase was detected in extracts. Extracts of L. plantarum did not inhibit these two enzymes of Escherichia coli K-12, strain W1435. Incubation of adenosine triphosphate (ATP)-U-(14)C with cells or various cell-free fractions of L. plantarum did not produce labeled 3', 5'-cAMP. Of various 3', 5'-cyclic and acyclic nucleotides tested, only 3', 5'-cAMP, ATP, and yeast adenylic acid stimulated l-arabinose isomerase. Yeast adenylic acid was two to four times as effective as 3', 5'-cAMP or ATP. 2', 3'-cAMP was not effective.