Flushing history as a hydrogeological control on the regional distribution of arsenic in shallow groundwater of the Bengal Basin

Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood. We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh. The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of approximately 250 microg/L dissolved As per 1 mg/kg P-mobilizable As. We use this relationship in a simple model of groundwater recharge to propose that the distribution of groundwater As in shallow aquifers of the Bengal Basin could primarily reflect the different flushing histories of sand formations deposited in the region over the past several thousand years.     

D-Glucose enhancement of water reabsorption in proximal tubule of the rat kidney

Water reabsorption in the proximal convoluted tubule of the rat kidney was examined by in vivo microperfusion techniques in order to examine the effect of D-glucose within the tubular lumen. When tubules were perfused with a balanced artificial solution containing Na, K, Cl, HCO3, urea, and D-glucose, absolute reabsorption averaged 4.01 +/- 0.24 nl/min per mm. Addition of D-glucose to the NaCl perfusate enhanced water reabsorption to values similar to those obtained with the balanced artificial perfusate. The enhanced water reabsorption consequent to the addition of D-glucose to the NaCl perfusion solution was completely inhibited by addition of phloridzin to the perfusate. The addition of an unabsorbed hexose, 2-deoxy-D-glucose, to the NaCl perfusate failed to enhance water reabsorption, whereas the addition of an incompletely reabsorbed sugar that is not metabolized, 3-O-methyl-D-glucose, resulted in partial enhancement of theabsolute rate of water reabsorption. These studies demonstrate that D-glucose has the specific effect of augmenting water reabsorption in the proximal tubule of the rat kidney.     

Psychiatric correlates of MR deep white matter lesions in probable Alzheimer's disease

The authors examined the relationship between psychiatric symptoms and the presence of of MR deep white matter lesions (DWMLs) in 28 probable Alzheimer's disease (AD) patients with mild to moderate dementia. The difference in frequency of psychiatric symptoms between patients with and without DWMLs was not statistically significant. However, MR global scores of severity correlated with the presence of ideational disturbances (such as low self-esteem and suicidal ideation). Analysis of specific cerebral regions indicated that the highest correlation occurred in the frontal white matter. Thus, DWMLs are correlated with specific symptoms of depression in AD. Whether DWMLs are etiologically related to these symptoms remains to be determined.     

World-wide lightning location using VLF propagation in the Earth-ionosphere waveguide

Worldwide lightning location (WWLL) using only 30 lightning sensors has been successfully achieved by using only VLF propagation in the Earth-ionosphere waveguide (EIWG). Ground propagation or mixed sky and ground propagation is avoided by requiring evidence of Earth-ionosphere waveguide dispersion. A further requirement is that the lightning strike must be inside the perimeter defined by the lightning sensor sites detecting the stroke. Under these conditions, the time and the location of the stroke can be determined, along with the rms errors. Lightning strokes with errors exceeding 30 Ps or To assist with identifying impulses from the same lightning stroke, the lightning sensor threshold is automatically adjusted to allow an average detection rate of three per second. This largely limits detection to the strongest 4% of all lightning strokes, of which about 40% meet the accuracy requirements for time and location.     

Auger study of Cr/Au thin films deposited on alumina and sapphire

R.f. sputtered Cr/Au films on alumina and sapphire substrates were subjected to thermal annealing treatments at 300 and 450 °C in vacuum and in air. These specimens were studied using Auger depth profiling and by measuring their sheet resistances. These results were analyzed and the Cr-Au interactions are described. At 300°C a grain boundary diffusion coefficient of 4X10^?15 cm²s^?1 for chromium in gold is derived.     

The role of NHERF and E3KARP in the cAMP-mediated inhibition of NHE3

NHE3 is the apically located Na+/H+ exchanger in the gut and in the renal proximal tubule. Acute inhibition of this transporter by cAMP requires the presence of either of two NHE3-associated proteins, NHERF or E3KARP. It has been suggested that these proteins either directly regulate NHE3 activity after being phosphorylated by protein kinase A (PKA) or that they may serve as adapters that localize PKA near NHE3. We studied the role of NHERF and E3KARP in opossum kidney cells, which endogenously express NHE3, NHERF, and ezrin and display cAMP-dependent inhibition of NHE3. In vivo phosphorylation studies showed that NHERF is a phosphoprotein under basal conditions, but does not change its phosphorylation state after 8-bromo-cAMP treatment, and that E3KARP is not phosphorylated at all. Co-immunoprecipitation showed that NHERF and E3KARP bind both NHE3 and ezrin. Using cAMP analogs it was demonstrated that NHE3 activity, measured as sodium-dependent recovery of the intracellular pH after intracellular acidification, is inhibited by PKA type II. Because others have shown that ezrin binds PKA type II and that NHE3 is phosphorylated by PKA we suggest that NHERF and E3KARP are adapters that link NHE3 to ezrin, thereby localizing PKA near NHE3 to allow NHE3 phosphorylation.     

Bile acid uptake via the human apical sodium-bile acid cotransporter is electrogenic

Intestinal absorption of bile acids depends on a sodium-bile acid cotransport protein in the apical membrane of the ileal epithelial cell. Transport is Na+-dependent, but the Na+-bile acid stoichiometry and electrogenicity of transport are not known. Studies in whole intestine, isolated cells, and ileal membrane vesicles have been unable to resolve this issue because transport currents are small and can be obscured by other ionic conductances and transport proteins present in these membranes. In this study, the human apical sodium-bile acid transporter was expressed in stably transfected Chinese hamster ovary cells that lack other bile acid transporters. The Na+-dependent transport of a fluorescent bile acid analog, chenodeoxycholyl-Nepsilon-nitrobenzoxadiazol-lysine, was monitored by fluorescence microscopy in single, voltage-clamped cells. Bile acid movement was bidirectional and voltage-dependent with negative intracellular voltage-stimulating influx. A 3-fold reduction in extracellular Na+ produced a negative 52 mV shift of the flux-voltage relationship, consistent with a 2:1 Na+:bile acid coupling stoichiometry. No Na+- or voltage-dependent uptake was observed in nontransfected Chinese hamster ovary cells. These results indicate that the cotransport of bile acids and Na+ by human apical sodium-bile acid transporter is electrogenic and bidirectional and is best explained by a 2:1 Na+:bile acid coupling stoichiometry. These results suggest that membrane potential may regulate bile acid transport rates under physiological and pathophysiological conditions.     

Photosensitization of experimental hepatocellular carcinoma with protoporphyrin synthesized from administered delta-aminolevulinic acid: studies with cultured cells and implanted tumors

The use of ultrasonography, traditionally performed by radiologists, is becoming increasingly widespread in emergency medicine. Consequently, much debate has evolved over whether emergency medicine physicians are qualified to provide this service, and the criteria by which training and credentialing can be achieved. This article discusses training and credentialing guidelines, paths to becoming credentialed in emergency sonography, and quality assurance issues. Also, strategies are proposed for emergency departments seeking to perform emergency sonography.