8-bromocyclic-gmp and 2--5--dideoxyadenosine

The nitric oxide (NO)-cGMP signaling system and cAMP system play critical roles in the formation of multiple-trial induced, protein synthesis-dependent long-term memory (LTM) in many vertebrates and invertebrates. The relationship between the NO-cGMP system and cAMP system, however, remains controversial. In honey bees, the two systems have been suggested to converge on protein kinase A (PKA), based on the finding in vitro that cGMP activates PKA when sub-optimal dose of cAMP is present. In crickets, however, we have suggested that NO-cGMP pathway operates on PKA via activation of adenylyl cyclase and production of cAMP for LTM formation. To resolve this issue, we compared the effect of multiple-trial conditioning against the effect of an externally applied cGMP analog for LTM formation in crickets, in the presence of sub-optimal dose of cAMP analog and in condition in which adenylyl cyclase was inhibited. The obtained results suggest that an externally applied cGMP analog activates PKA when sub-optimal dose of cAMP analog is present, as is suggested in honey bees, but cGMP produced by multiple-trial conditioning cannot activate PKA even when sub-optimal dose of cAMP analog is present, thus indicating that cGMP produced by multiple-trial conditioning is not accessible to PKA. We conclude that the NO-cGMP system stimulates the cAMP system for LTM formation. We propose that LTM is formed by an interplay of two classes of neurons, namely, NO-producing neurons regulating LTM formation and NO-receptive neurons that are more directly involved in the formation of long-term synaptic plasticity underlying LTM formation.

Topics: Adenylyl Cyclase Inhibitors; Animals; Bucladesine; Conditioning, Classical; Conditioning, Operant; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Dideoxyadenosine; Enzyme Activation; Gryllidae; Male; Memory; Nitric Oxide

We reported previously that increasing cAMP levels in endothelial cells attenuated ATP-induced increases in hydraulic conductivity (L(p)), and that the activation of cGMP-dependent pathways was a necessary step to increase L(p) in response to inflammatory mediators. The aim of the present study was to evaluate the role of basal levels of cAMP in microvessel permeability under resting conditions and to evaluate the cross talk between cAMP- and cGMP-dependent signaling mechanisms in regulation of microvessel permeability under stimulated conditions, using individually perfused microvessels from frog and rat mesenteries. We found that reducing cAMP levels by inhibition of adenylate cyclase or inhibiting cAMP-dependent protein kinase through the use of H-89 increased basal L(p) in both frog and rat mesenteric venular microvessels. We also found that 8-bromocAMP (8-BrcAMP, 0.2 and 2 mM) was sufficient to attenuate or abolish the increases in L(p) due to exposure of frog mesenteric venular microvessels to 8-BrcGMP (2 mM) and ATP (10 microM). Similarly, in rat mesenteric venular microvessels, application of 8-BrcAMP (2 mM) abolished the increases in L(p) due to exposure to 8-BrcGMP alone (2 mM) or with the combination of bradykinin (1 nM). In addition, application of erythro-9-(2-hydroxy-3-nonyl)adenine, an inhibitor of cGMP-stimulated phosphodiesterase, significantly attenuated both 8-BrcGMP- and bradykinin-induced increases in L(p). These results demonstrate that basal levels of cAMP are critical to maintaining normal permeability under resting conditions, and that increased levels of cAMP are capable of overcoming the activation of cGMP-dependent pathways, therefore preventing increases in microvessel permeability. The balance between endothelial concentrations of these two opposing cyclic nucleotides controls microvessel permeability, and cAMP levels play a dominant role.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adenine; Adenosine Triphosphate; Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Animals; Bradykinin; Calcium-Calmodulin-Dependent Protein Kinases; Capillaries; Capillary Permeability; Cyclic AMP; Cyclic GMP; Dideoxyadenosine; Enzyme Inhibitors; Female; Isoquinolines; Male; Mesenteric Veins; Rana pipiens; Rats; Rats, Sprague-Dawley; Receptor Cross-Talk; Sulfonamides; Venules

We have previously reported that the isolated rat branch pulmonary artery (PA) contracts when made hypoxic and that the contraction is dependent in large part on the presence of a functioning endothelium. This study tested if the hypoxic contraction was caused by reduced endothelium-derived relaxing factor (EDRF) activity. To do so we tested if chemical inhibitors of EDRF mimicked the effect of hypoxia, if PA guanosine 3',5'-cyclic monophosphate (cGMP) fell during hypoxic contraction, and if stimulation of smooth muscle cGMP attenuated hypoxic contraction. We found that the EDRF inhibitors hemoglobin and methylene blue caused a concentration-dependent increase in PA force that equaled that produced by hypoxia. PA cGMP decreased in endothelium-intact rings from 105 +/- 14 pM/g (wet wt) during normoxia to 41 +/- 9 pM/g during hypoxia. In endothelium-denuded rings normoxic cGMP was reduced to 32 +/- 10 pM/g with no further decrease during hypoxia. The endothelium-independent stimulators of cGMP, nitric oxide, and 8-bromo-cGMP, reduced maximum hypoxic contraction by 80 +/- 11 and 93 +/- 3%, respectively, whereas the endothelium-dependent stimulator acetylcholine did not. PA adenosine 3',5'-cyclic monophosphate (cAMP) fell only slightly during hypoxia and cAMP inhibitors failed to mimic the hypoxic contraction. We conclude that the hypoxic contraction of isolated rat PA is caused largely by decreased EDRF activity.

Topics: Acetylcholine; Adenosine Monophosphate; Animals; Cyclic AMP; Cyclic GMP; Dideoxyadenosine; Endothelium, Vascular; Hemoglobins; Hypoxia; In Vitro Techniques; Isomerism; Kinetics; Male; Methylene Blue; Muscle, Smooth, Vascular; Nitric Oxide; Phenylephrine; Pulmonary Artery; Rats; Rats, Inbred Strains; Thionucleotides; Vasodilation