adenosine-3--5--cyclic-phosphorothioate and Chronic-Disease

Previous studies have shown that impaired vasoconstrictor function in chronic portal hypertension is mediated via cAMP-dependent events. Recent data have implicated two small heat-shock proteins (HSP), namely HSP20 and HSP27, in the regulation of vascular tone. Phosphorylation of HSP20 is associated with vasorelaxation, whereas phosphorylation of HSP27 is associated with vasoconstriction. We hypothesized that alterations in the expression and/or phosphorylation of small HSPs may play a role in impaired vasoconstriction in portal hypertension. A rat model of prehepatic chronic portal hypertension was used. Studies were conducted in small mesenteric arteries isolated from normal and portal hypertensive rats. Protein levels of HSP20 and HSP27 were detected by Western blot analysis. Protein phosphorylation was analyzed by isoelectric focusing. HSP20 mRNA expression was determined by RT-PCR. To examine the role of cAMP in the regulation of small HSP phosphorylation and expression, we treated both normal and portal hypertensive vessels with a PKA inhibitor Rp-cAMPS. We found both an increased HSP20 phosphorylation and a decreased HPS20 protein level in portal hypertension, both of which were restored to normal by PKA inhibition. However, PKA did not change HSP20 mRNA expression. We conclude that decreased HSP20 protein level is mediated by cAMP-dependent pathway and that impaired vasoconstrictor function in portal hypertension may be partially explained by decreased expression of HSP20. We also suggest that the phosphorylation of HSP20 by PKA may alter HSP20 turnover.

Topics: Animals; Chronic Disease; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Heat-Shock Proteins; HSP20 Heat-Shock Proteins; HSP27 Heat-Shock Proteins; Hypertension, Portal; Mesenteric Arteries; Muscle Proteins; Muscle, Smooth, Vascular; Neoplasm Proteins; Phosphorylation; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; RNA, Messenger; Thionucleotides; Vasoconstriction

Injured dorsal root ganglion (DRG) neurons often develop adrenergic sensitivity. To investigate the mechanisms of this phenomenon, the effects of norepinephrine (NE) on membrane potential of large- and medium-sized A-type neurons from chronically compressed DRG were recorded electrophysiologically in vitro. NE induced a depolarization in both control (26/36) and injured (56/62) neurons, whereas the incidence and amplitude of NE-induced depolarization in the injured neurons were significantly higher than that in controls. Following NE-induced depolarization, a subthreshold membrane potential oscillation (SMPO) was triggered or enhanced that initiated or increased repetitive firing in a fraction of injured neurons (15/56). After the SMPO was selectively abolished by application of tetrodotoxin (TTX), NE-induced depolarization failed to produce repetitive firing, even with a greater depolarization. Application of Rp-cAMPS (500 microM), a selective inhibitor of protein kinase A (PKA), decreased both SMPO and repetitive firing evoked by NE application or by intracellular current injection. Conversely, Sp-cAMPS (500 microM), a PKA activator, had a facilitating effect on both the SMPO and the repetitive firing. These results strongly suggest that a PKA mediated triggering and enhancement of SMPO may be responsible for the excitatory effects of NE on sensory neurons in neuropathic rats.

Topics: Animals; Chronic Disease; Cyclic AMP; Differential Threshold; Enzyme Inhibitors; Female; Ganglia, Spinal; Male; Membrane Potentials; Nerve Compression Syndromes; Neurons; Norepinephrine; Oscillometry; Rats; Rats, Sprague-Dawley; Tetrodotoxin; Thionucleotides

Protein kinase A (PKA) can play a critical role in the modulation of neuronal excitability. We examined the role of PKA in the modulation of abnormal spontaneous activity (SA) originating from the chronically compressed dorsal root ganglion (CCD). The L(4) and L(5) dorsal root ganglia (DRGs) were compressed by inserting a stainless steel rod into each corresponding intervertebral foramen. After 1-14 postoperative days, SA in DRG neurons with myelinated axons was recorded in vitro from teased dorsal root microfilaments. Rp-cAMPS (5-500 microM), a specific inhibitor of PKA, caused a dose-dependent decrease in the discharge rate of SA when topically applied to the DRG. The highest dose completely blocked the SA, but not the conduction of action potentials. H89 (10 microM), another PKA inhibitor, also markedly decreased SA. Sp-cAMPS (500 microM), a specific activator of PKA, increased the discharge rate of SA in all injured units tested, but did not trigger firing in silent neurons. Okadaic acid (0.1 microM), a protein phosphatase inhibitor, and forskolin (1 microM), an adenyl cyclase activator, each significantly increased the discharge rate of SA. These results strongly suggest that PKA modulates the SA in injured DRG neurons with myelinated axons.

Topics: Action Potentials; Animals; Chronic Disease; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Enzyme Inhibitors; Ganglia, Spinal; Male; Nerve Compression Syndromes; Neurons; Rats; Rats, Sprague-Dawley; Thionucleotides