Heterogeneity of pH in the aqueous cytoplasm of renal proximal tubule cells

Heterogeneity of cytosolic pH was studied with compounds that distribute between the cytosol and mitochondrial matrix in fundamentally different ways, i.e., according to the extent of ionization or according to the function of H+-coupled transport systems. Results show that the average cytosolic pH is considerably more alkaline than the region to which mitochondria are exposed. Because mitochondria are localized predominantly in the basal region, the results are consistent with a transcellular pH gradient within the cytosol of proximal tubule cells. Experiments analyzing the effects of inhibiting efflux of HCO3- at the basal surface and Na+-H+ exchange at the apical surface support the interpretation that the function of these systems contributes to the transcellular pH gradient. The existence of a heterogeneity in pH within the cytosol has important implications concerning the function and regulation of numerous cell processes.     

Inhibition of glutathione efflux from isolated rat hepatocytes by methionine

A substantial inhibition (50-70%) of GSH efflux by methionine was demonstrated in hepatocytes isolated from fed rats. Concurrent measurements of intracellular GSH revealed maintenance of a higher concentration in methionine-supplemented cells over the 1-h incubation. Analysis of total GSH suggested that maintenance of higher intracellular GSH by methionine could be quantitatively accounted for by inhibition of GSH efflux rather than by net GSH synthesis. This conclusion was supported by studies with propargylglycine, a potent inhibitor of cysteine synthesis from methionine. Identical results were obtained in incubations containing either propargylglycine and methionine or methionine alone, thereby suggesting that net synthesis of GSH from methionine was minimal under the assay conditions. Similar decreases (40-60%) in the rate of extracellular accumulation of GSH were observed with ethionine and buthionine, two higher homologs of methionine, but not with a wide range of other naturally occurring and synthetic amino acids. The inhibition of GSH efflux by methionine was not dependent on the presence of sodium in the medium and did not correlate with metabolic consumption of ATP.     

State-dependent valuation learning in fish: banded tetras prefer stimuli associated with greater past deprivation

Humans and some birds and insects sometimes prefer alternatives associated with greater past cost or need, sometimes affording losses. It has been proposed that this is widespread because learning may include knowledge about both the physical properties of alternatives and state-dependent fitness gains. We examine the phenomenon for the first time in a fish, the banded tetra (Astyanax fasciatus). During training we paired two different color cues to identical food rewards, one under greater deprivation than the other. We then tested preference between these cues under both deprivation states. Consistent with previous results in other taxa, the fish preferred the cue associated with previous greater deprivation regardless of the condition under which they were tested. These results provide further support to the view that organisms assign value using state-dependent increments in fitness during learning. Although generally adaptive, under experimental conditions state-dependent valuation learning can lead to paradoxical choices.     

Environmental surveillance and molecular characterization of human enteric viruses in tropical urban wastewaters

Aims: To study the prevalence and genotypes of waterborne pathogenic viruses in urban wastewaters in the tropical region. Methods and Results: Viruses in wastewaters collected at three water reclamation plants in Singapore were studied by molecular methods. Over a 6‐month sampling period, adenoviruses, astroviruses and both norovirus genogroups I (GI) and II (GII) were detected in 100% of the sewage and secondary effluent. Enteroviruses and hepatitis A viruses (HAV) were found in 94 and 78% of sewage, and 89 and 28% of secondary effluent, respectively. By using quantitative real‐time PCR, estimated concentrations of astrovirus in the sewage were 1–2 orders of magnitude higher than those for adenovirus, noroviruses GI and GII. Genotyping of environmental isolates revealed multiple genotypes of GI and GII noroviruses. Coxsackieviruses A, astrovirus type 1 and adenovirus type 41 were prevalent. Norovirus GII/4 and coxsackievirus A24 isolates in wastewaters were closely related to respective outbreak strains isolated previously in Singapore. Conclusions: This study showed the widespread occurrence of all tested enteric virus groups in urban wastewaters. Genetic diversity of astroviruses, enteroviruses and noroviruses in the tropical region was observed. Significance and Impact of the Study: The high prevalence and great genetic diversity of human enteric viruses in urban wastewaters strongly supports the need of further comprehensive studies for evaluating the public health risk associated with viral pathogens in water environments.     

Ultrastructural study of the male gamete of Pleurogonius truncatus Prudhoe, 1944 (Platyhelminthes, Digenea, Pronocephalidae) parasite of Eretmochelys imbricata (Linnaeus, 1766)

In Pronocephaloidea, the spermatozoa of only two species have been studied today. Because of this, we present in this work data concerning to a third specie, Pleurogonius truncatus Prudhoe, 1944. The mature spermatozoon of P. truncatus possesses two axonemes with the 9+"1" pattern typical of Trepaxonemata, mitochondrion, nucleus, parallel cortical microtubules, spinelike bodies, cytoplasmic expansion and an external ornamentation of the plasma membrane. A particularity of the spermatozoon of P. truncatus is in the ultrastructure of the anterior spermatozoon extremity with only cortical microtubules and ornamentation of the plasma membrane. This type of anterior extremity has never been described until today in Pronocephaloidea. On the other hand, the ultrastructure of the posterior extremity of the spermatozoon confirms that already described in Pronocephalidae.