Non-selective cation channel activity of aquaporin AtPIP2;1 regulated by Ca2+ and pH.

The aquaporin AtPIP2;1 is an abundant plasma membrane intrinsic protein in Arabidopsis thaliana that is implicated in stomatal closure, and is highly expressed in plasma membranes of root epidermal cells. When expressed in Xenopus laevis oocytes, AtPIP2;1 increased water permeability and induced a non-selective cation conductance mainly associated with Na+ . A mutation in the water pore, G103W, prevented both the ionic conductance and water permeability of PIP2;1. Co-expression of AtPIP2;1 with AtPIP1;2 increased water permeability but abolished the ionic conductance. AtPIP2;2 (93% identical to AtPIP2;1) similarly increased water permeability but not ionic conductance. The ionic conductance was inhibited by the application of extracellular Ca2+ and Cd2+ , with Ca2+ giving a biphasic dose-response with a prominent IC50 of 0.32 mм comparable with a previous report of Ca2+ sensitivity of a non-selective cation channel (NSCC) in Arabidopsis root protoplasts. Low external pH also inhibited ionic conductance (IC50 pH 6.8). Xenopus oocytes and Saccharomyces cerevisiae expressing AtPIP2;1 accumulated more Na+ than controls. Establishing whether AtPIP2;1 has dual ion and water permeability in planta will be important in understanding the roles of this aquaporin and if AtPIP2;1 is a candidate for a previously reported NSCC responsible for Ca2+ and pH sensitive Na+ entry into roots.

Mechanism and functional impact of CD40 ligand-induced von Willebrand factor release from endothelial cells.

Co-stimulation via CD154 binding to CD40, pivotal for both innate and adaptive immunity, may also link haemostasis to vascular remodelling. Here we demonstrate that human platelet-bound or recombinant soluble CD154 (sCD154) elicit the release from and tethering of ultra-large (UL) von Willebrand factor (vWF) multimers to the surface of human cultured endothelial cells (ECs) exposed to shear stress. This CD40-mediated ULVWF multimer release from the Weibel-Palade bodies was triggered by consecutive activation of TRAF6, the tyrosine kinase c-Src and phospholipase Cγ1 followed by inositol-1,4,5 trisphosphate-mediated calcium mobilisation. Subsequent exposure to human washed platelets caused ULVWF multimer-platelet string formation on the EC surface in a shear stress-dependent manner. Platelets tethered to these ULVWF multimers exhibited P-selectin on their surface and captured labelled monocytes from the superfusate. When exposed to shear stress and sCD154, native ECs from wild-type but not CD40 or vWF-deficient mice revealed a comparable release of ULVWF multimers to which murine washed platelets rapidly adhered, turning P-selectin-positive and subsequently capturing monocytes from the perfusate. This novel CD154-provoked ULVWF multimer-platelet string formation at normal to fast flow may contribute to vascular remodelling processes requiring the perivascular or intravascular accumulation of pro-inflammatory macrophages such as arteriogenesis or atherosclerosis.

Quantitative assessment of visceral fat in morbidly obese patients by means of wide-bore MRI and its relation to lower esophageal sphincter pressure and signs of gastroesophageal reflux.

BACKGROUND: The aim of this study was to quantitatively assess visceral adipose tissue (VAT) by means of a wide-bore MR scanner in a cohort of morbidly obese patients referred for bariatric surgery. Furthermore, it was investigated whether gastroesophageal reflux disease (GERD) and lower esophageal sphincter pressure (LESP) are related to the volume of visceral fat masses. METHODS: Twenty-five morbidly obese patients (nine male, 16 female) were prospectively enrolled. In addition to common anthropometric measures of obesity, VAT was determined quantitatively by multi-slice MRI. Symptoms of GERD were evaluated using a standardized questionnaire, while endoscopy of the upper gastrointestinal tract was performed to reveal pathologies of the gastroesophageal junction. LESP was evaluated by esophageal manometry. RESULTS: Study population showed a body mass index (BMI) between 35.2 and 59.1 kg/m(2). Waist-to-hip ratio and VAT were significantly higher (p < 0.0001; p = 0.0021) in males (1.05 +/- 0.05; 8.89 +/- 2.33 l) than in females (0.86 +/- 0.07; 6.04 +/- 1.28 l). VAT was not correlated to BMI. LESP values and GERD-related symptoms were neither dependent on anthropometric measures nor on VAT in our cohort. CONCLUSIONS: VAT did not show a positive correlation with BMI in our cohort of extremely obese subjects, indicating a pronounced fat deposition in subcutaneous tissue compartment. Moreover, this indicates that VAT is limited to a gender-dependent maximum volume for each individual and seems to be no further increasing in extremely obese subjects. This might be the reason that neither symptoms nor endoscopic findings of GERD nor LESP were significantly influenced by the stage of morbid obesity.