Biomedical subjects

F Martel

Publications and source records attributed to F Martel.

At least 19 recordsLinked to original sources

PubMed2006

Recent advances on the importance of the serotonin transporter SERT in the rat intestine.

Serotonin (5-HT) is present in high concentration in enterochromaffin cells throughout the gastrointestinal tract, where it plays a very important role, being involved, e.g., in peristaltic and secretory reflexes in response to chemical or mechanical stimuli of the gut. Intestinal 5-HT is inactivated by metabolic degradation after cellular uptake mediated by the serotonin transporter SERT. This mini-review summarizes some recent data obtained by our group on the importance, regional distribution and cell membrane localization of SERT in the rat intestine. From our results, we conclude that SERT is located both at the apical and basolateral cell membranes of intestinal epithelial cells in the three intestinal regions studied: jejunum, ileum and colon. Moreover, we also conclude that inhibition of SERT causes an increase in transmural transport of 5-HT in these three intestinal segments, probably because it increases the extracellular concentration of 5-HT. Consequently, SERT inhibition will be able to cause an increase in the physiological responses of the tissue to this amine. The repercussions of this phenomenon are discussed.

Animals↗

PubMed2005

Modulation of MPP+ uptake by tea and some of its components in Caco-2 cells.

The entry of most xeno/endobiotics into the organism is limited by their intestinal absorption. The interference of certain foods with the therapeutic efficacy of drugs or with chemical toxicity is becoming evident and growing attention is being given to these subjects. The aim of this work was to study the effect of green tea (GT) and black tea (BT), as well as some of their components, on the transport of organic cation molecules. For this purpose, 3H-MPP+ (radiolabeled 1-methyl-4-phenylpyridinium) was used as a model organic cation and Caco-2 cells were used as an intestinal epithelial model. Our results showed that both GT and BT significantly increased 3H-MPP+ absorption in these cells. Additionally, we studied the effect of epigallocatechin-3-gallate (EGCG), myricetin, caffeine, and theophylline. Whereas EGCG (2 mM) increased, myricetin (50 microM) and caffeine (1 mM) decreased, and theophylline (1 mM) had no effect on the uptake of 3H-MPP+ into Caco-2 cells. When GT was supplemented with caffeine or theophylline, we observed a partial loss of its effect. When BT was supplemented with EGCG, its ability to increase 3H-MPP+ uptake was much more pronounced than that observed with BT alone. In conclusion, this study showed that GT and BT might interfere with the absorption of the model organic cation MPP+ by the intestinal epithelium. Since important compounds are organic cations, the consequences of this interference may have an impact on human health. Although this constitutes only preliminary work and further studies are needed, tea should be included in the growing list of foodstuffs that have the potential to be involved in food-drug interactions.

1-Methyl-4-phenylpyridinium↗

PubMed2005

Discovery of the short gamma-ray burst GRB 050709.

Gamma-ray bursts (GRBs) fall into two classes: short-hard and long-soft bursts. The latter are now known to have X-ray and optical afterglows, to occur at cosmological distances in star-forming galaxies, and to be associated with the explosion of massive stars. In contrast, the distance scale, the energy scale and the progenitors of the short bursts have remained a mystery. Here we report the discovery of a short-hard burst whose accurate localization has led to follow-up observations that have identified the X-ray afterglow and (for the first time) the optical afterglow of a short-hard burst; this in turn led to the identification of the host galaxy of the burst as a late-type galaxy at z = 0.16 (ref. 10). These results show that at least some short-hard bursts occur at cosmological distances in the outskirts of galaxies, and are likely to be caused by the merging of compact binaries.

Journal Article↗

PubMed2005

Intestinal uptake of MPP+ is differently affected by red and white wine.

It is becoming increasingly evident that ingested products, such as wine, may have profound effects on the therapeutic efficacy of certain drugs. As various xeno- and endobiotics are organic cations, the purpose of our study was to examine the modulation of organic cations intestinal apical uptake by red (RW) and white wine (WW). For this purpose, we used RW, WW, the same alcohol-free wines, phenolic compounds and ethanol. The uptake of the organic cation 1-methyl-4-phenylpyridinium (MPP+) was evaluated in Caco-2 cells, an intestinal epithelial cell model. RW and alcohol-free RW increased 3H-MPP+ apical uptake, although the effect of alcohol-free RW was less pronounced. On the other hand, WW and alcohol-free WW decreased the organic cation uptake but the effect of alcohol-free WW was more pronounced. Our results show that the total content in phenolic compounds was 7 times higher, and the dialysis index was about 4 times higher in RW compared to WW. Ethanol, in the same concentration found in wine, caused a significant decrease in 3H-MPP+ apical uptake. The solution containing high molecular weight compounds from dialyzed RW increased 3H-MPP+ apical uptake. In conclusion, the results suggest that RW may increase and WW may reduce the intestinal absorption of organic cations present in the diet, such as drugs or vitamins (e.g. thiamine and riboflavin). As ethanol alone decreased the uptake of MPP+, and alcohol-free RW and WW had a lower potency than intact wine upon the transport, the presence of ethanol is probably important for the solubilisation/bioavailability of the components endowed with the transport modulating activity.

1-Methyl-4-phenylpyridinium↗

PubMed2004

The effect of a series of organic cations upon the plasmalemmal serotonin transporter, SERT.

The aim of this work was to test the effect of a series of organic cations upon the activity of the plasma membrane serotonin transporter (SERT). The experiments were performed using the JAR cell line that constitutively expresses high levels of SERT, and rat intestine, whose mucosal epithelial cells also express SERT. Initial rates of (3)H-serotonin ((3)H-5HT; 200 nM) uptake were not changed by some of the organic cations tested (guanidine, N-methylnicotinamide, choline, atenolol, caffeine and theophylline), but were slightly (15-30%) inhibited by some other organic cations, at the highest concentrations tested (thiamine (3 mM), cimetidine (1 mM) and tetraethylammonium (3 mM)). On the other hand, some other organic cations reduced, in a concentration-dependent manner, uptake of (3)H-5HT by JAR cells (IC(50)s of 0.3, 1.3, 5.4, 89.3, 460 and 748 microM for quinidine, verapamil, propranolol, amiloride, nicotine and clonidine, respectively). Quinidine, clonidine and amiloride seem to be competitive inhibitors of (3)H-5HT uptake, whereas verapamil, nicotine and propranolol appear to be uncompetitive or non-competitive inhibitors. Moreover, quinidine, verapamil and propranolol trans-inhibited (3)H-5HT uptake, whereas clonidine, nicotine and amiloride were devoid of effect. Finally, these six organic cations were able to significantly increase the serosal-to-mucosal apparent permeability (P(app)) to (3)H-5HT of rat jejunum, ileum and colon. In conclusion, human and rat SERT-mediated transport is inhibited by several distinct organic cations, some of which are therapeutic agents or drugs of abuse. Knowledge on which organic cations interfere with SERT-mediated transport of 5HT will have major implications in tissues where 5HT plays important physiological roles (eg. central nervous system, intestine and placenta).

Analysis of Variance↗

PubMed2004

Estimation of the human intestinal permeability of butyltin species using the Caco-2 cell line model.

The main objective of the work was the setup of the Caco-2 human intestinal cell-line model for the study of the intestinal permeation of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT). The study was focused in gathering information on (a) the relative permeability of butyltins, (b) their possible permeation routes (paracellular/transcellular) and (c) the eventual interactions between the different butyltins when occurring as a mixture. The presence of basolateral serum protein greatly influenced the permeability, causing a large net clearance, but the apparent permeability (Papp) values were comparable to that of phenolred, suggesting a low in vivo permeability of the butyltins. The found permeability pattern correlates well with the general in vivo toxicity pattern (trialkyltin>dialkyltin>>monoalkyltin). The accumulation pattern (DBT>TBT>MBT) was different from that of permeability and may be an important element regarding the elucidation of some specific strong toxic effects caused by the dialkyltins in several species. The transport of MBT and DBT was found to be dependent on the paracellular route status. An interaction between the butyltin compounds in a mixture was found for the accumulation results (the accumulation was significantly higher for the three compounds when in a mixture). A set of useful information about the butyltin accumulation and transport by the epithelial Caco-2 cell line was, thus, achieved, constituting a starting point for future research on the permeability of butyltins from contaminated food and beverages.

Biological Transport↗

PubMed2003

Uptake of 1-methyl-4-phenylpyridinium (MPP+) by the JAR human placental choriocarcinoma cell line: comparison with 5-hydroxytryptamine.

The aim of this work was to characterize the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) in the JAR human choriocarcinoma cell line. As JAR cells, as well as the placenta, express the neuronal serotonin transporter (SERT), a comparison between the uptake of (3)H-MPP(+) and (3)H-serotonin ((3)H-5HT) was made. Specific uptake of (3)H-MPP(+) (0.2 microM ) was temperature-, Na(+)- and potential-dependent. 5HT and MPP(+) reduced (3)H-MPP(+) specific uptake (for 5HT, its IC(50) was found to be 4 microM ). The SERT inhibitors desipramine and fluoxetine also inhibited (3)H-MPP(+) specific uptake (with IC(50)s of 189 and 0.92 microM, respectively). The inhibitors of the extraneuronal monoamine transporter (EMT) and of the organic cation transporter type 2 (OCT2), corticosterone and decynium22, had no effect on (3)H-MPP(+) specific uptake, but cyanine863 concentration-dependently reduced it (with an IC(50) of 23 microM ). Specific uptake of (3)H-5HT (0.2 microM ) by JAR cells was temperature-, Na(+)- and potential-dependent. 5HT, MPP(+), desipramine and fluoxetine concentration-dependently inhibited (3)H-5HT specific uptake (with IC(50)s of 1.9 microM, 50 microM, 0.17 microM and 0.046 microM, respectively). Corticosterone showed no effect, but decynium22 and cyanine863 significantly reduced(3) H-5HT specific uptake. For cyanine863, its IC(50) was found to be 11 microM. In conclusion, the results suggest that: (1) uptake of (3)H-5HT by JAR cells occurs exclusively through SERT; (2) uptake of(3) H-MPP(+) by JAR cells involves SERT and also another transporter; (3) neither EMT nor OCT2 are functionally present in JAR cells.

1-Methyl-4-phenylpyridinium↗

PubMed2003

An update on the extraneuronal monoamine transporter (EMT): characteristics, distribution and regulation.

Biological membranes prevent transmembrane diffusion in the majority of organic molecules that bear net charges at physiological pH. Consequently, these compounds must use more or less specific membrane-bound transport systems to be imported into or exported from cells or organisms. The extraneuronal monoamine transporter (EMT) is a transmembranar transport system involved in the transfer of monoamine compounds across cell membranes. It was identified more than 30 years ago [1], its functional characteristics being thereafter described [review by 2]. The recent cloning of this transporter in man and rat reopened investigation and interest in this entity. EMT is a Na(+) and Cl(-)-independent, potential-dependent carrier, known to have a broad tissue distribution (eg. myocardium, vascular and non-vascular smooth muscle cells, glandular cells, placenta and CNS glial cells). According to its transport function and primary structure, EMT is included in the amphiphilic solute facilitator (ASF) family of transporters. Physiological substrates for EMT include the monoamines serotonin, dopamine, noradrenaline, adrenaline and histamine. Moreover, several xenobiotics including the neurotoxin 1-methyl-4-phenylpyridinium, clonidine, cimetidine and the K(+)-channel blocker tetraethylammonium interact with this transporter. The aim of this work is to review knowledge concerning EMT, making an update on its functional characteristics, physiological importance and regulation. A special emphasis will be given to very recent investigations concerning regulation of EMT by intracellular second messenger systems and the interaction of modulators of P-glycoprotein, the product of the multidrug resistance gene MDR1, with EMT.

Animals↗

PubMed2002

Regulation of [(3)H]MPP(+) transport by phosphorylation/dephosphorylation pathways in RBE4 cells: role of ecto-alkaline phosphatase.

The aim of this study was to investigate the role of phosphorylation/dephosphorylation mechanisms at the blood-brain barrier (BBB) in the uptake of organic cations. The experiments were performed using RBE4 cells, an immortalized, rat brain microvessel endothelial cell line, an in vitro model of the BBB. The modulation of the uptake of 1-methyl-4-phenylpyridinium (MPP(+)), a model organic cation, at the apical membrane of RBE4 cells was studied. Agents that stimulate protein kinase A, but not protein kinase C, produced a moderate inhibition (approximately 18% reduction) of uptake of [(3)H]MPP(+) by RBE4 cells. Okadaic acid, an inhibitor of protein serine/threonine phosphatase, did not affect uptake of (3)H-MPP(+), but the alkaline phosphatase (ALP) inhibitor levamisole markedly reduced (3)H-MPP(+) uptake. The activity of membrane-bound ALP expressed on the apical surface of RBE4 cells was studied at pH 7.4 using p-nitrophenylphosphate as substrate. Kaempferol, progesterone, 3-isobutyl-1-methylxanthine, all- trans-retinoic acid and iron stimulated ecto-ALP activity and uptake of [(3)H]MPP(+) in RBE4. Orthovanadate (a protein tyrosine phosphatase inhibitor) markedly inhibited both ecto-ALP activity and uptake of [(3)H]MPP(+) by RBE4 cells. In conclusion, these results suggest that apical transporter(s) of MPP(+) in RBE4 cells may be under the control of phosphorylation/dephosphorylation mechanisms, being active in the dephosphorylated state. A physiological role for ALP in the modulation of organic cation transport in the BBB is suggested.

1-Methyl-4-phenylpyridinium↗

PubMed2002

Modulation of insulin transport in rat brain microvessel endothelial cells by an ecto-phosphatase activity.

The physiological function of alkaline phosphatase (ALP) remains controversial. It was recently suggested that this membrane-bound enzyme has a role in the modulation of transmembranar transport systems into hepatocytes and Caco-2 cells. ALP activity expressed on the apical surface of blood-brain barrier cells, and its relationship with (125)I-insulin internalization were investigated under physiological conditions using p-nitrophenylphosphate (p-NPP) as substrate. For this, an immortalized cell line of rat capillary cerebral endothelial cells (RBE4 cells) was used. ALP activity and (125)I-insulin internalization were evaluated in these cells. The results showed that RBE4 cells expressed ALP, characterized by an ecto-oriented active site which was functional at physiological pH. Orthovanadate (100 microM), an inhibitor of phosphatase activities, decreased both RBE4-ALP activity and (125)I-insulin internalization. In the presence of L-arginine (1 mM) or adenosine (100 microM) RBE4-ALP activity and (125)I-insulin, internalization were significantly reduced. However, D-arginine (1 mM) had no significant effect. Additionally, RBE4-ALP activity and (125)I-insulin internalization significantly increased in the presence of the bioflavonoid kaempferol (100 microM), of the phorbol ester PMA (80 nM), IBMX (1 mM), progesterone (200 microM and 100 microM), beta-estradiol (100 microM), iron (100 microM) or in the presence of all-trans retinoic acid (RA) (10 microM). The ALP inhibitor levamisole (500 microM) was able to reduce (125)I-insulin internalization to 69.1 +/- 7.1% of control. Our data showed a positive correlation between ecto-ALP activity and (125)I-insulin incorporation (r = 0.82; P < 0.0001) in cultured rat brain endothelial cells, suggesting that insulin entry into the blood-brain barrier may be modulated through ALP.

Animals↗

PubMed2002

Modulation of uptake of organic cationic drugs in cultured human colon adenocarcinoma Caco-2 cells by an ecto-alkaline phosphatase activity.

Alkaline phosphatase (ALP) refers to a group of nonspecific phosphomonoesterases located primarily in cell plasma membrane. It has been described in different cell lines that ecto-ALP is directly or indirectly involved in the modulation of organic cation transport. We aimed to investigate, in Caco-2 cells, a putative modulation of 1-methyl-4-phenylpyridinium (MPP(+)) apical uptake by an ecto-ALP activity. Ecto-ALP activity and (3)H-MPP(+) uptake were evaluated in intact Caco-2 cells (human colon adenocarcinoma cell line), in the absence and presence of a series of drugs. The activity of membrane-bound ecto-ALP expressed on the apical surface of Caco-2 cells was studied at physiological pH using p-nitrophenylphosphate as substrate. The results showed that Caco-2 cells express ALP activity, characterized by an ecto-oriented active site functional at physiological pH. Genistein (250 micro M), 3-isobutyl-1-methylxanthine (1 mM), verapamil (100 micro M), and ascorbic acid (1 mM) significantly increased ecto-ALP activity and decreased (3)H-MPP(+) apical transport in this cell line. Orthovanadate (100 micro M) showed no effect on (3)H-MPP(+) transport and on ecto-ALP activity. On the other hand, okadaic acid (310 nM) and all trans-retinoic acid (1 micro M) significantly increased (3)H-MPP(+) uptake and inhibited ecto-ALP activity. There is a negative correlation between the effect of drugs upon ecto-ALP activity and (3)H-MPP(+) apical transport (r = -0.9; P = 0.0014). We suggest that apical uptake of organic cations in Caco-2 cells is affected by phosphorylation/dephosphorylation mechanisms, and that ecto-ALP activity may be involved in this process.

Adenocarcinoma↗

PubMed2001

Effect of P-glycoprotein modulators on the human extraneuronal monoamine transporter.

The aim of this work was to investigate the effect of P-glycoprotein modulators on human extraneuronal monoamine transporter (EMT)-mediated transport. The experiments were performed using a cell line from human embryonic kidney (HEK293 cells) stably transfected with pcDNA3hEMT (293(hEMT)), or with pcDNA3 alone (293(control)). Of the P-glycoprotein modulators tested, rhodamine123, verapamil and daunomycin concentration-dependently inhibited EMT-mediated uptake of [3H]1-methyl-4-phenylpyridinium ([3H]MPP(+)). The corresponding IC(50)'s were found to be 3.6, 37 and 130 microM, respectively. By contrast, vinblastine, digitoxin and cyclosporine A were devoid of effect. The endogenous organic cation tyramine, but not choline, inhibited EMT-mediated transport (IC(50) of 468 microM). Moreover, L-arginine and L-histidine (up to 1 mM) did not affect [3H]MPP(+) uptake. Finally, MPP(+) and tyramine trans-stimulated [3H]MPP(+) uptake, but rhodamine123 had no effect, and verapamil and daunomycin trans-inhibited [3H]MPP(+) uptake. In conclusion, this study shows that several cationic modulators of P-glycoprotein inhibit EMT-mediated transport. As a consequence, the interaction of P-glycoprotein modulators with EMT must be taken into account, and the consequences of this interaction must not be forgotten when using such drugs in vivo.

1-Methyl-4-phenylpyridinium↗

PubMed2001

Transport of [3H]MPP+ in an immortalized rat brain microvessel endothelial cell line (RBE 4).

The aim of this study was to characterize the transport of the organic cation 1-methyl-4-phenylpyridinium (MPP+) in an immortalized cell line of rat capillary cerebral endothelial cells (RBE 4). Verapamil (100 microM) and rhodamine 123 (10 microM), and decynium22 (2 microM) and corticosterone (100 microM) reduced cellular accumulation of [3H]MPP+ applied from the luminal and abluminal cell border, respectively. When cells were grown on plastic supports, [3H]MPP+ accumulated in the cells. The kinetic parameters of the saturable component were: Km=25 microM and Vmax=246 pmol per mg protein and 15 min. A selective organic anion transport inhibitor and selective inhibitors of the L- and A-type amino acid transporters did not affect [3H]MPP+ uptake. Uptake of [3H]MPP+ was Na+-independent and metabolic energy-, pH- and potential-dependent. It was inhibited by several organic cations (e.g., verapamil, quinidine, daunomycin, dopamine) but not by others (cimetidine, tetraethylammonium, N-methylnicotinamide). In conclusion, [3H]MPP+ is efficiently transported by RBE 4 cells in both abluminal-to-luminal and luminal-to-abluminal directions. Absorption of [3H]MPP+ seems to occur through a carrier-mediated mechanism belonging to the amphiphilic solute facilitator (ASF) family of transporters, but distinct from the known members of this family.

1-Methyl-4-phenylpyridinium↗

PubMed2001

Apical uptake of organic cations by human intestinal Caco-2 cells: putative involvement of ASF transporters.

The aim of this work was to characterise the intestinal absorption of organic cations, by testing the possibility of involvement of known members of the amphiphilic solute facilitator (ASF) family in this process. For that purpose, the characteristics of the uptake of 1-methyl-4-phenylpyridinium, a model organic cation, at the brush-border membrane of Caco-2 cells were compared with those of the extraneuronal monoamine transporter (EMT)-mediated transport. Uptake of [3H]MPP+ by Caco-2 and 293hEMT cells showed pH-dependence: it was significantly reduced (to 86% and 62% of control, respectively) when the pH of the extracellular medium was decreased to 6.2, and increased (to 116% and 136% of control, respectively) when the extracellular pH was increased to 8.2. Uptake of [3H]MPP+ by Caco-2 cells and 293hEMT cells showed potential-dependence: substitution of KCl for NaCl in the incubation medium resulted in a reduction in the inward transport of [3H]MPP+ (to 70% and 40% of control, respectively). Uptake of [3H]MPP+ by Caco-2 and 293hEMT cells showed only little dependence on Na+: substitution of NaCl of the incubation media with LiCl resulted in a small decrease (of 19% and 14%, respectively) in [3H]MPP+ uptake. However, when NaCl was substituted with choline chloride, a significant reduction in [3H]MPP+ uptake by Caco-2 and 2931hEMT cells (of 56% and 68%, respectively) was observed. The effect of various compounds on initial rates of [3H]MPP+ uptake into Caco-2 and 293hEMT cells was tested. All compounds tested interacted with the specific [3H]MPP+ uptake in both cell lines. There was no correlation between the IC50s in relation to inhibition of [3H]MPP+ uptake into Caco-2 cells and into 293hEMT cells. Reverse transcriptase-polymerase chain reaction indicates that mRNA of hEMT and of the human organic cation transporter 1 (hOCT1) are present in Caco-2 cells. In conclusion, our results suggest that uptake of organic cations at the brush-border membrane of Caco-2 cells may occur through two distinct Na+-independent transporters belonging to the ASF family: hEMT and hOCT1.

1-Methyl-4-phenylpyridinium↗

PubMed2001

Regulation of human extraneuronal monoamine transporter (hEMT) expressed in HEK293 cells by intracellular second messenger systems.

Several transmembrane transporters of organic compounds are regulated by phosphorylation/dephosphorylation mechanisms. The aim of this study was to investigate the possible regulation of the human extraneuronal monoamine transporter, hEMT, by these mechanisms. The experiments were performed using HEK293 cells stably transfected with pcDNA3hEMT (293hEMT). The characteristics of hEMT-mediated uptake of [3H]1-methyl-4-phenylpyridinium ([3H]MPP+) were studied by incubating the cells at 37 degrees C for 1 min with 200 nM [3H]MPP+. Uptake of [3H]MPP+ by 293hEMT cells was not affected or only slightly reduced by modulators of protein kinase A, protein kinase C, or protein kinase G. It was not affected by an inhibitor of protein tyrosine kinase and was reduced by mitogen-activated protein kinase inhibitors. Uptake of [3H]MPP+ by 293hEMT cells was independent of extracellular Ca2+ and strongly reduced by Ca2+/calmodulin pathway inhibitors. Uptake of [3H]MPP+ by 293hEMT cells was strongly reduced in the presence of non-selective phosphodiesterase inhibitors (IBMX, caffeine, theophylline). The effect of IBMX was independent of extracellular Ca2+ its IC50 was found to be 82.0 microM (66.2-101.6 microM; n=4), and its inhibitory effect resulted from a significant decrease in the maximal velocity of [3H]MPP+ uptake, with no change in the Michaelis-Menten constant. [3H]MPP+ uptake was reduced by 8-methoxy-methyl-IBMX, a selective inhibitor of the Ca2+/calmodulin-dependent phosphodiesterase (PDE1), but not by zaprinast, a selective inhibitor of PDE5. Uptake of [3H]MPP+ by 293hEMT cells was strongly reduced by protein tyrosine phosphatase inhibitors, by an alkaline phosphatase inhibitor and, by contrast. showed an increase in the presence of exogenous alkaline phosphatase. In conclusion, these results suggest that hEMT is regulated by phosphorylation/dephosphorylation mechanisms, being active in the dephosphorylated state.

1-Methyl-4-phenylpyridinium↗

PubMed2000

Somatostatin inhibits the release of noradrenaline induced by electrical stimulation of the rat mesenteric artery.

Somatostatin, a peptide with antisecretory and antiproliferative effects, coexists with noradrenaline in sympathetic neurons. Octreotide, a stable somatostatin analogue, prevents hypertension and cardiovascular structural changes induced by prolonged infusion of DPSPX (1,3-dipropyl-8-sulfophenylxanthine, a non-selective adenosine receptor antagonist) in rats. In the present work we investigated the effect of somatostatin and its analogue octreotide on the release of [(3)H]noradrenaline from sympathetic nerves in the rat mesenteric artery. Rat mesenteric arteries were incubated for 60 min with [(3)H]noradrenaline (0.2 microm), mounted in perifusion chambers, washed out for 90 min and electrically stimulated (2 Hz, 5 min, 50 mA). Radioactivity was measured in the tissue and in the perifusion fluid before, during and after stimulation. Both somatostatin and octreotide inhibited tritium release evoked by electrical stimulation of in vitro preparations of rat mesenteric arteries preloaded with [(3)H]noradrenaline. The maximal effects produced by octreotide and somatostatin were a 56 and 70% inhibition of noradrenaline release, respectively. For somatostatin an EC(50)=0. 18 n m (0.01 n m-2.2 n m;n =16) was calculated. When used alone, the somatostatin receptor antagonist, cyclo(7-aminoheptanoyl-Phe- d -Trp-Lys-Thr[BZL]) (CYCAM; 1 microm), had no effect on noradrenaline release induced by electrical stimulation. However, it was able to significantly antagonize the inhibitory effects of octreotide and somatostatin. These results are compatible with a negative modulatory role of somatostatin on sympathetic neurotransmission.

Animals↗

PubMed2000

Characterization of the transport of the organic cation [3H]MPP+ in human intestinal epithelial (Caco-2) cells.

The aim of this study was to characterize the transport of organic cations at the intestinal level, by studying the characteristics of the transport of 1-methyl-4-phenylpyridinium (MPP+) in Caco-2 cells. Transepithelial flux as well as cellular accumulation of [3H]MPP+ were quantitatively similar when substrate was applied from the basolateral or apical cell membrane. Verapamil (100 microM) and rhodamine123 (10 microM) significantly reduced [3H]MPP+ transepithelial flux in the apical-to-basolateral direction. When cells were grown on plastic supports, [3H]MPP+ was rapidly accumulated in the cells, both by saturable and nonsaturable mechanisms. The kinetic parameters of the saturable component were: Km: 449 microM and Vmax: 2,249 pmol per mg protein and 5 min. Uptake of [3H]MPP+ was metabolic energy-dependent and Na+-, pH- and potential-independent. It was inhibited by several organic cations (verapamil, rhodamine123, daunomycin, vinblastine, tetrabutylammonium and vecuronium) but not by others (tetraethylammonium and N-methylnicotinamide). Decynium22 and corticosterone inhibited [3H]MPP+ uptake into the cells. The P-glycoprotein antibody UIC2 (20 microg/ml) had no effect. In conclusion, [3H]MPP+ is efficiently transported by Caco-2 cells in both basolateral-to-apical (secretion) and apical-to-basolateral (absorption) directions. Absorption of [3H]MPP+ at the apical membrane seems to occur through a carrier-mediated mechanism belonging to the Amphiphilic Solute Facilitator (ASF) family of transporters, but distinct from the known members of this family.

1-Methyl-4-phenylpyridinium↗

PubMed2000

Differences between duodenal and jejunal rat alkaline phosphatase.

OBJECTIVES: The aim of this study was to kinetically characterize rat tissue-nonspecific-alkaline phosphatase (TNS-ALP) and intestinal (duodenal- and jejunal-IALP), and to determine the effect of substances known to affect phosphorylation/dephosphorylation on TNS- and IALP activity. DESIGN AND RESULTS: The ranking order of ALP activity (K(enzyme)) was duodenal mucosa (IALP) > jejunal mucosa (IALP) > kidney (TNS-ALP) > brain (TNS-ALP). Levamisole was found to produce a concentration-dependent decrease of ALP activity in kidney and brain. However, levamisole had no effect on duodenal ALP activity and produced a concentration-dependent increase on jejunum ALP activity. In brain and jejunum homogenates, octreotide, a stable somatostatin analogue, produced a concentration-dependent increase in ALP activity. In relation to duodenum ALP activity, octreotide produced a biphasic effect.Reverse transcription-polymerase chain reaction showed the presence of IALP-I mRNA both in duodenal and jejunal mucosa, but IALP-II only in duodenal mucosa. CONCLUSIONS: The results show that duodenal- and jejunal-IALP differ in kinetic parameters and in drug sensitivity. Thus, we can speculate on a different physiologic role for duodenal- and jejunal-IALP, particularly in relation to their dephosphorylation targets.

Adjuvants, Immunologic↗