Compensatory regulation of the sodium/phosphate cotransporters NaPi-IIc (SCL34A3) and Pit-2 (SLC20A2) during Pi deprivation and acidosis.
ABSTRACT The role of four Pi transporters in the renal handling of Pi was analyzed using functional and molecular methods. The abundance of NaPi-IIa, NaPi-IIc, and Pit-2 was increased by 100% in kidney from rats on a 0.1% Pi diet, compared to a 0.6% Pi diet. Pit-1 was not modified. Type II-mediated Pi uptake in Xenopus oocytes increased as the pH of the uptake medium increased, and the opposite occurred with Pit-1 and Pit-2. At pH 6.0, Pi uptake mediated through type II was approximately 10% of the uptake at pH 7.5, but the uptake through Pit-2 was 250% of the activity at pH 7.5. Real brush-border membrane vesicles (BBMV) responded to pH changes following the same pattern as type II transporters. Adaptation to a 0.1% Pi diet was accompanied by a 65% increase in the V (max) of BBMV Pi transport at pH 7.5, compared to a 0.6% Pi diet. The increase was only 11% at pH 6.0. Metabolic acidosis increased the expression of NaPi-IIc and Pit-2 in animals adapted to a low Pi diet, and phosphaturia was only observed in control diet animals. The combination of the pH effect, Pi adaptation, and metabolic acidosis suggests very modest involvement of Pit-2 in renal Pi handling. Real-time PCR and mathematical analyses of transport findings suggest that NaPi-IIa RNA accounts for 95% of all Pi transporters and that type II handles 97% of Pi transport at pH 7.5 and 60% of Pi transport at pH 6.0, depending on the pH and the physiological conditions.
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ABSTRACT: Intestinal phosphate (Pi) absorption across the apical membrane of small intestinal epithelial cells is mainly mediated by the type IIb Na-coupled phosphate co-transporter (NaPi-IIb), but its expression and regulation in the chicken remain unclear. In the present study, we investigated the mRNA and protein levels of NaPi-IIb in three regions of chicken small intestine, and related their expression levels to the rate of net phosphate absorption. Our results showed that maximal phosphate absorption occurs in the jejunum, however the highest expression levels of NaPi-IIb mRNA and protein occurs in the duodenum. In response to a low-Pi diet (TP 0.2%), there is an adaptive response restricted to the duodenum, with increased brush border membrane (BBM) Na-Pi transport activity and NaPi-IIb protein and mRNA abundance. However, when switched from a low- (TP 0.2%) to a normal diet (TP 0.6%) for 4 h, there is an increase in BBM NaPi-IIb protein abundance in the jejunum, but no changes in BBM NaPi-IIb mRNA. Therefore, our study indicates that Na-Pi transport activity and NaPi-IIb protein expression are differentially regulated in the duodenum vs the jejunum in the chicken.Asian Australasian Journal of Animal Sciences 10/2012; 25(10):1457-65. DOI:10.5713/ajas.2012.12187 · 0.56 Impact Factor
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ABSTRACT: The calibration of monolithic multi-junction (MJ) solar cells places high demands on the measurement setup. There exists a strong dependence of the I-V parameters on the incident spectrum. In this paper the influence of the high intensity simulator spectrum on the calibration of MJ concentrator cells is investigated taking a Ga<sub>0.35</sub>In<sub>0.65</sub>P/Ga<sub>0.83</sub>In<sub>0.17</sub>As dual-junction cell as example. It is shown that an unmatched simulator spectrum leads to an overestimation of the efficiency for the investigated dual-junction cell. Furthermore we observed different fill factor versus concentration behavior depending on which subcell is current limiting, probably caused by distributed series resistance effects. Finally, it is shown that the measured fill factor can serve as an indicator to identify whether an appropriate spectrum was used for the calibration under high illumination intensity.Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE; 06/2002
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ABSTRACT: Consensus standards for determining the efficiency of a concentrator cell or module have not been developed. NREL, Sandia National Laboratory, the Fraunhofer Institute for Solar Energy in Germany, and the Progress in Photovoltaics Efficiency Table authors have informally agreed upon concentrator-cell reference conditions. These conditions are 25°C cell temperature, 1-sun = 1000 W/m<sup>2</sup> total irradiance, and the ASTM E891-87 direct-normal reference spectrum. Deficiencies in the direct reference spectrum are discussed, and a more representative reference spectrum for evaluating concentrator cells is proposed. The spectrum was generated by the SMARTS model, and the atmospheric parameters are as close as possible to the existing direct spectrum, with the exception that the aerosol optical depth at 500 nm is reduced from 0.27 to 0.085.Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE; 06/2002