Mechanosensitive Pannexin 1 Activity Is Modulated by Stomatin in Human Red Blood Cells.

Pannexin 1 (PANX1) was proposed to drive ATP release from red blood cells (RBCs) in response to stress conditions. Stomatin, a membrane protein regulating mechanosensitive channels, has been proposed to modulate PANX1 activity in non-erythroid cells. To determine whether stomatin modulates PANX1 activity in an erythroid context, we have (i) assessed the in situ stomatin-PANX1 interaction in RBCs, (ii) measured PANX1-stimulated activity in RBCs expressing stomatin or from OverHydrated Hereditary Stomatocytosis (OHSt) patients lacking stomatin, and in erythroid K562 cells invalidated for stomatin. Proximity Ligation Assay coupled with flow imaging shows 27.09% and 6.13% positive events in control and OHSt RBCs, respectively. The uptake of dyes 5(6)-Carboxyfluorescein (CF) and TO-PRO-3 was used to evaluate PANX1 activity. RBC permeability for CF is 34% and 11.8% in control and OHSt RBCs, respectively. PANX1 permeability for TO-PRO-3 is 35.72% and 18.42% in K562 stom+ and stom- clones, respectively. These results suggest an interaction between PANX1 and stomatin in human RBCs and show a significant defect in PANX1 activity in the absence of stomatin. Based on these results, we propose that stomatin plays a major role in opening the PANX1 pore by being involved in a caspase-independent lifting of autoinhibition.

Human erythrocytes release ATP by a novel pathway involving VDAC oligomerization independent of pannexin-1.

We previously demonstrated that the translocase protein TSPO2 together with the voltage-dependent anion channel (VDAC) and adenine nucleotide transporter (ANT) were involved in a membrane transport complex in human red blood cells (RBCs). Because VDAC was proposed as a channel mediating ATP release in RBCs, we used TSPO ligands together with VDAC and ANT inhibitors to test this hypothesis. ATP release was activated by TSPO ligands, and blocked by inhibitors of VDAC and ANT, while it was insensitive to pannexin-1 blockers. TSPO ligand increased extracellular ATP (ATPe) concentration by 24-59% over the basal values, displaying an acute increase in [ATPe] to a maximal value, which remained constant thereafter. ATPe kinetics were compatible with VDAC mediating a fast but transient ATP efflux. ATP release was strongly inhibited by PKC and PKA inhibitors as well as by depleting intracellular cAMP or extracellular Ca2+, suggesting a mechanism involving protein kinases. TSPO ligands favoured VDAC polymerization yielding significantly higher densities of oligomeric bands than in unstimulated cells. Polymerization was partially inhibited by decreasing Ca2+ and cAMP contents. The present results show that TSPO ligands induce polymerization of VDAC, coupled to activation of ATP release by a supramolecular complex involving VDAC, TSPO2 and ANT.

Recombinant Overexpression of Mammalian TSPO Isoforms 1 and 2.

TSPO is a 18 kDa membrane protein that exists in mammalian as two isoforms 1 and 2. They are involved in different functions and are located in different membranes. TSPO1 is mainly located in outer mitochondrial membrane, whereas TSPO2 is encountered in plasma membrane of red blood cells. Determination of their structures is a milestone to understand their function. Their natural abundance is not sufficient to get large amounts usually required for structural studies. We described heterologous overexpression in both bacterial and cell-free system and purification on immobilized-metal affinity chromatography (IMAC) of both proteins. Using the same vector, TSPO1 is mostly recovered in bacterial inclusion bodies whereas TSPO2 is found in both bacterial cytosol and inclusion bodies, but in low amounts. Cell-free expression was the best system to overexpress pure TSPO2.

Dynamic regulation of extracellular ATP in Escherichia coli.

We studied the kinetics of extracellular ATP (ATPe) in Escherichia coli and their outer membrane vesicles (OMVs) stimulated with amphipatic peptides melittin (MEL) and mastoparan 7 (MST7). Real-time luminometry was used to measure ATPe kinetics, ATP release, and ATPase activity. The latter was also determined by following [32P]Pi released from [γ-32P]ATP. E. coli was studied alone, co-incubated with Caco-2 cells, or in rat jejunum segments. In E. coli, the addition of [γ-32P]ATP led to the uptake and subsequent hydrolysis of ATPe. Exposure to peptides caused an acute 3-fold (MST7) and 7-fold (MEL) increase in [ATPe]. In OMVs, ATPase activity increased linearly with [ATPe] (0.1-1 µM). Exposure to MST7 and MEL enhanced ATP release by 3-7 fold, with similar kinetics to that of bacteria. In Caco-2 cells, the addition of ATP to the apical domain led to a steep [ATPe] increase to a maximum, with subsequent ATPase activity. The addition of bacterial suspensions led to a 6-7 fold increase in [ATPe], followed by an acute decrease. In perfused jejunum segments, exposure to E. coli increased luminal ATP 2 fold. ATPe regulation of E. coli depends on the balance between ATPase activity and ATP release. This balance can be altered by OMVs, which display their own capacity to regulate ATPe. E. coli can activate ATP release from Caco-2 cells and intestinal segments, a response which in vivo might lead to intestinal release of ATP from the gut lumen.

Distribution, pharmacological characterization and function of the 18 kDa translocator protein in rat small intestine.

BACKGROUND INFORMATION: The TSPO (18 kDa translocator protein) is a mitochondrial transmembrane protein involved in cholesterol transport in organs that synthesize steroids and bile salts. Different natural and synthetic high-affinity TSPO ligands have been characterized through their ability to stimulate cholesterol transport, but also to stimulate other physiological functions including cell proliferation, apoptosis and calcium-dependent transepithelial ion secretion. Here, we investigate the localization and functions of TSPO in the small intestine. RESULTS: TSPO was present in enterocyte mitochondria but not in rat intestinal goblet cells. Enterocyte cytoplasm also contained the endogenous TSPO ligand, polypeptide DBI (diazepam-binding inhibitor). Whereas intestinal TSPO had high affinity for the synthetic ligand PK 11195, the pharmacological profile of TSPO in the duodenum was distinct from the jejunum and ileum. Specifically, benzodiazepine Ro5-4864 and protoporphyrin IX showed 5-13-fold lower affinity for duodenal TSPO. The mRNA and protein ratios of TSPO to other mitochondrial membrane proteins VDAC (voltage-dependent anion channel) and ANT (adenine nucleotide transporter) were significantly different. PK 11195 stimulated calcium-dependent chloride secretion in the duodenum and calcium-dependent chloride absorption in the ileum, but did not affect jejunum ion transport. CONCLUSIONS: The functional differences in subpopulations of TSPO in different regions of the intestine could be related to structural organization of mitochondrial protein complexes that mediate the ability of TSPO to modulate either chloride secretion or absorption in the duodenum and ileum respectively.

Modulation by thyroid hormones of rat parotid amylase secretion stimulated by 5-hydroxytryptamine.

The effects of 5-hydroxytryptamine (5-HT) upon amylase secretion by rat parotid glands were studied in three groups of animals: (a) intact control rats (euthyroid rats); (b) hypothyroid rats obtained by surgical thyroidectomy 2 wk before the experiments; and (c) hyperthyroid rats obtained by the administration of sodium l-triiodothyronine for 2 wk before the experiments. Hyperthyroid rats showed significantly higher baseline amylase release than control rats. When the glands were stimulated with 5-HT (30 micro m), amylase release was significantly lower in the hypothyroid group and higher in the hyperthyroid rats than in control group. Addition of cholinergic, adrenergic or substance P antagonists did not modify 5-HT-stimulated amylase activity. The effects of 5-HT were partly but significantly blocked by the addition of 10 micro m methysergide (HT1/2/7 receptor blocker) in the three groups of rats. In contrast, 10 micro m ketanserine (HT2A receptor blocker) partly blocked the response to 5-HT only in the hyperthyroid animals. It was concluded that 5-HT induces amylase secretion by rat parotid glands through specific serotoninergic receptors, and that thyroid status modulates the 5-HT effect.

Sialoquímica en el síndrome de SjIgren : nuevo índice para el diagnóstico / Sialochemistry in the SjIgrens syndrome : new index for the diagnosis

El síndrome de SjIgren (SS) está caracterizado por una inflamación crónica de las glándulas lagrimales y salivales con infiltración linfocitaria, provocando sequedad ocular y bucal. Además de la disminución del flujo salival se han observado alteraciones en diversos parámetros bioquímicos de la saliva. El objetivo del presente trabajo consistió en evaluar la sialometría basal (saliva total) y estimulada (saliva parotídea), y cuantificar diversos parámetros sialoquímicos en 62 pacientes con SS y 28 pacientes controles, con el fin de clarificar su aptitud diagnóstica. La sialometría basal tomada en forma temporal (7 meses) en algunos pacientes, demostró ser efectiva sólo para la evaluación de la xerostomía y evidenció la existencia de picos esporádicos de secreción. La saliva parotídea estimulada presentó una disminución del flujo (0.89ñ0.09 vs. 0.48ñ0.06 mL/min.), amilasa (602.40ñ76.70 vs. 436.10ñ53.80 AU), y proteínas totales (152.04ñ9.80 vs. 116.50ñ8.30 mg/dL), y un aumento de las concentraciones de Na+(22.75ñ3.52 vs. 43.46ñ3.22 mEq/L), e IgG (0.40ñ0.13 vs. 3.91ñ1.01 mg/dL) y/o IgM (0.40ñ0.12 vs. 1.54ñ0.31 mg/dL). No en todos los pacientes se registró un aumento simultáneo de IgG e IgM, pero siempre apareció elevada una de ellas. Como el índice salival que resulta del producto de las concentraciones de IgG por IgM es siempre mayor a 0.25 en los pacientes con SS, y menor o igual a este valor en el grupo control, creemos que, sumado al carácter no invasivo del método de extracción, sería una herramienta complementaria de gran utilidad en el diagnóstico de este síndrome. (AU)

Sialoquímica en el síndrome de SjÖgren : nuevo índice para el diagnóstico / Sialochemistry in the SjÖgren's syndrome : new index for the diagnosis

El síndrome de SjÖgren (SS) está caracterizado por una inflamación crónica de las glándulas lagrimales y salivales con infiltración linfocitaria, provocando sequedad ocular y bucal. Además de la disminución del flujo salival se han observado alteraciones en diversos parámetros bioquímicos de la saliva. El objetivo del presente trabajo consistió en evaluar la sialometría basal (saliva total) y estimulada (saliva parotídea), y cuantificar diversos parámetros sialoquímicos en 62 pacientes con SS y 28 pacientes controles, con el fin de clarificar su aptitud diagnóstica. La sialometría basal tomada en forma temporal (7 meses) en algunos pacientes, demostró ser efectiva sólo para la evaluación de la xerostomía y evidenció la existencia de picos esporádicos de secreción. La saliva parotídea estimulada presentó una disminución del flujo (0.89ñ0.09 vs. 0.48ñ0.06 mL/min.), amilasa (602.40ñ76.70 vs. 436.10ñ53.80 AU), y proteínas totales (152.04ñ9.80 vs. 116.50ñ8.30 mg/dL), y un aumento de las concentraciones de Na+(22.75ñ3.52 vs. 43.46ñ3.22 mEq/L), e IgG (0.40ñ0.13 vs. 3.91ñ1.01 mg/dL) y/o IgM (0.40ñ0.12 vs. 1.54ñ0.31 mg/dL). No en todos los pacientes se registró un aumento simultáneo de IgG e IgM, pero siempre apareció elevada una de ellas. Como el índice salival que resulta del producto de las concentraciones de IgG por IgM es siempre mayor a 0.25 en los pacientes con SS, y menor o igual a este valor en el grupo control, creemos que, sumado al carácter no invasivo del método de extracción, sería una herramienta complementaria de gran utilidad en el diagnóstico de este síndrome.