Involvement of cyclic nucleotide-dependent protein kinases in cyclic AMP-mediated vasorelaxation

Ex vivo, in vitro, and in silico approaches to unveil the mechanisms underlying vasorelaxation effect of Mentha Longifolia (L.) in porcine coronary artery

OBJECTIVE

Mentha (M.) longifolia (L.) is traditionally used for various ailments. The current study was intended to explore the underlying vasorelaxation mechanisms of M. longifolia.

MATERIAL AND METHODS

Aqueous-methanol extract from the aerial parts of M. longifolia was prepared and subjected to activity-guided fractionation. The vasorelaxant activity was performed using porcine coronary arteries with intact and denuded endothelium. In-vitro PDE inhibitory activity of the active fraction was carried out using the radio-enzymatic assay. The active fraction was also subjected to GCMS. Docking and molecular dynamic simulation studies were also performed RESULT: We had observed that aqueous-methanolic extract induced relaxation in the coronary artery in a dose-dependent manner when the endothelium was intact and denuded. n-butanol fraction (MLB) has produced a maximum effect, and it was selected for mechanistic studies. MLB has significantly enhanced the relaxation produced by cAMP and cGMP, elevating atrial natriuretic peptide, sodium nitroprusside, isoproterenol, and forskolin. The pre-treatment with MLB inhibited the contractile response produced by KCl, U46619, and CaCl₂ in without endothelium rings. MLB has non-selectively inhibited the PDE isoforms. GCMS analysis of MLB has revealed the presence of menthol, thymol, and carvacrol in the active fraction. Docking and molecular dynamic simulation studies have indicated that thymol can be a competitive inhibitor for PDE1.

CONCLUSION

It is postulated that an n-butanol fraction of Mentha longifolia produced endothelium-independent relaxation due to increased levels of cAMP and cGMP caused by the inhibition of various PDEs.

Antihypertensive and Vasorelaxant Effects of Citrus aurantifolia Linn. Fruit: Proposed Mechanisms

Background

Citrus aurantifolia Linn. fruit, a natural dietary item, has long been used traditionally to treat hypertension in Pakistan. The current research work aims to explore the effect on blood pressure and its mechanisms.

Methods

The aqueous methanol extract of plant fruit was used to evaluate hypotensive/antihypertensive, vasorelaxation, and safety profiles. Moreover, the in vitro inhibitory effect of AMECA on phosphodiesterase was also evaluated.

Results

In hypotensive studies, extracts of Citrus aurantifolia fruit exhibited a concentration-dependent reduction in SBP, DBP, MAP, and heart rate. A similar effect has been observed on anesthetized rats, but the effects exerted by the extract were not altered significantly in the presence of L-NAME, atropine, captopril, and propranolol. Moreover, in coronary arteries, the extract significantly potentiated relaxations induced by cGMP- and cAMP-dependent relaxing agonists. When exposed to PDEs, the extract concentration dependently subdued cGMP-hydrolyzing activity of different PDEs with IC50 values of 40-130 μg/mL.

Conclusion

It is conceivable that extracts obtained from Citrus aurantifolia fruit produced hypotensive and antihypertensive effects in rats. The extract elicited endothelium-independent vasorelaxation, possibly by acting directly on smooth muscles of the coronary artery and by increasing cGMP and cAMP via nonselective inhibition of vascular PDEs.

Impaired intestinal stem cell activity in ETEC infection: enterotoxins, cyclic nucleotides, and Wnt signaling

Enterotoxigenic Escherichia coli (ETEC) in humans and animals colonizes the intestine and thereafter secrets heat-stable enterotoxin (ST) with or without heat-labile enterotoxin (LT), which triggers massive fluid and electrolyte secretion into the gut lumen. The crosstalk between the cyclic nucleotide-dependent protein kinase/cystic fibrosis transmembrane conductance regulator (cAMP or cGMP/CFTR) pathway involved in ETEC-induced diarrhea channels, and the canonical Wnt/β-catenin signaling pathway leads to changes in intestinal stem cell (ISC) fates, which are strongly associated with developmental disorders caused by diarrhea. We review how alterations in enterotoxin-activated ion channel pathways and the canonical Wnt/β-catenin signaling pathway can explain inhibited intestinal epithelial activity, characterize alterations in the crosstalk of cyclic nucleotides, and predict harmful effects on ISCs in targeted therapy. Besides, we discuss current deficits in the understanding of enterotoxin-intestinal epithelial cell activity relationships that should be considered when interpreting sequelae of diarrhea.

PDE-Mediated Cyclic Nucleotide Compartmentation in Vascular Smooth Muscle Cells: From Basic to a Clinical Perspective

Cardiovascular diseases are important causes of mortality and morbidity worldwide. Vascular smooth muscle cells (SMCs) are major components of blood vessels and are involved in physiologic and pathophysiologic conditions. In healthy vessels, vascular SMCs contribute to vasotone and regulate blood flow by cyclic nucleotide intracellular pathways. However, vascular SMCs lose their contractile phenotype under pathological conditions and alter contractility or signalling mechanisms, including cyclic nucleotide compartmentation. In the present review, we focus on compartmentalized signaling of cyclic nucleotides in vascular smooth muscle. A deeper understanding of these mechanisms clarifies the most relevant axes for the regulation of vascular tone. Furthermore, this allows the detection of possible changes associated with pathological processes, which may be of help for the discovery of novel drugs.

Therapeutic Potential of Phosphodiesterase Inhibitors for Endothelial Dysfunction- Related Diseases

Cardiovascular diseases (CVD) are considered a major health problem worldwide, being the main cause of mortality in developing and developed countries. Endothelial dysfunction, characterized by a decline in nitric oxide production and/or bioavailability, increased oxidative stress, decreased prostacyclin levels, and a reduction of endothelium-derived hyperpolarizing factor is considered an important prognostic indicator of various CVD. Changes in cyclic nucleotides production and/ or signalling, such as guanosine 3', 5'-monophosphate (cGMP) and adenosine 3', 5'-monophosphate (cAMP), also accompany many vascular disorders that course with altered endothelial function. Phosphodiesterases (PDE) are metallophosphohydrolases that catalyse cAMP and cGMP hydrolysis, thereby terminating the cyclic nucleotide-dependent signalling. The development of drugs that selectively block the activity of specific PDE families remains of great interest to the research, clinical and pharmaceutical industries. In the present review, we will discuss the effects of PDE inhibitors on CVD related to altered endothelial function, such as atherosclerosis, diabetes mellitus, arterial hypertension, stroke, aging and cirrhosis. Multiple evidences suggest that PDEs inhibition represents an attractive medical approach for the treatment of endothelial dysfunction-related diseases. Selective PDE inhibitors, especially PDE3 and PDE5 inhibitors are proposed to increase vascular NO levels by increasing antioxidant status or endothelial nitric oxide synthase expression and activation and to improve the morphological architecture of the endothelial surface. Thereby, selective PDE inhibitors can improve the endothelial function in various CVD, increasing the evidence that these drugs are potential treatment strategies for vascular dysfunction and reinforcing their potential role as an adjuvant in the pharmacotherapy of CVD.

Ion channels as effectors of cyclic nucleotide pathways: Functional relevance for arterial tone regulation

Numerous mediators and drugs regulate blood flow or arterial pressure by acting on vascular tone, involving cyclic nucleotide intracellular pathways. These signals lead to regulation of several cellular effectors, including ion channels that tune cell membrane potential, Ca²⁺ influx and vascular tone. The characterization of these vasocontrictive or vasodilating mechanisms has grown in complexity due to i) the variety of ion channels that are expressed in both vascular endothelial and smooth muscle cells, ii) the heterogeneity of responses among the various vascular beds, and iii) the number of molecular mechanisms involved in cyclic nucleotide signalling in health and disease. This review synthesizes key data from literature that highlight ion channels as physiologically relevant effectors of cyclic nucleotide pathways in the vasculature, including the characterization of the molecular mechanisms involved. In smooth muscle cells, cation influx or chloride efflux through ion channels are associated with vasoconstriction, whereas K⁺ efflux repolarizes the cell membrane potential and mediates vasodilatation. Both categories of ion currents are under the influence of cAMP and cGMP pathways. Evidence that some ion channels are influenced by CN signalling in endothelial cells will also be presented. Emphasis will also be put on recent data touching a variety of determinants such as phosphodiesterases, EPAC and kinase anchoring, that complicate or even challenge former paradigms.

Hydralazine targets cAMP-dependent protein kinase leading to sirtuin1/5 activation and lifespan extension in C. elegans

Therapeutic activation of mitochondrial function has been suggested as an effective strategy to combat aging. Hydralazine is an FDA-approved drug used in the treatment of hypertension, heart failure and cancer. Hydralazine has been recently shown to promote lifespan in C. elegans, rotifer and yeast through a mechanism which has remained elusive. Here we report cAMP-dependent protein kinase (PKA) as the direct target of hydralazine. Using in vitro and in vivo models, we demonstrate a mechanism in which binding and stabilization of a catalytic subunit of PKA by hydralazine lead to improved mitochondrial function and metabolic homeostasis via the SIRT1/SIRT5 axis, which underlies hydralazine's prolongevity and stress resistance benefits. Hydralazine also protects mitochondrial metabolism and function resulting in restoration of health and lifespan in C. elegans under high glucose and other stress conditions. Our data also provide new insights into the mechanism(s) that explain various other known beneficial effects of hydralazine.

Tambulin is a major active compound of a methanolic extract of fruits of Zanthoxylum armatum DC causing endothelium-independent relaxations in porcine coronary artery rings via the cyclic AMP and cyclic GMP relaxing pathways

BACKGROUND

Zanthoxylum armatum DC (Z. armatum), belonging to Rutaceae family, has been traditionally used for the treatment of various diseases such as hypertension, abdominal pain, headache, fever, high altitude sickness, diarrhea, dysentery, and as a tonic, condiment, and an anthelmintic treatment.

HYPOTHESIS

The present study aims to evaluate the vasorelaxant effect of a methanolic extract of the fruits of Z. armatum, isolate the active components and characterize the underlying mechanism.

STUDY DESIGN

A methanolic extract of fruits of Z. armatum was prepared and its vasorelaxant effect was studied using porcine coronary artery rings. Thereafter, the methanolic extract was analyzed, and a major compound was isolated and its structure elucidated (tambulin). Different pharmacological tools were used to characterize the vasorelaxant effect of tambulin.

RESULTS

The methanolic extract and the isolated tambulin caused similar endothelium-independent relaxations of porcine coronary artery rings with and without endothelium indicating a direct relaxing effect at the vascular smooth muscle. Tambulin did not affect the relaxation curves to the endothelium-dependent vasodilators, bradykinin and the calcium ionophore A23187 in rings with endothelium. Tambulin (1 µM) slightly but significantly shifted leftwards the concentration-relaxation curve to the endothelium-independent vasodilators, sodium nitroprusside (SNP), forskolin (FC) and isoproterenol but not those to soluble guanylyl cyclase activators (YC-1 and BAY 41-2272) and K⁺ channel openers (levcromakalim and 1-EBIO). Pretreatment with tambulin inhibited, in a concentration-dependent manner, contractions to KCl, serotonin (5-HT), CaCl₂ and U46619 in coronary artery rings without endothelium. Both the protein kinase A (H-89, 10 µM) and the protein kinase G (Rp-8-br-cyclic GMPS, 30 µM) inhibitors significantly reduced relaxations to tambulin in coronary artery rings without endothelium.

CONCLUSION

The present findings indicate that tambulin isolated from Z. armatum (fruits) is a major active principle inducing vasorelaxation through a direct effect at the vascular smooth muscle and involving both the cyclic AMP and/or cyclic GMP relaxing pathways.

Holistic Methods for the Analysis of cNMP Effects

Cyclic nucleotide monophosphates (cNMPs) typify the archetype second messenger in living cells and serve as molecular switches with broad functionality. cAMP and cGMP are the best-described cNMPs; however, there is a growing body of evidence indicating that also cCMP and cUMP play a substantial role in signal transduction. Despite research efforts, to date, relatively little is known about the biology of these noncanonical cNMPs, which is due, at least in part, to methodological issues in the past entailing setbacks of the entire field. Only recently, with the use of state-of-the-art techniques, it was possible to revive noncanonical cNMP research. While high-sensitive detection methods disclosed relevant levels of cCMP and cUMP in mammalian cells, knowledge about the biological effectors and their physiological interplay is still incomplete. Holistic biophysical readouts capture cell responses label-free and in an unbiased fashion with the advantage to detect concealed aspects of cell signaling that are arduous to access via traditional biochemical assay approaches. In this chapter, we introduce the dynamic mass redistribution (DMR) technology to explore cell signaling beyond established receptor-controlled mechanisms. Both common and distinctive features in the signaling structure of cCMP and cUMP were identified. Moreover, the integrated response of whole live cells revealed a hitherto undisclosed additional effector of the noncanonical cNMPs. Future studies will show how holistic methods will become integrated into the methodological arsenal of contemporary cNMP research.

Nobiletin, a citrus flavonoid, activates vasodilator-stimulated phosphoprotein in human platelets through non-cyclic nucleotide-related mechanisms

Nobiletin, a bioactive polymethoxylated flavone, has been described to possess a diversity of biological effects through its antioxidant and anti-inflammatory properties. Vasodilator-stimulated phosphoprotein (VASP) is a common substrate for cyclic AMP and cyclic GMP-regulated protein kinases [i.e., cyclic AMP-dependent protein kinase (PKA; also known as protein kinase A) and cyclic GMP-dependent protein kinase (PKG; also known as protein kinase G)] and it has been shown to be directly phosphorylated by protein kinase C (PKC). In the present study, we demonstrate that VASP is phosphorylated by nobiletin in human platelets via a non-cyclic nucleotide-related mechanism. This was confirmed by the use of inhibitors of adenylate cyclase (SQ22536) and guanylate cyclase [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ)], since they prevented VASP phosphorylation induced by nobiletin. Furthormore, this event was also not affected by specific inhibitors of PKA (H-89), PKG (KT5823) and PKC (Ro318220), representing cyclic nucleotide-dependent pathways upon nobiletin-induced VASP phosphorylation. Similarly, inhibitors of p38 mitogen-activated protein kinase (MAPK; SB203580), extracellular signal-regulated kinase 2 (ERK2; PD98059), c-Jun N-terminal kinase 1 (JNK1; SP600125), Akt (LY294002) and nuclear factor-κB (NF-κB; Bay11-7082) did not affect nobiletin-induced VASP phosphorylation. Moreover, electron spin resonance, dichlorofluorescein fluorescence and western blotting techniques revealed that nobiletin did not affect hydroxyl radicals (OH•), intracellular reactive oxygen species (ROS) and on protein carbonylation, respectively. Furthermore, the nobiletin-induced VASP phosphorylation was surprisingly reversed by the intracellular antioxidant, N-acetylcysteine (NAC), but not by the inhibitor of NADPH oxidase, diphenyleneiodonium chloride (DPI). It was surprising to observe the differential effects of nobiletin and NAC on VASP phosphorylation in human platelets, since they both have been reported to have antioxidant properties. The likely explanation for this discrepancy is that NAC may bind to allosteric sites on the receptor different from those that nobiletin binds to in human platelets. Taken together, our findings suggest that nobiletin induces VASP phosphorylation in human platelets through non-cyclic nucleotide-related mechanisms. Nevertheless, the exact mechanisms responsible for these effects need to be further confirmed in future studies.

Endothelium-independent vasorelaxant effect of a Berberis orthobotrys root extract via inhibition of phosphodiesterases in the porcine coronary artery

BACKGROUND

Berberis orthobotrys Bien ex Aitch. (Berberidaceae) is a plant indigenous of Pakistan that is locally used for the treatment of hypertension.

HYPOTHESIS

This study evaluated the vasoactive properties of a Berberis orthobotrys root extract and its fractions, and investigated the role of the endothelium and the underlying mechanism.

STUDY DESIGN

An aqueous methanolic extract of Berberis orthobotrys roots was prepared and submitted to a multi-step liquid-liquid fractionation with solvents of increasing polarity. Vascular reactivity of the different fractions was assessed using porcine coronary artery rings either with or without endothelium, and in the presence or absence of specific pharmacological tools. The ability of Berberis orthobotrys extracts to affect phosphodiesterase (PDE) activity was evaluated using a radioenzymatic method and purified phosphodiesterases.

RESULTS

The aqueous methanol extract induced similar relaxations in coronary artery rings with and without endothelium, and, amongst the three derived preparations, the butanol fraction (BFBO) was slightly but significantly more effective than the ethyl acetate fraction and the aqueous residue in rings without endothelium. Analysis of the butanol fraction (BFBO) by LC-ELSD-MS indicated the presence of four major isoquinoline alkaloids including berberine. BFBO significantly potentiated the relaxations induced by cyclic GMP- and cyclic AMP-dependent relaxing agonists, and inhibited contractions to KCl, CaCl2, and U46619 in endothelium denuded rings. In contrast, BFBO did not affect relaxations to endothelium-dependent vasodilators. BFBO concentration-dependently inhibited the cyclic GMP-hydrolyzing activity of basal PDE1, calmodulin-activated PDE1 and PDE5, and of cyclic AMP-hydrolyzing activity of PDE3 and PDE4 with IC50 values ranging from 40 to 130µg/ml.

CONCLUSION

The butanol fraction of the aqueous methanol extract of Berberis orthobotrys roots induced pronounced endothelium-independent relaxations and inhibited contractile responses by acting directly at the vascular smooth muscle in the coronary artery. Moreover, BFBO potentiated relaxations induced by both cyclic GMP- and cyclic AMP-dependent vasodilators most likely due to its ability to inhibit several vascular PDEs, and in particular PDE4 and PDE5.

Alteration of vascular reactivity in heart failure: role of phosphodiesterases 3 and 4

BACKGROUND AND PURPOSE

This study examined the role of the main vascular cAMP-hydrolysing phosphodiesterases (cAMP-PDE) in the regulation of basal vascular tone and relaxation of rat aorta mediated by β-adrenoceptors, following heart failure (HF).

EXPERIMENTAL APPROACH

Twenty-two weeks after proximal aortic stenosis, to induce HF, or SHAM surgery in rats, we evaluated the expression, activity and function of cAMP-PDE in the descending thoracic aorta.

KEY RESULTS

HF rat aortas exhibited signs of endothelial dysfunction, with alterations of the NO pathway, and alteration of PDE3 and PDE4 subtype expression, without changing total aortic cAMP-hydrolytic activity and PDE1, PDE3 and PDE4 activities. Vascular reactivity experiments using PDE inhibitors showed that PDE3 and PDE4 controlled the level of PGF2α -stimulated contraction in SHAM aorta. PDE3 function was partially inhibited by endothelial NO, whereas PDE4 function required a functional endothelium and was under the negative control of PDE3. In HF, PDE3 function was preserved, but its regulation by endothelial NO was altered. PDE4 function was abolished and restored by PDE3 inhibition. In PGF2α -precontracted arteries, β-adrenoceptor stimulation-induced relaxation in SHAM aorta, which was abolished in the absence of functional endothelium, as well as in HF aortas, but restored after PDE3 inhibition in all unresponsive arteries.

CONCLUSIONS AND IMPLICATIONS

Our study underlines the key role of the endothelium in controlling the contribution of smooth muscle PDE to contractile function. In HF, endothelial dysfunction had a major effect on PDE3 function and PDE3 inhibition restored a functional relaxation to β-adrenoceptor stimulation.

From canonical to non-canonical cyclic nucleotides as second messengers: pharmacological implications

This review summarizes our knowledge on the non-canonical cyclic nucleotides cCMP, cUMP, cIMP, cXMP and cTMP. We place the field into a historic context and discuss unresolved questions and future directions of research. We discuss the implications of non-canonical cyclic nucleotides for experimental and clinical pharmacology, focusing on bacterial infections, cardiovascular and neuropsychiatric disorders and reproduction medicine. The canonical cyclic purine nucleotides cAMP and cGMP fulfill the criteria of second messengers. (i) cAMP and cGMP are synthesized by specific generators, i.e. adenylyl and guanylyl cyclases, respectively. (ii) cAMP and cGMP activate specific effector proteins, e.g. protein kinases. (iii) cAMP and cGMP exert specific biological effects. (iv) The biological effects of cAMP and cGMP are terminated by phosphodiesterases and export. The effects of cAMP and cGMP are mimicked by (v) membrane-permeable cyclic nucleotide analogs and (vi) bacterial toxins. For decades, the existence and relevance of cCMP and cUMP have been controversial. Modern mass-spectrometric methods have unequivocally demonstrated the existence of cCMP and cUMP in mammalian cells. For both, cCMP and cUMP, the criteria for second messenger molecules are now fulfilled as well. There are specific patterns by which nucleotidyl cyclases generate cNMPs and how they are degraded and exported, resulting in unique cNMP signatures in biological systems. cNMP signaling systems, specifically at the level of soluble guanylyl cyclase, soluble adenylyl cyclase and ExoY from Pseudomonas aeruginosa are more promiscuous than previously appreciated. cUMP and cCMP are evolutionary new molecules, probably reflecting an adaption to signaling requirements in higher organisms.

cAMP signalling in the vasculature: the role of Epac (exchange protein directly activated by cAMP)

The second messenger cAMP plays a central role in mediating vascular smooth muscle relaxation in response to vasoactive transmitters and in strengthening endothelial cell-cell junctions that regulate the movement of solutes, cells and macromolecules between the blood and the surrounding tissue. The vasculature expresses three cAMP effector proteins: PKA (protein kinase A), CNG (cyclic-nucleotide-gated) ion channels, and the most recently discovered Epacs (exchange proteins directly activated by cAMP). Epacs are a family of GEFs (guanine-nucleotide-exchange factors) for the small Ras-related GTPases Rap1 and Rap2, and are being increasingly implicated as important mediators of cAMP signalling, both in their own right and in parallel with the prototypical cAMP target PKA. In the present paper, we review what is currently known about the role of Epac within blood vessels, particularly with regard to the regulation of vascular tone, endothelial barrier function and inflammation.

Exchange protein activated by cAMP (Epac) induces vascular relaxation by activating Ca2+-sensitive K+ channels in rat mesenteric artery

Vasodilator-induced elevation of intracellular cyclic AMP (cAMP) is a central mechanism governing arterial relaxation but is incompletely understood due to the diversity of cAMP effectors. Here we investigate the role of the novel cAMP effector exchange protein directly activated by cAMP (Epac) in mediating vasorelaxation in rat mesenteric arteries. In myography experiments, the Epac-selective cAMP analogue 8-pCPT-2-O-Me-cAMP-AM (5 μM, subsequently referred to as 8-pCPT-AM) elicited a 77.6 ± 7.1% relaxation of phenylephrine-contracted arteries over a 5 min period (mean ± SEM; n = 6). 8-pCPT-AM induced only a 16.7 ± 2.4% relaxation in arteries pre-contracted with high extracellular K(+) over the same time period (n = 10), suggesting that some of Epac's relaxant effect relies upon vascular cell hyperpolarization. This involves Ca(2+)-sensitive, large-conductance K(+) (BK(Ca)) channel opening as iberiotoxin (100 nM) significantly reduced the ability of 8-pCPT-AM to reverse phenylephrine-induced contraction (arteries relaxed by only 35.0 ± 8.5% over a 5 min exposure to 8-pCPT-AM, n = 5; P < 0.05). 8-pCPT-AM increased Ca(2+) spark frequency in Fluo-4-AM-loaded mesenteric myocytes from 0.045 ± 0.008 to 0.103 ± 0.022 sparks s(-1) μm(-1) (P < 0.05) and reversibly increased both the frequency (0.94 ± 0.25 to 2.30 ± 0.72 s(-1)) and amplitude (23.9 ± 3.3 to 35.8 ± 7.7 pA) of spontaneous transient outward currents (STOCs) recorded in isolated mesenteric myocytes (n = 7; P < 0.05). 8-pCPT-AM-activated STOCs were sensitive to iberiotoxin (100 nM) and to ryanodine (30 μM). Current clamp recordings of isolated myocytes showed a 7.9 ± 1.0 mV (n = 10) hyperpolarization in response to 8-pCPT-AM that was sensitive to iberiotoxin (n = 5). Endothelial disruption suppressed 8-pCPT-AM-mediated relaxation in phenylephrine-contracted arteries (24.8 ± 4.9% relaxation after 5 min of exposure, n = 5; P < 0.05), as did apamin and TRAM-34, blockers of Ca(2+)-sensitive, small- and intermediate-conductance K(+) (SK(Ca) and IK(Ca)) channels, respectively, and N(G)-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase (NOS). In Fluo-4-AM-loaded mesenteric endothelial cells, 8-pCPT-AM induced a sustained increase in global Ca(2+). Our data suggest that Epac hyperpolarizes smooth muscle by (1) increasing localized Ca(2+) release from ryanodine receptors (Ca(2+) sparks) to activate BK(Ca) channels, and (2) endothelial-dependent mechanisms involving the activation of SK(Ca)/IK(Ca) channels and NOS. Epac-mediated smooth muscle hyperpolarization will limit Ca(2+) entry via voltage-sensitive Ca(2+) channels and represents a novel mechanism of arterial relaxation.

Pentoxifylline reduces chronic post-ischaemia pain by alleviating microvascular dysfunction

BACKGROUND

Microvascular dysfunction and ischaemia in muscle play a role in the development of cutaneous tactile allodynia in chronic post-ischaemia pain (CPIP). Hence, studies were designed to assess whether pentoxifylline (PTX), a vasodilator and haemorrheologic agent, relieves allodynia in CPIP rats by alleviating microvascular dysfunction.

METHODS

Laser Doppler flowmetry of plantar blood flow was used to examine the effects of PTX on CPIP-induced alterations in post-occlusive reactive hyperaemia (reflecting microvascular dysfunction), and von Frey testing was used to examine its effects on CPIP-induced allodynia. Time-course effects of PTX on allodynia and microvascular dysfunction were assessed early (2-8 days) and late (18-25 days) post-ischaemia/reperfusion (I/R) injury, and its effects on allodynia were also tested at 30 days post-I/R injury.

RESULTS

PTX (25 mg/kg) produced significant anti-allodynic effects throughout the 21-day time course, but was not effective 30 days post-I/R injury. In laser Doppler studies, the reduced reactive hyperaemia in early CPIP rats was significantly improved by PTX (25 mg/kg). Conversely, treatment with PTX at the same dose did not affect reactive hyperaemia in late CPIP rats, likely since reactive hyperaemia was not significantly reduced pre-drug in these animals.

CONCLUSION

Since poor tissue perfusion underlies early stages of CPIP pain, the ameliorative effect of PTX on microvascular dysfunction might account for its anti-allodynic effect in our experimental model of complex regional pain syndrome type I.

Defective homocysteine metabolism: potential implications for skeletal muscle malfunction

Hyperhomocysteinemia (HHcy) is a systemic medical condition and has been attributed to multi-organ pathologies. Genetic, nutritional, hormonal, age and gender differences are involved in abnormal homocysteine (Hcy) metabolism that produces HHcy. Homocysteine is an intermediate for many key processes such as cellular methylation and cellular antioxidant potential and imbalances in Hcy production and/or catabolism impacts gene expression and cell signaling including GPCR signaling. Furthermore, HHcy might damage the vagus nerve and superior cervical ganglion and affects various GPCR functions; therefore it can impair both the parasympathetic and sympathetic regulation in the blood vessels of skeletal muscle and affect long-term muscle function. Understanding cellular targets of Hcy during HHcy in different contexts and its role either as a primary risk factor or as an aggravator of certain disease conditions would provide better interventions. In this review we have provided recent Hcy mediated mechanistic insights into different diseases and presented potential implications in the context of reduced muscle function and integrity. Overall, the impact of HHcy in various skeletal muscle malfunctions is underappreciated; future studies in this area will provide deeper insights and improve our understanding of the association between HHcy and diminished physical function.

Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments

Cyclic nucleotide phosphodiesterases (PDEs) that specifically inactivate the intracellular messengers cAMP and cGMP in a compartmentalized manner represent an important enzyme class constituted by 11 gene-related families of isozymes (PDE1 to PDE11). Downstream receptors, PDEs play a major role in controlling the signalosome at various levels of phosphorylations and protein/protein interactions. Due to the multiplicity of isozymes, their various intracellular regulations and their different cellular and subcellular distributions, PDEs represent interesting targets in intracellular pathways. Therefore, the investigation of PDE isozyme alterations related to various pathologies and the design of specific PDE inhibitors might lead to the development of new specific therapeutic strategies in numerous pathologies. This manuscript (i) overviews the different PDEs including their endogenous regulations and their specific inhibitors; (ii) analyses the intracellular implications of PDEs in regulating signalling cascades in pathogenesis, exemplified by two diseases affecting cell cycle and proliferation; and (iii) discusses perspectives for future therapeutic developments.

Cyclic nucleotide-dependent relaxation pathways in vascular smooth muscle

Vascular smooth muscle tone is controlled by a balance between the cellular signaling pathways that mediate the generation of force (vasoconstriction) and release of force (vasodilation). The initiation of force is associated with increases in intracellular calcium concentrations, activation of myosin light-chain kinase, increases in the phosphorylation of the regulatory myosin light chains, and actin-myosin crossbridge cycling. There are, however, several signaling pathways modulating Ca(2+) mobilization and Ca(2+) sensitivity of the contractile machinery that secondarily regulate the contractile response of vascular smooth muscle to receptor agonists. Among these regulatory mechanisms involved in the physiological regulation of vascular tone are the cyclic nucleotides (cAMP and cGMP), which are considered the main messengers that mediate vasodilation under physiological conditions. At least four distinct mechanisms are currently thought to be involved in the vasodilator effect of cyclic nucleotides and their dependent protein kinases: (1) the decrease in cytosolic calcium concentration ([Ca(2+)]c), (2) the hyperpolarization of the smooth muscle cell membrane potential, (3) the reduction in the sensitivity of the contractile machinery by decreasing the [Ca(2+)]c sensitivity of myosin light-chain phosphorylation, and (4) the reduction in the sensitivity of the contractile machinery by uncoupling contraction from myosin light-chain phosphorylation. This review focuses on each of these mechanisms involved in cyclic nucleotide-dependent relaxation of vascular smooth muscle under physiological conditions.

Oxidant sensing by protein kinases a and g enables integration of cell redox state with phosphoregulation

The control of vascular smooth muscle contractility enables regulation of blood pressure, which is paramount in physiological adaptation to environmental challenges. Maintenance of stable blood pressure is crucial for health as deregulation (caused by high or low blood pressure) leads to disease progression. Vasotone is principally controlled by the cyclic nucleotide dependent protein kinases A and G, which regulate intracellular calcium and contractile protein calcium sensitivity. The classical pathways for activation of these two kinases are well established and involve the formation and activation by specific cyclic nucleotide second messengers. Recently we reported that both PKA and PKG can be regulated independently of their respective cyclic nucleotides via a mechanism whereby the kinases sense cellular oxidant production using redox active thiols. This novel redox regulation of these kinases is potentially of physiological importance, and may synergise with the classical regulatory mechanisms.

Prostanoid TP receptor-mediated impairment of cyclic AMP-dependent vasorelaxation is reversed by phosphodiesterase inhibitors

Activation of the thromboxane prostanoid (TP) receptor produces potent vasoconstriction, which contributes to the increased vascular tone and blood pressure. The present study was designed to examine the hypothesis that stimulation of prostanoid TP receptors impairs endothelium-independent relaxations to cyclic AMP-elevating agents via increasing the activity of phosphodiesterases (PDEs). Rat carotid arteries without endothelium were isolated and suspended in myograph for the measurement of changes in isometric tension; the tissue content of cyclic AMP was assayed by enzyme immunoassay kit; and prostanoid TP receptor was detected in vascular wall by immunohistochemistry and Western blot. In phenylephrine-contracted rings without endothelium, relaxations induced by isoprenaline (receptor-mediated) and forskolin (receptor-independent) were markedly reduced by the presence of a prostanoid TP receptor agonist, U46619; the attenuated relaxations were prevented by acute treatment with S18886, the selective prostanoid TP receptor antagonist, but not by protein kinase C inhibitors. The reduced relaxations were partially restored by IBMX (non-selective PDE inhibitor), cilostazol (PDE3 inhibitor), rolipram (PDE4 inhibitor) or by Y27632 (Rho kinase inhibitor), but not by T0156 (PDE5 inhibitor). U46619 diminished isoprenaline- or forskolin-stimulated rise in cyclic AMP and this effect was inhibited by cilostazol, rolipram or Y27632. The present results suggest that activation of prostanoid TP receptors impairs cyclic AMP-dependent vasorelaxations partly via PDE- and RhoA/Rho kinase-dependent mechanisms. Inhibitors of PDEs and Rho kinase may be useful in the treatment of cardiovascular complications.

Forskolin Changes the Relationship between Cytosolic Ca and Contraction in Guinea Pig Ileum

This study was designed to clarify the mechanism of the inhibitory effect of forskolin on contraction, cytosolic Ca(2+) level ([Ca(2+)](i)), and Ca(2+) sensitivity in guinea pig ileum. Forskolin (0.1 nM~10 microM) inhibited high K(+) (25 mM and 40 mM)- or histamine (3 microM)-evoked contractions in a concentration-dependent manner. Histamine-evoked contractions were more sensitive to forskolin than high K(+)-evoked contractions. Spontaneous changes in [Ca(2+)](i) and contractions were inhibited by forskolin (1 microM) without changing the resting [Ca(2+)](i). Forskoln (10 microM) inhibited muscle tension more strongly than [Ca(2+)](i) stimulated by high K(+), and thus shifted the [Ca(2+)](i)-tension relationship to the lower-right. In histamine-stimulated contractions, forskolin (1 microM) inhibited both [Ca(2+)](i) and muscle tension without changing the [Ca(2+)](i)-tension relationship. In alpha-toxin-permeabilized tissues, forskolin (10 microM) inhibited the 0.3 microM Ca(2+)-evoked contractions in the presence of 0.1 mM GTP, but showed no effect on the Ca(2+)-tension relationship. We conclude that forskolin inhibits smooth muscle contractions by the following two mechanisms: a decrease in Ca(2+) sensitivity of contractile elements in high K(+)-stimulated muscle and a decrease in [Ca(2+)](i) in histamine-stimulated muscle.

Role of protein kinase G in nitric oxide deficiency-induced supersensitivity to nitrovasodilator in rat pulmonary artery

The aim of the present study was to examine the role of protein kinase G (G-kinase) in the mechanism of endogenous nitric oxide (NO) deficiency-induced supersensitivity to the nitrovasodilator sodium nitroprusside (SNP) in isolated rat pulmonary artery. Tension experiments and cGMP measurements were carried out on isolated rat pulmonary artery to assess the influence of NO deficiency, caused by either N-nitro-L-arginine methyl ester (L-NAME) treatment or endothelium removal on the vasodilator potency of SNP. Sodium nitroprusside was more potent (pD2; 8.21 +/- 0.04) in relaxing arterial rings treated with 100microM L-NAME or denuded of the endothelium (pD2; 8.44 +/- 0.11) compared with the endothelium-intact controls (pD2; 7.61 +/- 0.05). Similarly, the tissue sensitivity to 8-Br-cGMP, a G-kinase activator, was significantly (P < 0.05) greater after L-NAME treatment (pD2; 5.04 +/- 0.09) or endothelium removal (pD2; 5.28 +/- 0.11) in comparison with the controls (pD2; 4.22 +/- 0.17). On the other hand, dibutyryl cAMP, an activator of protein kinase A, was equipotent in dilating control (pD2; 4.14 +/- 0.04) and L-NAME-treated (pD2 4.21 +/- 0.05) vessels. Further, L-NAME treatment significantly (P < 0.05) decreased the basal cGMP but enhanced SNP (1 microM)-stimulated increase in the tissue cyclic nucleotide levels (271.8 +/- 39.93 pmol/mg protein versus control: 66.19 +/- 7.18 pmol/mg protein), indicating sensitization of soluble guanylyl cyclase to NO. The increased sensitivity of G-kinase to cGMP observed in the present study suggests a novel mechanism of supersensitivity in vascular smooth muscle to nitrovasodilators in acute NO deficiency. Further, it explains the influence of ambient cGMP in determining the sensitivity of G-kinase in vascular smooth muscle.

Adrenomedullin-induced relaxation of rat brain pericytes is related to the reduced phosphorylation of myosin light chain through the cAMP/PKA signaling pathway

Brain pericytes are known to embrace the abluminal endothelial surfaces of cerebral microvessels. The rich expression of contractile proteins in these cells suggests pericytal regulation of cerebral blood flow. Here, we investigated the molecular mechanisms by which an endothelium-derived relaxing factor, adrenomedullin, was able to induce the relaxation of rat primary cultured brain pericytes. Adrenomedullin increased the relative proportion of pericytes that were relaxed, as shown by an increased cell surface area. A smaller fragment of adrenomedullin (adrenomedullin(22-52)) blocked the adrenomedullin-induced relaxation. Adrenomedullin increased intracellular cAMP concentrations and decreased the phosphorylation of myosin light chain (MLC). H89 (a PKA inhibitor) inhibited the adrenomedullin-induced increase in the number of relaxed pericytes, and returned the level of phosphorylation of MLC to the control level. The results of the present study suggest that adrenomedullin-induced relaxation of brain pericytes is related to the reduced phosphorylation of MLC through cAMP/PKA.

Phosphodiesterase type 5: expanding roles in cardiovascular regulation

Phosphodiesterase type 5A (PDE5A) selectively hydrolyzes cyclic GMP. Inhibitors of PDE5A such as sildenafil are widely used to treat erectile dysfunction, but growing evidence supports important roles for the enzyme in both the vasculature and heart. In disorders such as cardiac failure, PDE5A upregulation may contribute to a decline in cGMP and protein kinase G signaling, exacerbating dysfunction. PDE5A plays an important role in the pulmonary vasculature where its inhibition benefits patients with pulmonary hypertension. In the heart, PDE5A signaling appears compartmentalized, and its inhibition is cardioprotective against ischemia-reperfusion and antracycline toxicity, blunts acute adrenergic contractile stimulation, and can suppress chronic hypertrophy and dysfunction attributable to pressure-overload. In this review, we discuss the molecular biology, pharmacology, and physiology of PDE5A, mechanisms of vascular and cardiac regulation, and recent evidence supporting the utility of selective PDE5A inhibition for the treatment of cardiovascular disorders.

Non-genomic vascular actions of female sex hormones: physiological implications and signalling pathways

1. Epidemiological studies indicate a lower incidence of coronary heart disease in premenopausal women compared with age-matched men and post-menopausal women. Accumulating evidence suggests that this cardiovascular protection observed in premenopausal women is at least partially attributed to the direct action of oestrogens on the vascular system. 2. Research focused on vascular actions of 17beta-oestradiol indicates that this female sex hormone favourably modulates vascular reactivity at physiological concentrations. The vascular actions of 17beta-oestradiol appear independent of its genomic actions. Both endothelium-dependent and -independent signalling cascades have been implicated in the vascular effects of 17beta-oestradiol. 3. However, clinical trials on hormone-replacement therapy argue against a role of oestrogens in preventing the development of coronary heart disease. Supplementation with oestrogen is also complicated with the increased risk of breast and endometrial cancer. Hence, a better understanding of the vascular actions of 17beta-oestradiol will serve to enhance our understanding of its role in coronary heart disease.

Endogenous nitric oxide attenuates beta-adrenoceptor-mediated relaxation in rat aorta

1. Divergent evidence suggests that the intracellular signalling pathways for beta-adrenoceptor-mediated vascular relaxation involves either cAMP/protein kinase (PK) A or endothelial nitric oxide (NO) release and subsequent activation of cGMP/PKG. The present study identifies the relative roles of NO and cAMP, as well as dependence on the endothelium for beta-adrenoceptor-mediated relaxation of rat isolated aortas. 2. Cumulative concentration-response curves to isoprenaline (0.01-3 micromol/L) in phenylephrine (0.1 micromol/L)-preconstricted endothelium-intact and -denuded aortas were constructed. Isoprenaline-mediated relaxation was partially reduced by endothelium removal and the presence of the NO synthase inhibitor N(G)-monomethyl-L-arginine (0.1 mmol/L), but not by the cAMP antagonist (Rp)-cyclic adenosine-3',5'-monophosphorothioate (Rp-cAMPS; 0.5 mmol/L). 3. In contrast, in endothelium-denuded aortas, the isoprenaline-mediated relaxation was inhibited by Rp-cAMPS and this inhibition was lost in the presence of the NO donor sodium nitroprusside (1 nmol/L). This effect was not due to phosphodiesterase (PDE) activity because the non-selective PDE inhibitor 3-isobutyl-1-methylxanthine (1 micromol/L) failed to affect the isoprenaline vasorelaxant response. 4. The K(+) channel blocker tetraethylammonium (TEA; 1 mmol/L) attenuated isoprenaline-induced relaxation in endothelium-denuded aorta, but its effect was non-additive with Rp-cAMPS, suggesting that the K(+) channel component may involve cAMP. In endothelium-intact aortas, TEA but not Rp-cAMPS reduced isoprenaline relaxation, suggesting an additional non-cAMP component. 5. These findings suggest that beta-adrenoceptors induce vascular smooth muscle relaxation by acting through the NO-cGMP pathway and, when that is disrupted by endothelium removal or the presence of an NO synthase inhibitor, the cAMP pathway in smooth muscles is used. The lack of cAMP participation in endothelium-intact vessels may be because NO suppresses or overrides the cAMP effect.

Study of the mechanisms involved in the vasorelaxation induced by (-)-epigallocatechin-3-gallate in rat aorta

This study investigated several mechanisms involved in the vasorelaxant effects of (-)-epigallocatechin-3-gallate (EGCG). EGCG (1 microM-1 mM) concentration dependently relaxed, after a transient increase in tension, contractions induced by noradrenaline (NA, 1 microM), high extracellular KCl (60 mM), or phorbol 12-myristate 13-acetate (PMA, 1 microM) in intact rat aortic rings. In a Ca2+ -free solution, EGCG (1 microM-1 mM) relaxed 1 microM PMA-induced contractions, without previous transient contraction. However, EGCG (1 microM-1 mM) did not affect the 1 microM okadaic acid-induced contractions. Removal of endothelium and/or pretreatment with glibenclamide (10 microM), tetraethylammonium (2 mM) or charybdotoxin (100 nM) plus apamin (500 nM) did not modify the vasorelaxant effects of EGCG. In addition, EGCG noncompetitively antagonized the contractions induced by NA (in 1.5 mM Ca2+ -containing solution) and Ca2+ (in depolarizing Ca2+ -free high KCl 60 mM solution). In rat aortic smooth muscle cells (RASMC), EGCG (100 microM) reduced increases in cytosolic free Ca2+ concentration ([Ca2+]i) induced by angiotensin II (ANG II, 100 nM) and KCl (60 mM) in 1.5 mM CaCl2 -containing solution and by ANG II (100 nM) in the absence of extracellular Ca2+. In RASMC, EGCG (100 microM) did not modify basal generation of cAMP or cGMP, but significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cAMP and cGMP production. EGCG inhibited the enzymatic activity of all the cyclic nucleotide PDE isoenzymes present in vascular tissue, being more effective on PDE2 (IC50 approximately 17) and on PDE1 (IC50 approximately 25). Our results suggest that the vasorelaxant effects of EGCG in rat aorta are mediated, at least in part, by an inhibition of PDE activity, and the subsequent increase in cyclic nucleotide levels in RASMC, which, in turn, can reduce agonist- or high KCl concentration-induced increases in [Ca2+]i.

Cyclic nucleotide signaling in cavernous smooth muscle

INTRODUCTION

Penile erection depends on cavernous smooth muscle relaxation that is principally regulated by cyclic nucleotide signaling. It is hoped that a comprehensive review of publications relevant to this subject will be helpful to both scientists and clinicians who are interested in the sciences of erectile function/dysfunction. AIMS. To review the roles of extracellular signaling molecules, their receptors, intracellular effectors, and phosphodiesterases in cyclic nucleotide signaling that leads to cavernous smooth muscle relaxation. The involvement of these molecules in the development of erectile dysfunction and the possibility of using them as therapeutic agents or targets are also discussed.

METHODS

Entrez, the search engine for life sciences, was used to search for publications relevant to the topics of this review. Keywords used in the searches included vascular, cavernous, penis, smooth muscle, signaling molecules (adenosine, nitric oxide, etc.), and key elements in the cyclic nucleotide signaling pathways (cAMP, cGMP, cyclases, PKG, PKA, etc.). Articles that are dedicated to the study of erectile function/dysfunction were prioritized for citation.

RESULTS

More than 1,000 articles were identified, many of which are studies of the vascular system and are therefore reviewed but not cited. Studies on erectile function have identified both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways in cavernous smooth muscle. Many signaling molecules of these two pathways have been shown capable of inducing erection when administered intracavernously. However, for sexually induced erection, nitric oxide (NO) is the responsible signaling molecule and it passes on the signal through soluble guanyl cyclase (sGC), cGMP, and protein kinase G (PKG).

CONCLUSIONS

The NO/sGC/cGMP/PKG pathway is principally responsible for sexually stimulated erection. Detumescence is mainly carried out by the degradation of cGMP by phosphodiesterase 5. Both cAMP and cGMP signaling pathways are susceptible to genetic and biochemical alterations in association with erectile dysfunction. Several key elements along these pathways are potential therapeutic targets.

Functional interaction of a beta-adrenergic agonist and cyclic GMP phosphodiesterase inhibitor in control and hypertrophic cardiomyocytes

This study tested the hypothesis that the positive inotropic effect of beta-adrenoceptor stimulation would be inhibited by increases in cyclic GMP in control cardiomyocytes and that this response would be modified in hypertrophic cardiomyocytes. Cell functional data as well as GMP and cyclic AMP data were collected from 7 control and 7 1K1C (one-kidney-one-clip) renal hypertensive hypertrophic rabbits. Using isolated control and IKIC ventricular myocytes, data were obtained at baseline and after treatment with the beta-adrenoceptor agonist isoproterenol (10(-8, -6) mol/l) or the cyclic GMP-phosphodiesterase inhibitor zaprinast (10(-5) mol/l) followed by isoproterenol (10(-8, -6) mol/l). We found that in control rabbits, isoproterenol (10(-6) mol/l) increased percent shortening (4.8 +/- 0.2 to 6.4 +/- 0.3%) and cyclic AMP (2.3 +/- 0.3 to 5.0 +/- 0.7 pmol/10(5) cells). Zaprinast 10(-5) mol/l increased cyclic GMP (150 +/- 20 to 209 +/- 14 fmol/10(5) cells) and decreased percent shortening (6.2 +/- 0.4 to 5.2 +/- 0.3). Zaprinast 10(-5) mol/l prevented the functional response to isoproterenol in control (5.2 +/- 0.3 to 4.7 +/- 0.3), without changing cyclic AMP levels. In 1K1C rabbits, isoproterenol (10(-6) mol/l) increased cyclic AMP (4.9 +/- 0.8 to 7.6 +/- 1.4 pmol/10(5) cells) without changing function. Zaprinast 10(-5) mol/l increased cyclic GMP (182 +/- 23 to 233 +/- 24 fmol/10(5) cells) and decreased percent shortening (6.6 +/- 0.9 to 4.7 +/- 0.5), but did not alter the lack of effect of isoproterenol in 1K1C. In control cardiomyocytes, cyclic GMP blunted the isoproterenol contraction response without changing cyclic AMP levels, but isoproterenol's functional effect was not seen in 1K1C cardiomyocytes.

Cyclic nucleotide phosphodiesterase (PDE) superfamily: a new target for the development of specific therapeutic agents

Cyclic nucleotide phosphodiesterases (PDEs), which are ubiquitously distributed in mammalian tissues, play a major role in cell signaling by hydrolyzing cAMP and cGMP. Due to their diversity, which allows specific distribution at cellular and subcellular levels, PDEs can selectively regulate various cellular functions. Their critical role in intracellular signaling has recently designated them as new therapeutic targets for inflammation. The PDE superfamily represents 11 gene families (PDE1 to PDE11). Each family encompasses 1 to 4 distinct genes, to give more than 20 genes in mammals encoding the more than 50 different PDE proteins probably produced in mammalian cells. Although PDE1 to PDE6 were the first well-characterized isoforms because of their predominance in various tissues and cells, their specific contribution to tissue function and their regulation in pathophysiology remain open research fields. This concerns particularly the newly discovered families, PDE7 to PDE11, for which roles are not yet established. In many pathologies, such as inflammation, neurodegeneration, and cancer, alterations in intracellular signaling related to PDE deregulation may explain the difficulties observed in the prevention and treatment of these pathologies. By inhibiting specifically the up-regulated PDE isozyme(s) with newly synthesized potent and isozyme-selective PDE inhibitors, it may be potentially possible to restore normal intracellular signaling selectively, providing therapy with reduced adverse effects.

Activation of alpha2-adrenoceptors is necessary to induce nitric oxide release in isoprenaline-induced relaxation

The aim of this study was to investigate the role of the contractile agent on the relaxation induced by isoprenaline and the contribution of nitric oxide (NO) and cGMP to this relaxation. These studies were conducted in intact endothelium or denuded aortas contracted with the EC50 of norepinephrine (NE) or phenylephrine (Phe), and the relaxation induced by isoprenaline (non-selective beta-adrenoceptor agonist) or forskolin (activator of adenylyl-cyclase) was studied. The maximum effect (Emax) and pD2 were analysed. Isoprenaline and forskolin-induced relaxation were not changed by the endothelium removal in both NE and Phe-contracted aortas. However, L-NAME reduced the relaxation induced by isoprenaline (Emax from 94.48+/-2.30%, n=7 to 66.17+/-11.73%, n=7; pD2 from 7.56+/-0.10 to 6.08+/-0.15) only in NE-contracted aortas. The pD2 of isoprenaline was also reduced by ODQ (6.57+/-0.13), but not the Emax. The inhibitory effects of L-NAME and ODQ were reversed by yohimbine. L-NAME, ODQ and oxyhemoglobin had no effect on the relaxation induced by isoprenaline in Phe-contracted aortas. Taken together, these results suggest that norepinephrine, a non-selective alpha-adrenoceptor agonist can also activate alpha2-adrenoceptors sensitive to yohimbine in the endothelial cells, activating the NO-synthase and cGMP production which would potentiate the relaxation induced by isoprenaline. However, this pathway is not activated with Phe, the selective alpha1-adrenoceptors agonist.

Cyclic GMP protein kinase activity is reduced in thyroxine-induced hypertrophic cardiac myocytes

1. We tested the hypothesis that the cGMP-dependent protein kinase has major negative functional effects in cardiac myocytes and that the importance of this pathway is reduced in thyroxine (T4; 0.5 mg/kg per day for 16 days) hypertrophic myocytes. 2. Using isolated ventricular myocytes from control (n = 7) and T4-treated (n = 9) rabbit hypertrophic hearts, myocyte shortening was studied with a video edge detector. Oxygen consumption was measured using O2 electrodes. Protein phosphorylation was measured autoradiographically. 3. Data were collected following treatment with: (i) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT; 10-7 or 10-5 mol/L); (ii) 8-bromo-cAMP (10-5 mol/L) followed by PCPT; (iii) beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP; 10-7 or 10-5 mol/L); or (iv) 8-bromo-cAMP (10-5 mol/L) followed by SP. 4. There were no significant differences between groups in baseline percentage shortening (Pcs; 4.9 +/- 0.2 vs 5.6 +/- 0.4% for control and T4 groups, respectively) and maximal rate of shortening (Rs; 64.8 +/- 5.9 vs 79.9 +/- 7.1 micro m/ s for control and T4 groups, respectively). Both SP and PCPT decreased Pcs (-43 vs-21% for control and T4 groups, respectively) and Rs (-36 vs-22% for control and T4 groups, respectively), but the effect was significantly reduced in T4 myocytes. 8-Bromo-cAMP similarly increased Pcs (28 vs 23% for control and T4 groups, respectively) and Rs (20 vs 19% for control and T4 groups, respectively). After 8-bromo-cAMP, SP and PCPT decreased Pcs (-34%) and Rs (-29%) less in the control group. However, the effects of these drugs were not altered in T4 myocytes (Pcs -24%; Rs -22%). Both PCPT and cAMP phosphorylated the same five protein bands. In T4 myocytes, these five bands were enhanced less. 5. We conclude that, in control ventricular myocytes, the cGMP-dependent protein kinase exerted major negative functional effects but, in T4-induced hypertrophic myocytes, the importance of this pathway was reduced and the interaction between cAMP and the cGMP protein kinase was diminished.

Comparative study of the vasorelaxant activity, superoxide-scavenging ability and cyclic nucleotide phosphodiesterase-inhibitory effects of hesperetin and hesperidin

This study investigated the vasorelaxant activity, superoxide radicals (O2(*-))-scavenging capacity and cyclic nucleotide phosphodiesterase (PDE)-inhibitory effects of hesperidin and hesperetin, two flavonoids mainly isolated from citrus fruits. Hesperetin concentration-dependently relaxed the isometric contractions induced by noradrenaline (NA, 1 microM) or by a high extracellular KCl concentration (60 mM) in intact rat isolated thoracic aorta rings. However, hesperetin (10 microM-0.3 mM) did not affect the contractile response induced by okadaic acid (OA, 1 microM). Mechanical removal of endothelium and/or pretreatment of aorta rings with glibenclamide (GB, 10 microM), tetraethylammonium (TEA, 2 mM) or nifedipine (0.1 microM) did not significantly modify the vasorelaxant effects of this flavonoid. Hesperetin (10 microM-0.1 mM) did not affect the basal uptake of (45)Ca(2+) but decreased the influx of (45)Ca(2+) induced by NA and KCl in endothelium-containing and endothelium-denuded rat aorta. Hesperetin (10 microM-0.1 mM) did not scavenge O2(*-) generated by the phenazine methosulfate (PMS)-reduced beta-nicotinamide adenine dinucleotide (NADH) system. Hesperetin (0.1 mM) significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cyclic nucleotide (cAMP and cGMP) production in cultured rat aortic myocytes. Hesperetin preferentially inhibited calmodulin (CaM)-activated PDE1 and PDE4 isolated from bovine aorta with IC(50) values of about 74 microM and 70 microM respectively. In contrast, the 7-rhamnoglucoside of hesperetin, hesperidin (10 microM-0.1 mM), was inactive in practically all experiments, although it inhibited basal and cGMP-activated PDE2 isolated from platelets (IC(50) values of 32+/-4 microM and 137+/-34 microM respectively). These results suggest that the vasorelaxant effects of hesperetin are basically due to the inhibition of PDE1 and PDE4 activities.

Negative feedback exerted by cAMP-dependent protein kinase and cAMP phosphodiesterase on subsarcolemmal cAMP signals in intact cardiac myocytes: an in vivo study using adenovirus-mediated expression of CNG channels

Intracardiac cAMP levels are modulated by hormones and neuromediators with specific effects on contractility and metabolism. To understand how the same second messenger conveys different information, mutants of the rat olfactory cyclic nucleotide-gated (CNG) channel alpha-subunit CNGA2, encoded into adenoviruses, were used to monitor cAMP in adult rat ventricular myocytes. CNGA2 was not found in native myocytes but was strongly expressed in infected cells. In whole cell patch-clamp experiments, the forskolin analogue L-858051 (L-85) elicited a non-selective, Mg2+ -sensitive current observed only in infected cells, which was thus identified as the CNG current (ICNG). The beta-adrenergic agonist isoprenaline (ISO) also activated ICNG, although the maximal efficiency was approximately 5 times lower than with L-85. However, ISO and L-85 exerted a similar maximal increase of the L-type Ca2+ current. The use of a CNGA2 mutant with a higher sensitivity for cAMP indicated that this difference is caused by the activation of a localized fraction of CNG channels by ISO. cAMP-dependent protein kinase (PKA) blockade with H89 or PKI, or phosphodiesterase (PDE) inhibition with IBMX, dramatically potentiated ISO- and L-85-stimulated ICNG. A similar potentiation of beta-adrenergic stimulation occurred when PDE4 was blocked, whereas PDE3 inhibition had a smaller effect (by 2-fold). ISO and L-85 increased total PDE3 and PDE4 activities in cardiomyocytes, although this effect was insensitive to H89. However, in the presence of IBMX, H89 had no effect on ISO stimulation of ICNG. This study demonstrates that subsarcolemmal cAMP levels are dynamically regulated by a negative feedback involving PKA stimulation of subsarcolemmal cAMP-PDE.

Diabetes-related changes in cAMP-dependent protein kinase activity and decrease in relaxation response in rat mesenteric artery

Using superior mesenteric artery rings isolated from age-matched controls and streptozotocin (STZ)-induced diabetic rats, we recently demonstrated that EDHF-type relaxation is impaired in STZ-induced diabetic rats, possibly due to a reduced action of cAMP via increased phosphodiesterase (PDE) activity (Matsumoto T, Kobayashi T, and Kamata K. Am J Physiol Heart Circ Physiol 285: H283-H291, 2003). Here, we investigated the activity and expression of cAMP-dependent protein kinase (PKA), an enzyme that is produced by a pleiotropic and plays key roles in the transduction of many external signals through the cAMP second messenger pathway and in cAMP-mediated vasorelaxation. The relaxation induced by cilostamide, a selective PDE3 inhibitor, was significantly weaker in superior mesenteric artery rings from STZ-induced diabetic rats than in those from age-matched controls. The relaxation responses to 8-bromo-cAMP (8Br-cAMP) and N6,O2-dibutyryl-adenosine-cAMP (db-cAMP), a cell-permeant cAMP analog, were also impaired in the STZ diabetic group. PKA activity in the db-cAMP-treated mesenteric artery was significantly lower in the STZ diabetic group. The expression levels of the mRNA and protein for PKA catalytic subunit Cat-alpha were significantly decreased in the STZ diabetic group, but those for PKA regulatory subunit isoform RII-beta were increased. We conclude that the abnormal vascular relaxation responsiveness seen in STZ-induced diabetic rats may be attributable not only to increased PDE activity but also to decreased PKA activity. Possibly, the decreased PKA activity may result from an imbalance between PKA catalytic and regulatory subunit expressions.

Changes in the vascular beta-adrenoceptor-activated signalling pathway in 2Kidney-1Clip hypertensive rats

1. beta-Adrenoceptor (beta-AR)-mediated vasodilation, which plays an important physiological role in the regulation of vascular tone, is decreased in two-kidney, one clip (2K-1C) renal hypertension. In this study, downstream pathways related to vascular beta-AR activation were evaluated in 2K-1C rats. 2. Relaxation responses to isoprenaline, forskolin and 8-Br-cAMP were diminished in aortas without endothelium from 2K-1C when compared to those in normotensive two kidney (2K). Basal adenosine-3',5'-monophosphate (cAMP), as well as isoprenaline-induced increase in cAMP levels, was not different between 2K and 2K-1C aortas. 3. Contractile responses to caffeine, after depletion and reloading of intracellular Ca(2+) stores, were greater in 2K-1C than in 2K. The presence of isoprenaline during the Ca(2+)-reloading period abolished the differences between groups by increasing caffeine contraction in 2K without changing this response in 2K-1C aortas. Inhibition of the sarcolemmal Ca(2+)ATPase with thapsigargin markedly attenuated isoprenaline vasodilation in both 2K and 2K-1C and abolished the differences between groups. 4. Blockade of ATP-sensitive K(+) channels (K(ATP)) channels with glibenclamide significantly decreased isoprenaline vasodilation in 2K-1C without affecting this response in 2K. Both vascular gene and protein expression of protein kinase A (PKA), as well as phosphoserine-containing proteins, were increased in 2K-1C vs 2K rats. 5. In conclusion, decreased isoprenaline vasodilation in 2K-1C hypertensive rats is related to impaired modulation of the sarcolemmal Ca(2+)ATPase activity. Moreover, K(ATP) channels may play a compensatory role on isoprenaline-induced relaxation in renal hypertension. Both Ca(2+)ATPase and K(ATP) channel functional alterations, associated with decreased beta-AR vasodilation, are paralleled by an upregulation of protein kinase A (PKA) and phosphoserine proteins expression.

The Roles of Cyclic Adenosine Monophosphate- and Cyclic Guanosine Monophosphate-Dependent Protein Kinase Pathways in Hydrogen Peroxide-Induced Contractility of Microvascular Lung Pericytes

BACKGROUND

Sepsis and posttraumatic inflammatory processes are accompanied by definite changes in microvascular permeability, particularly in the lung. These permeability changes may occur because of damaged regulatory mechanisms at the level of the capillary wall. Pericytes are adventitial cells located within the basement membrane of capillaries. These cells contain multiple cytoplasmic processes that envelope endothelial cells, and are consequently thought to stabilize capillary walls and participate in microcirculation and endothelial cell permeability. Data from this laboratory and other laboratories have confirmed that pericytes are contractile cells, adding to the evidence that pericytes may influence or help regulate capillary permeability. We have already determined that hydrogen peroxide (H2O2) causes dose-dependent relaxation in microvascular lung pericytes (MLPs) at 10 minutes and, conversely, dose-dependent contraction at 30 minutes. It is the aim of this study to determine the mechanism of this biphasic contractile response. Specifically, we will determine whether cyclic adenosine monophosphate (cAMP)- or cyclic guanosine monophosphate (cGMP)-dependent protein kinase intracellular pathways are responsible for the hydrogen peroxide-induced contractility of MLPs.

METHODS

Rat MLPs were isolated by previously published protocol and cultured on collagen gel matrices. MLPs were pretreated with either ODQ, a soluble guanylate cyclase inhibitor (100 mumol/L), for 15 minutes; GKIP, a protein kinase G inhibitor (100 mumol/L), for 1 hour; SQ22536, an adenylate cyclase inhibitor (100 mumol/L), for 15 minutes; or H89, a protein kinase A inhibitor (10 mumol/L), for 1 hour. Hydrogen peroxide was then introduced to each MLP culture at 10 mumol/L, 100 mumol/L, and 1 mmol/L. After each of these treatments, the surface area of the collagen gels was digitally quantified at 10 and 30 minutes.

RESULTS

SQ22536 attenuated both relaxation at 10 minutes and the contraction seen at 30 minutes for all concentrations of H2O2. H89 caused a marked basal relaxation and prevented the cells from contracting at 30-minute exposures to all concentrations of H2O2. Both ODQ and GKIP attenuated the relaxation at 10 minutes but had no affect on the later contraction.

CONCLUSION

The cGMP-dependent protein kinase pathway is a mechanism for H2O2-induced relaxation of MLPs. Up-regulation of cAMP and cGMP is responsible for early H2O2-induced relaxation and late contraction. Protein kinase A (cAMP-dependent protein kinase pathway) may be an important intracellular signaling protein in the H2O2-induced contraction of MLPs or may be unable to down-regulate cAMP once inhibited. This evidence further supports the concept that there are separate intracellular pathways that regulate divergent cellular responses. This idea parallels the clinical concept of reversible and irreversible dysfunction of cellular processes in shock, and that the cellular dysfunction is initiated by separate intracellular pathways.

Effect of cilostazol on impaired vasodilatory response of the brachial artery to ischemia in smokers

The vascular endothelial function of smokers is known to be impaired. This study investigated whether cilostazol could improve the vasodilatory response of the brachial artery to ischemia, an indicator of endothelial function, in ten male smokers. Endothelium-dependent vasodilatation and endothelium-independent vasodilatation of the brachial artery were measured in 11 male non-smokers and 20 male smokers with matching age and weight. The results showed that the vasodilatory response to reactive hyperemia was significantly smaller in the smokers (4.8 +/- 1.6%) when compared to that in the non-smokers (7.6 +/- 2.5%) (p = 0.0013). However, no significant difference in the vasodilatory response to isosorbide dinitrate was observed between the two groups. In addition, there were no significant differences in serum lipid, Lp (a), or blood homocysteine between the smokers and non-smokers. When 150 mg/day of cilostazol was administered for two weeks, the vasodilatory response to reactive hyperemia significantly improved (4.2 +/- 1.2% to 7.8 +/- 3.5%, p = 0.0032). The increased vasodilatory response to reactive hyperemia by cilostazol was reduced after cessation of the drug (4.5 +/- 1.5%). These findings suggest that cilostazol improves vascular endothelial dysfunction in smokers.

Role of cyclic nucleotide phosphodiesterase isoforms in cAMP compartmentation following beta2-adrenergic stimulation of ICa,L in frog ventricular myocytes

The role of cyclic nucleotide phosphodiesterase (PDE) isoforms in the beta2-adrenergic stimulation of the L-type Ca2+ current (ICa,L) was investigated in frog ventricular myocytes using double patch-clamp and double-barrelled microperfusion techniques. Isoprenaline (ISO, 1 nM to 10 microM) was applied on one half of the cell, either alone or in the presence of PDE inhibitors, and the local and distant responses of ICa,L were used to determine the gradient of local vs. distant cAMP concentration (alpha). IBMX (100 microM), a non-selective PDE inhibitor, reduced alpha from 40 to 4.4 indicating a 9-fold reduction in intracellular cAMP compartmentation when all PDE activity was blocked. While PDE1 and PDE2 inhibition had no effect, PDE3 inhibition by milrinone (3 microM) or PDE4 inhibition by Ro 20-1724 (3 microM) reduced alpha by 6- and 4-fold, respectively. A simultaneous application of milrinone and Ro 20-1724 produced a similar effect to IBMX, showing that PDE3 and PDE4 were the major PDEs accounting for cAMP compartmentation. Okadaic acid (3 microM), a non-selective phosphatase inhibitor, or H89 (1 microM), an inhibitor of cAMP-dependent protein kinase (PKA), had no effect on the distant response of ICa,L to ISO indicating that PDE activation by PKA played a minor role in cAMP compartmentation. Our results demonstrate that PDE activity determines the degree of cAMP compartmentation in frog ventricular cells upon beta2-adrenergic stimulation. PDE3 and PDE4 subtypes play a major role in this process, and contribute equally to ensure a functional coupling of beta2-adrenergic receptors with nearby Ca2+ channels via local elevations of cAMP.

Cyclic AMP compartmentation due to increased cAMP-phosphodiesterase activity in transgenic mice with a cardiac-directed expression of the human adenylyl cyclase type 8 (AC8)

Hearts from AC8TG mice develop a higher contractility (LVSP) and larger Ca2+ transients than NTG mice, with (surprisingly) no modification in L-type Ca2+ channel current (ICa,L) (1). In this study, we examined the cardiac response of AC8TG mice to beta-adrenergic and muscarinic agonists and IBMX, a cyclic nucleotide phosphodiesterase (PDE) inhibitor. Stimulation of LVSP and ICa,L by isoprenaline (ISO, 100 nM) was twofold smaller in AC8TG vs. NTG mice. In contrast, IBMX (100 microM) produced a twofold higher stimulation of ICa,L in AC8TG vs. NTG mice. IBMX (10 microM) increased LVSP by 40% in both types of mice, but contraction and relaxation were hastened in AC8TG mice only. Carbachol (10 microM) had no effect on basal contractility in NTG hearts but decreased LVSP by 50% in AC8TG mice. PDE assays demonstrated an increase in cAMP-PDE activity in AC8TG hearts, mainly due to an increase in the hydrolytic activity of PDE4 and PDE1 toward cAMP and a decrease in the activity of PDE1 and PDE2 toward cGMP. We conclude that cardiac expression of AC8 is accompanied by a rearrangement of PDE isoforms, leading to a strong compartmentation of the cAMP signal that shields L-type Ca2+ channels and protects the cardiomyocytes from Ca2+ overload.

Influence of the nature of pre-contraction on the responses to commonly employed vasodilator agents in rat-isolated aortic rings

The relaxing properties of vasodilator drugs in vitro may depend on the characteristics of the contractile state of the vessel investigated. Rat-isolated thoracic aortas were exposed to different types of pre-contraction. The following vasoconstrictor agents were used: phenylephrine (PhE), a selective alpha1-adrenoceptor agonist; St 587, a partial alpha1-adrenoceptor stimulant; U46619 (U-46). a thromboxane A2 agonist: and potassium ions causing receptor-independent depolarization of the membrane. After pre-contraction, various differential vasodilator drugs were investigated: methacholine (MCh, endothelium dependent), sodium nitroprusside (SNP, NO donor), forskolin (FSK, adenylyl cyclase stimulant) and nifedipine, a Ca2+-antagonist (selective L-type calcium antagonist). The vasodilator activity of these compounds was quantified by their vasodilator potency value (pD2) and efficacy (Emax) obtained from their concentration-response curves. PhE (0.1, 0.3, 3 microM) caused isometric responses of 4.8 +/- 0.3, 6.5 +/- 0.3 and 7.8 +/- 0.5 mN, respectively. An increase of the PhE concentration from 0.1 to 3 microM did not influence the response to FSK while it reduced the pD2 of SNP (8.6 +/- 0.1 to 7.35 +/- 0.1). Under these conditions, only the Emax of MCh was reduced (96.3 +/- 4.3% to 43.3 +/- 6.9%). U46 (0.18, 0.3, 1 microM) increased the contractile force by 7.4 +/- 0.4, 8.8 +/- 0.3 and 10.4 +/- 0.3 mN, respectively. Increasing the concentration of U-46 from 0.18 to 1 microM affected only the efficacy of SNP (84 +/- 4.4% to 17 +/- 8.8%) and MCh (64.5 +/- 12.3% to 0.0 +/- 9.2%) and reduced the potency of FSK (7.91 +/- 0.26 to 7.15 +/- 0.10). The concentration of K+-ions from 25 to 30 and 40 mM increased the contractile force by 4.0 +/- 0.4, 7.0 +/- 0.5 and 10.8 +/- 0.4 mN, respectively. The increase in [K+] caused a potency decrease of FSK (7.1 +/- 0.0 to 5.8 +/- 0.0) whereas both efficacy and potency were reduced for SNP (95.6 +/- 1.8% to 65.8 +/- 1.9% and 8.7 +/- 0.1 to 7.2 +/- 0.1) and MCh (55.4 +/- 3.5% to 24.5 +/- 0.8% and 7.4 +/- 0.3 to 6.1 +/- 0.4). Inhibiting of the endothelial NO production by L-NAME 100 microM resulted after pre-contraction with PhE and potassium in comparable differences in properties for SNP. Pre-contraction with St 587 1, 3, 10 and 30 microM shows comparable results after nifedepine relaxation. The present experiments clearly demonstrate that the characteristics of the applied pre-contraction strongly, but differentially influence both the potency and efficacy of various vasodilator drugs in vitro. Accordingly, in vitro characterization of vasodilator drugs should be performed under a carefully standardized protocol of pre-contraction.

Phosphorylation of kinase-related protein (telokin) in tonic and phasic smooth muscles

KRP (telokin), an independently expressed C-terminal myosin-binding domain of smooth muscle myosin light chain kinase (MLCK), has been reported to have two related functions. First, KRP stabilizes myosin filaments (Shirinsky et al., 1993, J. Biol. Chem. 268, 16578-16583) in the presence of ATP. Secondly, KRP can modulate the level of myosin light chain phosphorylation. In this latter role, multiple mechanisms have been suggested. One hypothesis is that light chain phosphorylation is diminished by the direct competition of KRP and MLCK for myosin, resulting in a loss of contraction. Alternatively, KRP, through an unidentified mechanism, accelerates myosin light chain dephosphorylation in a manner possibly enhanced by KRP phosphorylation. Here, we demonstrate that KRP is a major phosphoprotein in smooth muscle, and use a comparative approach to investigate how its phosphorylation correlates with sustained contraction and forskolin-induced relaxation. Forskolin relaxation of precontracted artery strips caused little increase in KRP phosphorylation, while treatment with phorbol ester increased the level of KRP phosphorylation without a subsequent change in contractility. Although phorbol ester does not induce contraction of phasic tissues, the level of KRP phosphorylation is increased. Phosphopeptide maps of KRP from both tissues revealed multiple sites of phosphorylation within the N-terminal region of KRP. Phosphopeptide maps of KRP from gizzard were more complex than those for KRP from artery consistent with heterogeneity at the amino terminus and/or additional sites. We discovered through analysis of KRP phosphorylation in vitro that Ser12, Ser15 and Ser15 are phosphorylated by cAMP-dependent protein kinase, mitogen-activated protein (MAP) kinase and glycogen synthase kinase 3 (GSK3), respectively. Phosphorylation by GSK3 was dependent upon prephosphorylation by MAP kinase. This appears to be the first report of conditional or hierarchical phosphorylation of KRP. Peptides consistent with such multiple phosphorylations were found on the in vivo phosphopeptide maps of avian KRP. Collectively, the available data indicate that there is a complex relationship between the in vivo phosphorylation states of KRP and its effects on relaxation in smooth muscle.

Effect of 5-aminoimidazole-4-carboxamide riboside (AICA-r) on isolated thoracic aorta responses in streptozotocin-diabetic rats

Diabetes mellitus alters the vascular responsiveness to several vasoconstrictors and vasodilators. 5-amino-4-imidazole-carboxamide riboside (AICA-r), a nucleoside corresponding to AICA-ribotide and an intermediate of the de novo pathway of purine biosynthesis, was recently proposed as a new insulinotropic tool in non-insulin-dependent diabetes mellitus. The aim of the present study was to define whether AICA-r affects altered vascular responsiveness to vasoconstrictors and vasodilators in the thoracic aorta of neonatal streptozotocin (STZ)-diabetic rats. The results of this study indicate that a 1-month treatment with AICA-r significantly increases the body weight in diabetic rats; significantly decreases the blood glucose level of diabetic rats (from 302+/-47 to 135+/-11 mg/dL, p<0.001); does not significantly affect the fast, slow, and total components of responses to noradrenaline in all the experimental groups; reverses the increased Emax values of noradrenaline in diabetic rats to near-control values; reverses the completely abolished responses of acetylcholine (pD2 and percent relaxation) in diabetic rats to control values; and reverses the decreased pD2 values of sodium nitroprussiate in diabetic rats to control values. In conclusion, AICA-r treatment in neonatal STZ-diabetic rats improved increased blood glucose levels, accelerated weight gain, reversed endothelial dysfunction, and normalized vascular responses.

Cyclic nucleotide phosphodiesterase 1C promotes human arterial smooth muscle cell proliferation

Proliferation of arterial smooth muscle cells (SMCs) is a key event in the formation of advanced atherosclerotic lesions and restenosis after angioplasty. Cyclic nucleotides (cAMP and cGMP) inhibit arterial SMC proliferation, and elevation of cyclic nucleotides reduces neointimal formation after angioplasty in animal models. Degradation of cAMP and cGMP is catalyzed by cyclic nucleotide phosphodiesterases (PDEs). One of these, PDE1C, hydrolyzes cAMP and cGMP and is expressed in proliferating human SMCs but is absent in quiescent human aorta. Thus, PDE1C expression is low in cultured human SMCs made quiescent by attaching to fibrillar collagen type I. After release from the fibrillar collagen, PDE1C expression is induced and associated with traverse through S-phase of the cell cycle. Further, PDE1C is expressed in vivo in human fetal aorta containing proliferating SMCs, but not in newborn aorta in which SMC proliferation has ceased. Inhibition of PDE1C in SMCs isolated from normal aorta or from lesions of atherosclerosis using antisense oligonucleotides or a PDE1 inhibitor results in suppression of SMC proliferation. In conclusion, PDE1C expression is a marker of human SMC proliferation ex vivo and in vivo. Inhibition of PDE1C leads to inhibition of human SMC proliferation. Because PDE1C is absent in quiescent SMCs, PDE1C inhibitors may target proliferating SMCs in lesions of atherosclerosis or restenosis.

Role of PI3-kinase in isoproterenol and IGF-1 induced ecNOS activity

Phosphatidylinositol 3-kinase (PI3-K) has been shown to mediate insulin and insulin-like growth factor-1 (IGF-1)-induced nitric oxide (NO) generation and, thus, vascular tone. A role for PI3-K in G-protein-coupled receptor signal transduction has been reported. As beta (beta2)-adrenergic vascular actions are partly dependent on NO, we have investigated the role of PI3-K in isoproterenol (Iso) and IGF-1 induced endothelial NO synthase (ecNOS) activity in rat aortic endothelial cells (RAEC). Cell lysates of RAEC, exposed to Iso (10 micromol/L) for 5 min and 6 h, and to IGF-1 (100 nM) for 10 min and 6 h, or pretreated with PI3-K inhibitor Wortmannin (WT), were used for measuring PI3-K activity, p85kDa regulatory protein, and citrulline production. Results show that Iso and IGF-1 increased a p85 subunit and citrulline production, and also enhanced 32P incorporation into PIP3. Pretreatment with WT inhibited Iso-stimulated ecNOS, as well as, PI3-K activity. Iso enhanced association of ecNOS with the triton X-100-insoluble fraction of RAEC. These data indicate that the endothelial cell PI3-K pathway mediates, in part, the release of NO and subsequent vasorelaxation in response to this beta-agonist, as well as, IGF-1.

Phosphorylation and regulation of G-protein-activated phospholipase C-beta 3 by cGMP-dependent protein kinases

Among the drugs that are known to relax the vascular smooth muscle and regulate other cellular functions, beta-adrenergic agonists and nitric oxide-containing compounds are some of the most effective ones. The mechanisms of these drugs are thought to lower agonist-induced intracellular [Ca(2+)] by increasing intracellular cAMP and cGMP, activating their respective protein kinases. However, the physiological targets of cyclic nucleotide-dependent protein kinases are not clear. The molecular basis for the regulation of intracellular Ca(2+) by signaling pathways coupled to cyclic nucleotides is not well defined. G-protein-activated phospholipase C (PLC-beta) catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphates to generate diacylglycerol and inositol 1,4,5-triphosphate, leading to the activation of protein kinase C and the mobilization of intracellular Ca(2+). In this study, we shown that G-protein-activated PLC enzymes are the potential targets of cGMP-dependent protein kinases (PKG). PKG can directly phosphorylate PLC-beta2 and PLC-beta3 in vitro with purified proteins and in vivo with metabolic labeling. Phosphorylation of PLC-beta leads to the inhibition of G-protein-activated PLC-beta3 activity by 50-70% in COS-7 cell transfection assays. By using phosphopeptide mapping and site-directed mutagenesis, we further identified two key phosphorylation sites for the regulation of PLC-beta3 by PKG (Ser(26) and Ser(1105)). Mutation at these two sites (S26A and S1105A) of PLC-beta3 completely blocked the phosphorylation of PLC-beta3 protein catalyzed by PKG. Furthermore, mutation of these serine residues removed the inhibitory effect of PKG on the activation of the mutant PLC-beta3 proteins by G-protein subunits. Our results suggest a molecular mechanism for the regulation of G-protein-mediated intracellular [Ca(2+)] by the NO-cGMP-dependent signaling pathway.

Regulation of glucose transport in aortic smooth muscle cells by cAMP and cGMP

We have studied the ability of cGMP and cAMP to modulate platelet-derived growth factor (PDGF)-stimulated 2-deoxy-D-glucose (deGlc) transport in primary cultures of vascular smooth muscle cells (VMSC) from rat aorta. PDGF stimulated deGlc transport in a time- and concentration-dependent manner. 8-Bromo-cGMP and atrial natriuretic peptide(1-28) [ANP(1-28)] were found to reduce PDGF-stimulated deGlc transport without affecting basal (unstimulated) transport activity. In contrast, 8-bromo-cAMP and dibutyryl-cAMP stimulated basal deGlc transport 2-fold and were without effect on PDGF-stimulated deGlc transport. 8-Bromo-cGMP also inhibited 8-bromo-cAMP-stimulated deGlc transport. The stimulation of deGlc transport by PDGF was sensitive to the mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) kinase (MEK) inhibitor PD98059, and we show that ERK1/2 was activated by PDGF. Neither 8-bromo-cGMP nor ANP(1-28) inhibited PDGF-stimulated ERK activation, suggesting that the effects of cGMP and ANP(1-28) were not mediated by inhibition of this kinase. Our data also argue against a role for cGMP-dependent protein kinase in mediating the effects of cGMP or ANP(1-28). Collectively, our data suggest that in VSMC: (i) cGMP and cAMP have opposing effects on deGlc transport; (ii) PDGF and cAMP have common elements in the pathways by which they activate deGlc transport; and (iii) a common element may be the target of the cGMP-mediated inhibition of deGlc transport.