Regulation of Ca2+ channel and phosphatase activities by polyamines in intestinal and vascular smooth muscle--implications for cellular growth and contractility

Analysis of interaction between intracellular spermine and transient receptor potential canonical 4 channel: multiple candidate sites of negatively charged amino acids for the inward rectification of transient receptor potential canonical 4

Transient receptor potential canonical 4 (TRPC4) channel is a nonselective calcium-permeable cation channels. In intestinal smooth muscle cells, TRPC4 currents contribute more than 80% to muscarinic cationic current (mIcat). With its inward-rectifying current-voltage relationship and high calcium permeability, TRPC4 channels permit calcium influx once the channel is opened by muscarinic receptor stimulation. Polyamines are known to inhibit nonselective cation channels that mediate the generation of mIcat. Moreover, it is reported that TRPC4 channels are blocked by the intracellular spermine through electrostatic interaction with glutamate residues (E728, E729). Here, we investigated the correlation between the magnitude of channel inactivation by spermine and the magnitude of channel conductance. We also found additional spermine binding sites in TRPC4. We evaluated channel activity with electrophysiological recordings and revalidated structural significance based on Cryo-EM structure, which was resolved recently. We found that there is no correlation between magnitude of inhibitory action of spermine and magnitude of maximum current of the channel. In intracellular region, TRPC4 attracts spermine at channel periphery by reducing access resistance, and acidic residues contribute to blocking action of intracellular spermine; channel periphery, E649; cytosolic space, D629, D649, and E687.

Modulatory effect of intestinal polyamines and trace amines on the spontaneous phasic contractions of the isolated ileum and colon rings of mice

Background: Gastrointestinal motility modulatory factors include substances of the intestinal content, such as polyamines and trace amines (TAs), the focus of this study.

Methods: The amines of food, intestinal content and from faecal bacteria of Swiss mice were determined by HPLC and functionally characterised in isolated distal ileum and medial colon rings.

Results: Mouse food and intestinal content contain polyamines (spermidine>putrescine>spermine) and TAs (isoamylamine>cadaverine). Intestinal bacteria mainly produce putrescine and cadaverine. The amines inhibited the spontaneous motility of the ileum (0.1-3 mM) and colon rings (0.01-3 mM, with lower IC₅₀), with: spermine~isoamylamine~spermidine. Spermine inhibition was tetrodotoxin (TTX)-insensitive, while isoamylamine was TTX-sensitive, suggesting neural control. Mainly in the ileum, isoamylamine (3 mM) elicited acute effects modified by TTX, atropine and propranolol, and suppressed by spermine (3 mM), not being localized at the smooth muscle level. The amines assayed (3 mM), except putrescine and cadaverine in the ileum and isoamylamine in the colon, antagonised acetylcholine (ACh, 0.1 mM)-elicited phasic contractions. Isoamylamine and spermine in colon relaxed KCl (100 mM)-elicited tonic contractions, suggesting an effect on smooth muscle, but did not justify the suppression of motility caused by spermine and isoamylamine.

Conclusions: Polyamines and TAs of the intestinal content might act on chemosensors and modulate intestinal peristalsis.

Metabolic Signature of Remote Ischemic Preconditioning Involving a Cocktail of Amino Acids and Biogenic Amines

BACKGROUND

Remote ischemic preconditioning (RIPC) is an attractive therapeutic procedure for protecting the heart against ischemia/reperfusion injury. Despite evidence of humoral mediators transported through the circulation playing a critical role, their actual identities so far remain unknown. We sought to identify plasmatic RIPC-induced metabolites that may play a role.

METHODS AND RESULTS

Rat plasma samples from RIPC and control groups were analyzed using a targeted metabolomic approach aimed at measuring 188 metabolites. Principal component analysis and orthogonal partial least-squares discriminant analysis were used to identify the metabolites that discriminated between groups. Plasma samples from 50 patients subjected to RIPC were secondarily explored to confirm the results obtained in rats. Finally, a combination of the metabolites that were significantly increased in both rat and human plasma was injected prior to myocardial ischemia/reperfusion in rats. In the rat samples, 124 molecules were accurately quantified. Six metabolites (ornithine, glycine, kynurenine, spermine, carnosine, and serotonin) were the most significant variables for marked differentiation between the RIPC and control groups. In human plasma, analysis confirmed ornithine decrease and kynurenine and glycine increase following RIPC. Injection of the glycine and kynurenine alone or in combination replicated the protective effects of RIPC seen in rats.

CONCLUSIONS

We have hereby reported significant variations in a cocktail of amino acids and biogenic amines after remote ischemic preconditioning in both rat and human plasma.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01390129.

Effects of Polyamines on Human Umbilical Artery Tone In Vitro

OBJECTIVE

Polyamines act as endogenous modulators of cell function and excitability. There are no data in relation to their effects on the human fetoplacental circulation. The aim of this study was to investigate the effects of the polyamines, spermine, and spermidine on human umbilical artery resistance in vitro.

METHODS

Isometric tension recordings were performed under physiologic conditions on human umbilical arterial rings (n = 12). The in vitro effects of spermine and spermidine (at concentrations ranging between 10(-9) M to 10(-3) M) were measured, and compared with those measured in vehicle control experiments. The maximal inhibition (MMI) at the highest concentration and the pD2 (-log EC50) values for each compound were calculated and compared.

RESULTS

Spermine and spermidine exerted a potent relaxant effect on human umbilical arterial tone in comparison to vehicle control experiments. The MMI +/- SEM for spermine was 18.41 +/- 1.437% (n = 6; P <.001) and for spermidine was 38.31 +/- 3.572% (n = 6; P <.001). There was no difference observed between the pD2 +/- SEM values for spermine (5.78 +/- 1.54; n = 6) and spermidine (6.27 +/-0.85; n = 6) (P = .517).

CONCLUSION

The polyamines spermine and spermidine exert a potent relaxant effect on human umbilical artery tone suggestive of an endogenous role for these compounds in vasomotor regulation of the fetoplacental circulation.

Inhibition of polyamine formation antagonizes vascular smooth muscle cell proliferation and preserves the contractile phenotype

The polyamines putrescine, spermidine and spermine play essential roles in cell proliferation and migration, two processes involved in the development of vascular disease. Thus, intervention with polyamine formation may represent a way to inhibit unwanted vascular smooth muscle cell (VSMC) proliferation. The aim of the present study was to assess the importance of polyamines for VSMC proliferation and vascular contractility. The rate-limiting step in polyamine biosynthesis is catalysed by ornithine decarboxylase (ODC). Treatment with α-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, reduced DNA synthesis in primary rat VSMCs in a concentration-dependent manner with an IC50 value of 100 μM. Moreover, DFMO reduced VSMC migration assessed in a scratch assay. The DFMO-induced attenuation of VSMC proliferation was associated with lowered cellular amount of polyamines. The antiproliferative effect of DFMO was specific because supplementation with polyamines reversed the effect of DFMO on proliferation and normalized cellular polyamine levels. Isometric force recordings in cultured rat tail artery rings showed that DFMO counteracts the decrease in contractility caused by culture with foetal bovine serum as growth stimulant. We conclude that inhibition of polyamine synthesis by DFMO may limit the first wave of cell proliferation and migration, which occurs in the acute phase after vascular injury. Besides its antiproliferative effect, DFMO may prevent loss of the smooth muscle contractile phenotype in vascular injury.

Curcumin prevents leptin raising glucose levels in hepatic stellate cells by blocking translocation of glucose transporter-4 and increasing glucokinase

BACKGROUND AND PURPOSE

Hyperleptinemia is commonly found in obese patients, associated with non-alcoholic steatohepatitis and hepatic fibrosis. Hepatic stellate cells (HSCs) are the most relevant effectors during hepatic fibrogenesis. We recently reported that leptin stimulated HSC activation, which was eliminated by curcumin, a phytochemical from turmeric. This study was designed to explore the underlying mechanisms, focusing on their effects on intracellular glucose in HSCs. We hypothesized that leptin stimulated HSC activation by elevating the level of intracellular glucose, which was eliminated by curcumin by inhibiting the membrane translocation of glucose transporter-4 (GLUT4) and inducing the conversion of glucose to glucose-6-phosphate (G-6-P).

EXPERIMENTAL APPROACH

Levels of intracellular glucose were measured in rat HSCs and immortalized human hepatocytes. Contents of GLUT4 in cell fractions were analysed by Western blotting analyses. Activation of signalling pathways was assessed by comparing phosphorylation levels of protein kinases.

KEY RESULTS

Leptin elevated the level of intracellular glucose in cultured HSCs, which was diminished by curcumin. Curcumin suppressed the leptin-induced membrane translocation of GLUT4 by interrupting the insulin receptor substrates/phosphatidyl inositol 3-kinase/AKT signalling pathway. Furthermore, curcumin stimulated glucokinase activity, increasing conversion of glucose to G-6-P.

CONCLUSIONS AND IMPLICATIONS

Curcumin prevented leptin from elevating levels of intracellular glucose in activated HSCs in vitro by inhibiting the membrane translocation of GLUT4 and stimulating glucose conversion, leading to the inhibition of HSC activation. Our results provide novel insights into mechanisms of curcumin in inhibiting leptin-induced HSC activation.

Curcumin attenuates the effects of insulin on stimulating hepatic stellate cell activation by interrupting insulin signaling and attenuating oxidative stress

Hyperinsulinemia associated with type II diabetes mellitus (T2DM) is a risk factor for non-alcoholic steatohepatitis (NASH) and hepatic fibrosis. Hepatic stellate cells (HSCs) are the major effectors in collagen production during hepatic fibrogenesis. Elevated levels of insulin stimulate HSC activation. In addition to its anti-diabetic effects, the antioxidant curcumin, the yellow pigment in curry from turmeric, suppresses HSC activation and protects the liver from fibrogenesis in vitro and in vivo. This study aims at evaluating the effect of curcumin on insulin-induced HSC activation and further elucidating the underlying mechanisms. We report that curcumin dose-dependently eliminates insulin-induced HSC activation by suppressing expression of type I collagen gene and other key genes relevant to HSC activation. Additional experiments indicate that curcumin interrupts insulin signaling in HSCs by reducing the phosphorylation level of insulin receptor (InsR) and suppressing gene expression of InsR. Furthermore, curcumin attenuates insulin-induced oxidative stress in HSCs by inducing gene expression of glutamate-cysteine ligase (GCL), leading to de novo synthesis of glutathione and the suppression of gene expression of InsR. These results support our initial hypothesis that curcumin inhibits the effects of insulin on stimulating HSC activation by interrupting insulin signaling and attenuating oxidative stress. Our results provide novel insights into the mechanisms by which curcumin inhibits the insulin-induced HSC activation.

Curcumin eliminates leptin's effects on hepatic stellate cell activation via interrupting leptin signaling

Nonalcoholic steatohepatitis (NASH) is commonly found in patients with obesity and is often accompanied with abnormally elevated levels of plasma leptin, i.e. hyperleptinemia. A relatively high population of NASH patients develops hepatic fibrosis, even cirrhosis. Hepatic stellate cells (HSCs) are the major effector cells during liver fibrogenesis and could be activated by leptin. The antioxidant curcumin, a phytochemical from turmeric, has been shown to suppress HSC activation in vitro and in vivo. This project is to evaluate the effect of curcumin on leptin-induced HSC activation and to elucidate the underlying mechanisms. We hypothesize that curcumin abrogates the stimulatory effect of leptin on HSC activation by interrupting leptin signaling and attenuating leptin-induced oxidative stress. Curcumin eliminates the stimulatory effects of leptin on regulating expression of genes closely relevant to HSC activation. Curcumin interrupts leptin signaling by reducing phosphorylation levels of leptin receptor (Ob-R) and its downstream intermediators. In addition, curcumin suppresses gene expression of Ob-R in HSCs, which requires the activation of endogenous peroxisome proliferator-activated receptor-gamma and de novo synthesis of glutathione. In conclusion, our results demonstrate that curcumin abrogates the stimulatory effect of leptin on HSC activation in vitro by reducing the phosphorylation level of Ob-R, stimulating peroxisome proliferator-activated receptor-gamma activity, and attenuating oxidative stress, leading to the suppression of Ob-R gene expression and interruption of leptin signaling. These results provide novel insights into therapeutic mechanisms of curcumin in inhibiting HSC activation and intervening liver fibrogenesis associated with hyperleptinemia in NASH patients.

Functional K(ATP) channels in the rat retinal microvasculature: topographical distribution, redox regulation, spermine modulation and diabetic alteration

The essential task of the circulatory system is to match blood flow to local metabolic demand. However, much remains to be learned about this process. To better understand how local perfusion is regulated, we focused on the functional organization of the retinal microvasculature, which is particularly well adapted for the local control of perfusion. Here, we assessed the distribution and regulation of functional K(ATP) channels whose activation mediates the hyperpolarization induced by adenosine. Using microvascular complexes freshly isolated from the rat retina, we found a topographical heterogeneity in the distribution of functional K(ATP) channels; capillaries generate most of the K(ATP) current. The initiation of K(ATP)-induced responses in the capillaries supports the concept that the regulation of retinal perfusion is highly decentralized. Additional study revealed that microvascular K(ATP) channels are redox sensitive, with oxidants increasing their activity. Furthermore, the oxidant-mediated activation of these channels is driven by the polyamine spermine, whose catabolism produces oxidants. In addition, our observation that spermine-dependent oxidation occurs predominately in the capillaries accounts for why they generate most of the K(ATP) current detected in retinal microvascular complexes. Here, we also analysed retinal microvessels of streptozotocin-injected rats. We found that soon after the onset of diabetes, an increase in spermine-dependent oxidation at proximal microvascular sites boosts their K(ATP) current and thereby virtually eliminates the topographical heterogeneity of functional K(ATP) channels. We conclude that spermine-dependent oxidation is a previously unrecognized mechanism by which this polyamine modulates ion channels; in addition to a physiological role, spermine-dependent oxidation may also contribute to microvascular dysfunction in the diabetic retina.

Polyamine synthesis inhibition induces S phase cell cycle arrest in vascular smooth muscle cells

Polyamines are important for cell growth and proliferation and they are formed from arginine and ornithine via arginase and ornithine decarboxylase (ODC). Arginine may alternatively be metabolised to NO via NO synthase. Here we study if vascular smooth muscle cell proliferation can be reversed by polyamine synthesis inhibitors and investigate their mechanism of action. Cell proliferation was assessed in cultured vascular smooth muscle A7r5 cells and in endothelium-denuded rat arterial rings by measuring [3H]-thymidine incorporation and by cell counting. Cell cycle phase distribution was determined by flow cytometry and polyamines by HPLC. Protein expression was determined by Western blotting. The ODC inhibitor DFMO (1-10 mM) reduced polyamine concentration and attenuated proliferation in A7r5 cells and rat tail artery. DFMO accumulated cells in S phase of the cell cycle and reduced cyclin A expression. DFMO had no effect on cell viability and apoptosis as assessed by fluorescence microscopy. Polyamine concentration and cellular proliferation were not affected by the arginase inhibitor NOHA (100-200 microM) and the NO synthase inhibitor L-NAME (100 microM). Lack of effect of NOHA was reflected by absence of arginase expression. Polyamine synthesis inhibition attenuates vascular smooth muscle cell proliferation by reducing DNA synthesis and accumulation of cells in S phase, and may be a useful approach to prevent vascular smooth muscle cell proliferation in cardiovascular diseases.

Antioxidative properties of human milk and spermine are not related to expression of Hsp 70

AIM

Heat shock proteins (Hsps) have been detected in various tissues, including those in the intestines, and play a role in cellular protection. Polyamines, such as spermine (SPM), are found in human milk (HM) and act as antioxidants. We hypothesized that the antioxidative property of SPM is related to the expression of Hsp and examined this relationship in an intestinal epithelial cell (IEC) line.

METHOD

(i) Confluent IEC-6 cells were exposed to mild heat shock (43 degrees C, 1 h) and then allowed to recover at 37 degrees C for 24 h. Hydrogen peroxide (H(2)O(2)) was applied to induce oxidative stress and cell viability was evaluated. (ii) Cells were exposed to mild heat shock or pre-incubated with HM or pre-incubated with 5 microM SPM for 24 h. Hsp70 expression in IEC-6 cells was analysed by Western blot.

RESULTS

The survival rate of cells treated with mild heat shock after H(2)O(2) challenge was significantly higher than that of non-pretreated cells. Western blot analysis demonstrated that Hsp70 was expressed in IEC-6 cells treated with mild heat shock but not in IEC-6 cells pre-incubated with HM or 5 microM SPM.

CONCLUSION

Mild heat shock treatment induces Hsp70, which acts as an antioxidant in IEC-6 cells, but HM or SPM does not induce Hsp70 in this system.

Effects of spermine on the relaxation response of rat detrusor smooth muscles

Endogenous polyamines are known to influence excitation-contraction coupling in smooth muscle. This study was designed to determine the effects of the polyamines spermine, spermidine, and putrescine on the contractile responses of rat detrusor smooth muscles. Under physiological conditions, isometric tension recordings were made of isolated bladder strips from excised rat bladder. The effects of spermine, spermidine, and putrescine (1 mM each) on the bladder contractions induced by various agents, i.e., acetylcholine, bethanechol, high-K, and tetraethylammonium (TEA) were measured. A conventional patch clamp technique was used in whole cell mode with single smooth muscle cells of rat bladder. Calcium channel currents were recorded to determine the effects of spermine on channel activities. Polyamines elicited a concentration-dependent relaxations on the contractile agents induced contractures. Spermine showed the most potent relaxation effect of the polyamines examined, and relaxed the contractions induced by the agents. Calcium channel activities were significantly reduced by adding 1 mM spermine to the bath. We concluded that spermine exerts a potent relaxant effect on rat bladder smooth muscle, and this effect appears to be mediated by calcium channel antagonism.

Role of polyamines in myocardial ischemia/reperfusion injury and their interactions with nitric oxide

Polyamines (putrescine, spermidine, and spermine) are present in all higher eukaryotic cells and are essential for cell growth, differentiation and apoptosis. Sharing common precursor with polyamines, nitric oxide (NO) is associated with myocardial ischemia/reperfusion injury by the generation of peroxynitrite. Although polyamines have been implicated in tissue ischemia injury, their metabolism and interactions with NO in myocardial ischemia/reperfusion injury have not been fully understood. In our experiment, when Langendorff perfused rat hearts were subjected to 40 min ischemia without reperfusion, both ornithine decarboxylase (ODC) and Spermidine/spermine N(1)-acetyltransferase (SSAT) activities were up-regulated and putrescine accumulated. While after reperfusion, ODC activity decreased and SSAT activity increased, resulting in putrescine accumulation and decreased spermidine and spermine. Meanwhile NO content was increased. In addition, sodium nitroprusside (SNP, a NO donor) decreased ODC activity in cardiac tissue homogenate but increased SSAT activity in a dose-dependent manner. Pre-treatment of isolated heart with N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, an inhibitor of NO synthase) increased ODC activity. Exogenous spermine (1 mM) administration prior to ischemia prevented spermine decrease, reduced cardiac myocyte necrosis and apoptosis, and promoted the recovery of cardiac function after ischemia/reperfusion. These results suggest that acute heart ischemia activates myocardial polyamine stress response characterized by increased ODC and SSAT activities and accumulation of putrescine. Ischemia/reperfusion disturbs polyamine metabolism, and the loss of spermine might be associated with NO increase and thereby influences myocardial cell viability. Exogenous spermine may protect the hearts from myocardial ischemia/reperfusion injury.

Effects of polyamines on contractility of guinea-pig gastric smooth muscle

This study was designed to investigate the effects of polyamines on mechanical contraction and voltage-dependent calcium current (VDCC) of guinea-pig gastric smooth muscle. Mechanical contraction and calcium channel current I(Ba) were recorded by isometric tension recording and whole-cell patch clamp technique. Spermine, spermidine and putrescine inhibited spontaneous contraction of the gastric smooth muscle in a concentration-dependent manner. Spermine (2 mM) reduced high K+ (50 mM)-induced contraction to 16+/-6.4% of the control (n=9), and significantly inhibited I(Ba) in a reversible manner (p<0.05; IC50=0.8 mM). Pre- and post-treatment of tissue with spermine (2-5 mM, n=10) also inhibited acetylcholine (10 microM)-induced phasic contraction to 5+/-6.4% of the control. Inhibitory effect of spermine on I(Ba) was observed at a wide range of test potentials of current/voltage (I/V) relationship (p<0.05), and steady-state activation of I(Ba) was shifted to the right by spermine (p<0.05). Spermidine and putrescine (1 mM each) also inhibited I(Ba) to 51+/-5.7% and 81+/-5.3% of the control, respectively. And putrescine (1 mM) inhibited I(Ba) at whole tested potentials (p<0.05) without significant change of kinetics (p<0.05). Finally, 5 mM putrescine also inhibited high K+-induced contraction to 53+/-7.1% of the control (n=4). These findings suggest that polyamines inhibit contractions of guinea-pig gastric smooth muscle via inhibition of VDCC.

Androgens differentially potentiate mouse intestinal smooth muscle by nongenomic activation of polyamine synthesis and Rho kinase activation

We demonstrate that testosterone and its active metabolite 5alpha-dihydrotestosterone acutely (approximately 30 min) potentiate mouse ileal, but not duodenal, muscle activity. Androgens augment the amplitude of spontaneous peak-to-peak oscillations, alter the spontaneous activity frequency spectrum, and increase the amplitude of calcium-induced and carbachol-induced contractions. Concentration-dependence analyses revealed that maximal potentiation (449-910%) occurred at physiological concentrations of androgens (100 pM to 10 nM) with EC50 values in the picomolar range (8-20 pM). Western blot analyses using an antiandrogen receptor (anti-AR) antibody revealed the presence of two different AR proteins migrating at 87 and 110 kDa in ileal, but not duodenal, extracts. Androgen-induced potentiation was prevented by preincubation with AR antagonists flutamide or cyproterone acetate but was unaffected by pretreatment with cycloheximide plus actinomycin D, indicating that potentiation was mediated by ARs via a novel nongenomic mechanism. Androgen effects were mimicked by polyamines putrescine and spermine and were blocked by the ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase inhibitors alpha-difluoromethylornithine and berenil, respectively. Accordingly, androgens increase alpha-difluoromethylornithine-sensitive ornithine-decarboxylase- mediated L-ornithine decarboxylation in ileal tissues within the same time course as isometric potentiation. Both putrescine and dihydrotestosterone induced Ca2+ sensitization of ionomycin-permeabilized ileal smooth muscle. Finally, inhibition of the Rho kinase (ROK) pathway with the specific inhibitor Y27632 completely prevented androgen-induced potentiation. In agreement, androgens elicited ROK-induced Ser19 phosphorylation of myosin light chain 2 in ileal muscle. These data indicate that androgens potentiate ileal contractile activity by an AR-dependent nongenomic mechanism involving intracellular polyamine signaling and Ca2+ sensitization via ROK activation.

Regulation of apoptosis signal-regulating kinase 1 (ASK1) by polyamine levels via protein phosphatase 5

Recent evidence has implicated the protein phosphatase PP5 in a variety of signaling pathways. Whereas several proteins have been identified that interact with PP5 and regulate its activity, a possibility of its regulation by second messengers remains speculative. Activation of PP5 in vitro by polyunsaturated fatty acids (e.g. arachidonic acid) and fatty acyl-CoA esters (e.g. arachidonoyl-CoA) has been reported. We report here that PP5 is strongly inhibited by micromolar concentrations of a natural polyamine spermine. This inhibition was observed both in assays with a low molecular weight substrate p-nitrophenyl phosphate as well as phosphocasein and apoptosis signal-regulating kinase 1 (ASK1), thought to be a physiological substrate of PP5. Furthermore, a decrease in polyamine levels in COS-7 cells induced by alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, led to accelerated dephosphorylation of oxidative stress-activated ASK1. This effect was suppressed by okadaic acid and by siRNA-mediated PP5 depletion, indicating that the effect of polyamine levels on ASK1 dephosphorylation was mediated by PP5. In line with the decreased ASK1 activation, polyamine depletion in COS-7 cells abrogated oxidative stress-induced activation of caspase-3, which executes ASK1-induced apoptosis, as well as caspase-3 activation induced by ASK1 overexpression, but had no effect on basal caspase-3 activity. These results implicate polyamines, emerging intracellular signaling molecules, as potential physiological regulators of PP5. Our findings also suggest a novel mechanism of the anti-apoptotic action of a decrease in polyamine levels via de-inhibition of PP5 and accelerated dephosphorylation and deactivation of ASK1.

Effects of polyamines on the muscarinic receptor-operated cation current in guinea-pig ileal smooth muscle myocytes

The effects of extracellular and intracellular polyamines (PAs), spermine and putrescine, on the cation current (mI(CAT)) evoked either by activating muscarinic receptors with carbachol or by intracellularly applied GTPgammaS (in the absence of carbachol) were studied using patch-clamp recording techniques in single guinea-pig ileal myocytes. Extracellular spermine and putrescine rapidly and reversibly inhibited mI(CAT) in a concentration- and voltage-dependent manner with the IC(50) values at -40 mV of about 1 and 5 mM, respectively. Membrane depolarization relieved the blocking action of PAs although cation conductance activation curve remained N-shaped. The inhibition was similar for both carbachol- and GTPgammaS-evoked currents, suggesting that the cation channel rather than the muscarinic receptor was the primary site of the PA action. In outside-out membrane patches, both cation channel unitary conductance and open probability were reduced. In perforated-patch experiments used to retain cytoplasmic PAs sustained 100 microM carbachol-induced mI(CAT) was significantly smaller (478 +/- 76 pA, n = 7) compared to that recorded using conventional whole-cell configuration with nominally PA-free pipette solution (1314 +/- 76 pA, n = 12), but comparable in size to mI(CAT) with 0.3 mM spermine in the pipette solution (509 +/- 41 pA, n = 19). Intracellular putrescine inhibited mI(CAT) less potently compared to spermine. In conclusion, these results show a novel role of intestinal PAs in mI(CAT) inhibition, which can contribute to their well-known suppressing effect on the gastrointestinal smooth muscle excitability and contractility.

Polyamine Synthesis Inhibition Attenuates Vascular Smooth Muscle Cell Migration

Vascular smooth muscle cell migration, occurring after intimal injury, is a substantial clinical problem in atherosclerosis and restenosis after stenting. Here we investigate the effects of polyamine synthesis inhibition on vascular smooth muscle cell migration after maximal and submaximal growth stimulation with PDGF-AB or FCS. Vascular smooth muscle cells were obtained from mouse aorta explants. These cells coexpressed smooth muscle alpha-actin, PDGFRalpha and PDGFRbeta as demonstrated by immunocytochemistry. Treatment with a high (100 ng/ml) concentration of PDGF-AB stimulated DNA synthesis 6-fold and markedly elevated cell migration. PDGF-AB (100 ng/ml) increased cellular spermidine concentration 2-fold, but had no effect on spermine or putrescine levels. Treatment with the polyamine synthesis inhibitors CGP48664 (1 microM) and DFMO (5 mM) prevented the PDGF-AB-induced increase in spermidine and reduced spermine concentrations, but had no effect on PDGF-AB-stimulated DNA synthesis or cell migration. Cell migration after submaximal stimulation with either PDGF-AB (8 ng/ml) or FCS (8%) was, however, inhibited by the polyamine synthesis blockers. In summary, these data show that polyamine synthesis inhibition attenuates vascular smooth muscle cell migration under submaximal growth-stimulating conditions, suggesting that polyamines participate in regulation of cell migration and that treatment with polyamine synthesis inhibitors might reduce vascular smooth muscle cell migration after intimal injury.

Incorporation of alkaline phosphatase into layer-by-layer polyelectrolyte films on the surface of affi-gel heparin beads: physicochemical characterization and evaluation of the enzyme stability

The preparation of functionalized beads in the micrometer size range that can be used to probe the action of immobilized biomolecules on cell cultures during controlled periods of time is of fundamental importance in cell biology. However, the preparation and characterization of such particles is tedious because of their fast sedimentation. It is hence difficult to prepare such beads in a reproducible manner. This highlights the need to prepare an important batch of functionnalized particles and to store them under conditions where the loss of biological activity is minimized. The aim of this paper was to immobilize alkaline phosphatase (AP) as a model enzyme on the surface of Affi-gel heparin beads functionnalized by means of a layer-by-layer (LBL) film made of poly-l-glutamic (PGA) acid and poly-l-lysine (PLL). The enzyme has been adsorbed either on the top of the LBL film or embedded under five polyelectrolyte layers. When embedded, the enzyme was not released in buffer and retained more than 30% of its initial activity after 3 months of storage at 4 degrees C. However, when the enzyme was adsorbed on top of the LBL film, about 80% of the adsorbed enzyme was released in the buffer after a few days of storage. Longer storage did not lead to any further desorption and the remaining enzyme displayed the same evolution of its activity with time as the embedded enzyme. The time evolution of the enzyme activity on the beads is compared with that in solution alone and in the presence of PGA and PLL separately.