In vivo effect of cyclic nucleotides on velocity and chemotaxis of neutrophil granulocytes

Neutrophil granulocytes velocity and chemotaxis were obeserved by a direct method. Only chemotaxis could be inhibited by dibutyryl Cyclic AMP, this phenomenon could be reversed by cyclic GMP.     

The effect of cyclic nucleotides on secretin secretion in canine duodenal mucosa in vitro

We examined the effects of cyclic nucleotides and calcium on secretin release from canine duodenal mucosal explants incubated in organ culture media. Time course studies revealed that at pH 7.4, 5 and 10 mM dibutyryl cyclic adenosine monophosphate (DBcAMP) increased secretin release progressively, reaching a peak at 2 hours. Two mM of DBcAMP at pH 7.4 did not increase secretin release but at pH 4.5, all 3 doses potentiated secretin release. DBcAMP-stimulated secretin release was not dependent on the influx of extracellular calcium. Graded doses of 3-isobutyl-1-methylxanthine (IBMX) did not stimulate secretin secretion but 1 mM IBMX with 2 mM DBcAMP increased secretin secretion significantly. Dibutyryl cyclic guanosine monophosphate, cholera toxin and 5'-guanylyl-imidodiphosphate (GPP(NH)p) did not stimulate basal secretion release. The release of secretin from our explants incubated at pH 7.4 was not due to specific leakage because all of our viability studies revealed that our explants were functionally intact at the end of 2 hours. Our observations suggest that cyclic nucleotides may participate in the intracellular regulation of secretin secretion.     

Saturation of anti cyclic nucleotides antibodies by endogenous cyclic nucleotides.

Rabbits immunized against cyclic AMP or cyclic GMP produce antibodies which are fully saturated by their respective endogenous cyclic nucleotides. This was proved a) in comparing radioimmunological measurements of cyclic nucleotides in antiserum and the binding site concentration determined by equilibrium dialysis, b) in showing the ineffectiveness of serum phosphodiesterase to hydrolyze the cyclic AMP present in the anti-cyclic AMP antiserum. Immunological and radioimmunological implications of this phenomenon are discussed.     

Capturing cyclic nucleotides in action: snapshots from crystallographic studies

Fifty years ago, cyclic AMP was discovered as a second messenger of hormone action, heralding the age of signal transduction. Many cellular processes were found to be regulated by cAMP and the related cyclic GMP. Cyclic nucleotides function by binding to and activating their effectors - protein kinase A, protein kinase G, cyclic-nucleotide-regulated ion channels and the guanine nucleotide-exchange factor Epac. Recent structural insights have now made it possible to propose a general structural mechanism for how cyclic nucleotides regulate these proteins.     

In vitro incorporation of LNA nucleotides

An LNA modified nucleoside triphosphate 1 was synthesized in order to investigate its potential to act as substrate for DNA strand synthesis by polymerases. Primer extension assays for the incorporation experiments revealed that Phusion High Fidelity DNA polymerase is an efficient enzyme for incorporation of the LNA nucleotide and for extending strand to full length. It was also observed that pfu DNA polymerase could incorporate the LNA nucleotide but it failed to extend the strand to a full length product.     

Effect of cyclic nucleotides in vitro assays of rat liver galactosyltransferase.

Experiments with rat liver microsomal galactosyltransferase has been developed to test the effect of cyclic nucleotides on the transfer activity. An overall stimulation is observed when cAMP or cGMP (concentration higher that 10(-6) M) are added to the incubation medium. However, more detailed experiments show that the cyclic nucleotides do not act as direct effectors of the enzyme but present the precursors degradation by the glycosylnucleotide pyrophosphatases.     

In vitro development of seminiferous tubules from immature rat testis: ultrastructural and morphometric studies

Localization of snRNA at the ultrastructural level was studied in the nucleolus of CHO cells by EM autoradiography. In conditions where snRNA U3 is the only RNA species labelled in the nucleolus, silver grains were largely found at the periphery, over the granular ribonucleoprotein component and the perinucleolar condensed chromatin; this enrichment was quantitatively significant. Inhibition of pre-rRNA synthesis with actinomycin D did not alter the concentration or the distribution of U3 inside the nucleolus. The results are consistent with the demonstration that U3 is hydrogen-bonded to 28S pre-rRNA, and thus should be found in the granular compartment where 32S-28S pre-rRNA is assembled into 55s RNP.     

In vitro interactions between membrane, hormone, and cyclic nucleotides as revealed with aequorin

Aequorin was used to study Ca²⁺ movements in an acellular plasma membrane-rich extract from starfish oocyte cortices. Adenosine cyclic nucleotides were found to release Ca²⁺ in this system and to enhance Ca²⁺ release resulting from hormonal stimulation. The natural hormone, 1-methyladenine (1-MeAde), must act directly, independently of cyclic nucleotides, since incubating the extract with phosphodiesterase does not significantly affect the response to the hormone. Moreover, this preparation responds faster to the hormone than to cyclic nucleotides.     

In vitro studies of the effect of intermittent compressive forces on cartilage cell proliferation.

Intermittent compressive (IC) forces (96 mm Hg, 0.3 Hz) inhibit by 35–60% the serum stimulated increase in ornithine decarboxylase activity (ODC) in chick embryo epiphyseal cartilage cells and rat chondrosarcoma cells. IC had no effect on mouse fibroblast L-cells ODC. The dose-response pattern of the IC effect indicated an all-or-none response with a threshold at 80 mm Hg, a pressure roughly equivalent to the in vivo weight bearing force. The k_m of the cartilage cell ODC, measured at four hours, was about 0.1 mM and was not affected by IC. The V_max, on the other hand, was significantly reduced by IC which is consistent with less enzyme or non-competitive inhibition. IC also produced a significant increase in cAMP levels in both cartilage explants and isolated cells in the presence and absence of serum and a significant reduction in ³H-thymidine incorporation into DNA. The findings show that cellular cAMP, on one hand, and ODC and DNA synthesis, on the other hand, change in opposite directions following exposure to serum and/or IC. Investigation of the IC effect on DNA synthesis in serum-deprived synchronized cartilage cells revealed that IC reduced the number of cells going into S but did not lengthen the G₁ phase. Exposure to IC early in G₁ (0–13 hours) produced the full effect, whereas IC application between 13 to 24 hours (pre S) had no effect. IC had no effect on ³H-thymidine incorporation in L-cells.     

Modulation of in vitro erythropoiesis: enhancement of erythroid colony growth by cyclic nucleotides.

Mammalian erythropoiesis, as assayed by erythroid colony formation in vitro, is enhanced by cyclic adenosine nucleotides and agents which are capable of raising intracellular cyclic AMP (cAMP) levels. With canine marrow cells as target, this enhancement was shown to be specific for cAMP and its mono- and dibutyryl derivatives. Adenosine and its derivatives, such as AMP, ADP and ATP, and other cyclic nucleotides, such as cGMP, dibutyryl-cGMP, cCMP and cIMP and sodium butyrate were inactive. The phosphodiesterase inhibitor, RO-20-1724, and the adenyl cyclase stimulator, cholera enterotoxin, both markedly increased colony numbers. Studies with tritiated thymidine showed that about 50% of the cells responding to either erythropoietin (ESF) or dibutyryl cAMP (db-cAMP) were in DNA synthesis. However, by unit gravity sedimentation velocity analysis, the peak of ESF-responsive colony forming cells sedimented more rapidly (8-7 +/- 0-2 mm/hr) than the peak of db-cAMP-responsive cells (7-5 +/- 0 mm/hr). These results demonstrate that adenyl cyclase-linked mechanisms influence in vitro erythropoietic proliferation and suggest that other hormones and simple molecules might interact with surface receptors and thus modulate the action of ESF at the cellular level.     

In vitro studies on megakaryocytes.-I-]

Normal rat's recent bone marrow has been suspended in an isoionic, oxygenated, warmed solution; platelets production by megakaryocytes has never been verified.