An outwardly rectifying chloride channel in BeWo choriocarcinoma cell line

Glyburide treatment in gestational diabetes is associated with increased placental glucose transporter 1 expression and higher birth weight

Use of glyburide in gestational diabetes (GDM) has raised concerns about fetal and neonatal side effects, including increased birth weight. Placental nutrient transport is a key determinant of fetal growth, however the effect of glyburide on placental nutrient transporters is largely unknown. We hypothesized that glyburide treatment in GDM pregnancies is associated with increased expression of nutrient transporters in the syncytiotrophoblast plasma membranes. We collected placentas from GDM pregnancies who delivered at term and were treated with either diet modification (n = 15) or glyburide (n = 8). Syncytiotrophoblast microvillous (MVM) and basal (BM) plasma membranes were isolated and expression of glucose (glucose transporter 1; GLUT1), amino acid (sodium-coupled neutral amino acid transporter 2; SNAT2 and L-type amino acid transporter 1; LAT1) and fatty acid (fatty acid translocase; FAT/CD36, fatty acid transporter 2 and 4; FATP2, FATP4) transporters was determined by Western blot. Additionally, we determined GLUT1 expression by confocal microscopy in cultured primary human trophoblasts (PHT) after exposure to glyburide. Birth weight was higher in the glyburide-treated group as compared to diet-treated GDM women (3764 ± 126 g vs. 3386 ± 75 g; p < 0.05). GLUT1 expression was increased in both MVM (+50%; p < 0.01) and BM (+75%; p < 0.01). In contrast, MVM FAT/CD36 (-65%; p = 0.01) and FATP2 (-65%; p = 0.02) protein expression was reduced in mothers treated with glyburide. Glyburide increased membrane expression of GLUT1 in a dose-dependent manner in cultured PHT. This data is the first to show that glyburide increases GLUT1 expression in syncytiotrophoblast MVM and BM in GDM pregnancies, and may promote transplacental glucose delivery contributing to fetal overgrowth.

Enhancement of an outwardly rectifying chloride channel in hippocampal pyramidal neurons after cerebral ischemia

Cerebral ischemia induces delayed, selective neuronal death in the CA1 region of the hippocampus. The underlying molecular mechanisms remain unclear, but it is known that apoptosis is involved in this process. Chloride efflux has been implicated in the progression of apoptosis in various cell types. Using both the inside-out and whole-cell configurations of the patch-clamp technique, the present study characterized an outwardly rectifying chloride channel (ORCC) in acutely dissociated pyramid neurons in the hippocampus of adult rats. The channel had a nonlinear current-voltage relationship with a conductance of 42.26±1.2pS in the positive voltage range and 18.23±0.96pS in the negative voltage range, indicating an outward rectification pattern. The channel is Cl(-) selective, and the open probability is voltage-dependent. It can be blocked by the classical Cl(-) channel blockers DIDS, SITS, NPPB and glibenclamide. We examined the different changes in ORCC activity in CA1 and CA3 pyramidal neurons at 6, 24 and 48h after transient forebrain ischemia. In the vulnerable CA1 neurons, ORCC activity was persistently enhanced after ischemic insult, whereas in the invulnerable CA3 neurons, no significant changes occurred. Further analysis of channel kinetics suggested that multiple openings are a major contributor to the increase in channel activity after ischemia. Pharmacological blockade of the ORCC partly attenuated cell death in the hippocampal neurons. We propose that the enhanced activity of ORCC might contribute to selective neuronal damage in the CA1 region after cerebral ischemia, and that ORCC may be a therapeutic target against ischemia-induced cell death.

Opening up of plasmalemma type-1 VDAC to form apoptotic "find me signal" pathways is essential in early apoptosis - evidence from the pathogenesis of cystic fibrosis resulting from failure of apoptotic cell clearance followed by sterile inflammation

Cell membrane-standing type-1 VDAC is involved in cell volume regulation and thus apoptosis. The channel has been shown to figure as a pathway for osmolytes of varying classes, ATP included. An early event in apoptotic cell death is the release of "find me signals" by cells that enter the apoptotic process. ATP is one of those signals. Apoptotic cells this way attract phagocytes for an immunologically silent cell clearance. Thus, whenever apoptosis fails by a blockade of plasmalemma type-1 VDAC processes of sterile inflammation must be assumed for cell elimination. This is evident from a close look on the pathogenetic process of cystic fibrosis (CF). However, in normal airway epithelia two different anion channels cooperate to guarantee an appropriate volume of airway surface liquid (ASL) necessary for surface clearing: the cystic fibrosis conductance regulator (CFTR) and the outwardly rectifying chloride channel (ORCC) complex also called "alternate chloride channel" and under the control of the CFTR. There are arguments, that type-1 VDAC forms the channel part of the ORCC complex, and it has been shown that CFTR and type-1 VDAC co-localize in the apical membranes of human surface respiratory epithelium. In cystic fibrosis, the central cAMP-dependent regulation of ion and water transport via functional CFTR is lost. Here, CFTR molecules do not reach the apical membranes of airway epithelia anymore or work in an insufficient way, respectively. In addition, type-1 VDAC is no longer available to work as a "find me signal" pathway. In consequence, clearing away of apoptotic cells is blocked. There are experimental data on the channel characteristics of type-1 VDAC under the anion channel blocker DIDS (4,4-diisothiocyanato-stilbenedisulphonic acid) that argue in favor of this hypothesis. Together, type-1 VDAC should be kept as a "find me signal" pathway, which may give way to several classes of such signals.

The migratory capacity of human trophoblastic BeWo cells: effects of aldosterone and the epithelial sodium channel

Aldosterone is a key regulator of the epithelial sodium channel (ENaC) and stimulates protein methylation on the β-subunit of the ENaC. We found that aldosterone (100 nM) promotes cellular migration in a wound-healing model in trophoblastic BeWo cells. Here, we tested if the positive influence of aldosterone on wound healing is related to methylation reactions. Cell migration and proliferation were measured in BeWo cells at 6 h, when mitosis is still scarce. Cell migration covered 12.4, 25.3, 19.6 and 45.1 % of the wound when cultivated under control, aldosterone (12 h), 8Br-cAMP and aldosterone plus 8Br-cAMP, respectively. Amiloride blocked the effects of aldosterone alone or in the presence of 8Br-cAMP on wound healing. Wound healing decreased in aldosterone (plus 8Br-cAMP) coexposed with the methylation inhibitor 3-deaza-adenosine (3-DZA, 12.9 % reinvasion of the wound). There was an increase in wound healing in aldosterone-, 8Br-cAMP- and 3-DZA-treated cells in the presence of AdoMet, a methyl donor, compared to cells in the absence of AdoMet (27.3 and 12.9 % reinvasion of the wound, respectively). Cell proliferation assessed with the reagent MTT was not changed in any of these treatments, suggesting that cellular migration is the main factor for reinvasion of wound healing. Electrophysiological studies showed an increase in ENaC current in the presence of aldosterone. This effect was higher with 8Br-cAMP, and there was a decrease when 3-DZA was present. AdoMet treatment partially reversed this phenomenon. We suggest that aldosterone positively influences wound healing in BeWo cells, at least in part through methylation of the ENaC.