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Extracellular Cl (extracellular + cl)
Selected AbstractsMercury compounds disrupt neuronal glutamate transport in cultured mouse cerebellar granule cellsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 4 2005Elena Fonfría Abstract Cerebellar granule cells are targeted selectively by mercury compounds in vivo. Despite the affinity of mercury for thiol groups present in all cells, the molecular determinant(s) of selective cerebellar degeneration remain to be elucidated fully. We studied the effect of mercury compounds on neuronal glutamate transport in primary cultures of mouse cerebellar granule cells. Immunoblots probed with an antibody against the excitatory amino acid transporter (EAAT) neuronal glutamate transporter, EAAT3, revealed the presence of a specific band in control and mercury-treated cultures. Micromolar concentrations of both methylmercury and mercuric chloride increased the release of endogenous glutamate, inhibited glutamate uptake, reduced mitochondrial activity, and decreased ATP levels. All these effects were completely prevented by the nonpermeant reducing agent Tris-(2-carboxyethyl)phosphine (TCEP). Reduction of mitochondrial activity by mercuric chloride, but not by methylmercury, was inhibited significantly by 4,4,-diisothiocyanato-stilbene-2,2,-disulfonic acid (DIDS) and by reduced extracellular Cl, ion concentration. In addition, DIDS and low extracellular Cl, completely inhibited the release of glutamate induced by mercuric chloride, and produced a partial although significant reduction of that induced by methylmercury. We suggest that a direct inhibition of glutamate uptake triggers an imbalance in cell homeostasis, leading to neuronal failure and Cl, -regulated cellular glutamate efflux. Our results demonstrate that neuronal glutamate transport is a novel target to be taken into account when assessing mercury-induced neurotoxicity. © 2005 Wiley-Liss, Inc. [source] Interaction of the Halobacterial Transducer to a Halorhodopsin Mutant Engineered so as to Bind the Transducer: Cl, Circulation Within the Extracellular Channel,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2007Chisa Hasegawa An alkali-halophilic archaeum, Natronomonas pharaonis, contains two rhodopsins that are halorhodopsin (phR), a light-driven inward Cl, pump and phoborhodopsin (ppR), the receptor of negative phototaxis functioning by forming a signaling complex with a transducer, pHtrII (Sudo Y. et al., J. Mol. Biol. 357 [2006] 1274). Previously, we reported that the phR double mutant, P240T/F250YphR, can bind with pHtrII. This mutant itself can transport Cl,, while the net transport was stopped upon formation of the complex. The flash-photolysis data were analyzed by a scheme in which phR,P1,P2,P3,P4,phR. The P3 of the wild-type and the double mutant contained two components, X- and O-intermediates. After the complex formation, however, the P3 of the double mutant lacked the X-intermediate. These observations imply that the X-intermediate (probably the N-intermediate) is the state having Cl, in the cytoplasmic binding site and that the complex undergoes an extracellular Cl, circulation because of the inhibition of formation of the X-intermediate. [source] Species differences in Cl, affinity and in electrogenicity of SLC26A6-mediated oxalate/Cl, exchange correlate with the distinct human and mouse susceptibilities to nephrolithiasisTHE JOURNAL OF PHYSIOLOGY, Issue 5 2008Jeffrey S. Clark The mouse is refractory to lithogenic agents active in rats and humans, and so has been traditionally considered a poor experimental model for nephrolithiasis. However, recent studies have identified slc26a6 as an oxalate nephrolithiasis gene in the mouse. Here we extend our earlier demonstration of different anion selectivities of the orthologous mouse and human SLC26A6 polypeptides to investigate the correlation between species-specific differences in SLC26A6 oxalate/anion exchange properties as expressed in Xenopus oocytes and in reported nephrolithiasis susceptibility. We find that human SLC26A6 mediates minimal rates of Cl, exchange for Cl,, sulphate or formate, but rates of oxalate/Cl, exchange roughly equivalent to those of mouse slc2a6. Both transporters exhibit highly cooperative dependence of oxalate efflux rate on extracellular [Cl,], but whereas the K1/2 for extracellular [Cl,] is only 8 mm for mouse slc26a6, that for human SLC26A6 is 62 mm. This latter value approximates the reported mean luminal [Cl,] of postprandial human jejunal chyme, and reflects contributions from both transmembrane and C-terminal cytoplasmic domains of human SLC26A6. Human SLC26A6 variant V185M exhibits altered [Cl,] dependence and reduced rates of oxalate/Cl, exchange. Whereas mouse slc26a6 mediates bidirectional electrogenic oxalate/Cl, exchange, human SLC26A6-mediated oxalate transport appears to be electroneutral. We hypothesize that the low extracellular Cl, affinity and apparent electroneutrality of oxalate efflux characterizing human SLC26A6 may partially explain the high human susceptibility to nephrolithiasis relative to that of mouse. SLC26A6 sequence variant(s) are candidate risk modifiers for nephrolithiasis. [source] Basolateral anion transport mechanisms underlying fluid secretion by mouse, rat and guinea-pig pancreatic ductsTHE JOURNAL OF PHYSIOLOGY, Issue 2 2004M. Paz Fernández-Salazar Fluid secretion by interlobular pancreatic ducts was determined by using video microscopy to measure the rate of swelling of isolated duct segments that had sealed following overnight culture. The aim was to compare the HCO3, requirement for secretin-evoked secretion in mouse, rat and guinea-pig pancreas. In mouse and rat ducts, fluid secretion could be evoked by 10 nm secretin and 5 ,m forskolin in the absence of extracellular HCO3,. In guinea-pig ducts, however, fluid secretion was totally dependent on HCO3,. Forskolin-stimulated fluid secretion by mouse and rat ducts in the absence of HCO3, was dependent on extracellular Cl, and was completely inhibited by bumetanide (30 ,m). It was therefore probably mediated by a basolateral Na+,K+,2Cl, cotransporter. In the presence of HCO3,, forskolin-stimulated fluid secretion was reduced ,40% by bumetanide, ,50% by inhibitors of basolateral HCO3, uptake (3 ,m EIPA and 500 ,m H2DIDS), and was totally abolished by simultaneous application of all three inhibitors. We conclude that the driving force for secretin-evoked fluid secretion by mouse and rat ducts is provided by parallel basolateral mechanisms: Na+,H+ exchange and Na+,HCO3, cotransport mediating HCO3, uptake, and Na+,K+,2Cl, cotransport mediating Cl, uptake. The absence or inactivity of the Cl, uptake pathway in the guinea-pig pancreatic ducts may help to account for the much higher concentrations of HCO3, secreted in this species. [source] | ||||||||||