Relationship between cAMP and Ca2+ fluxes in human platelet membranes

The effect of cAMP (which involved a 23 kDa protein phosphorylation) has been studied on the Ca2+ uptake and Ca2+ release from a human platelet membrane vesicle fraction. It was tested in the presence of the catalytic subunit of the cAMP-dependent protein kinase (C Sub). The addition of C Sub increased the steady state level of the Ca2+ uptake into the membrane vesicles. The effect was enhanced when tested in the absence of Ca2+ precipitating agent. The response was proportional to the dose of C Sub. Moreover, the effect varied with the Ca2+ concentration. The effect of C Sub has been tested on the inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release. A phosphorylated state of the 23 kDa protein appeared to be necessary. Indeed, a phosphorylation inhibition prevented the IP3 effect and the addition of C Sub increased the percentage of released Ca2+ (without modification of the time course). However, the C Sub dose-dependent response was not linear. The effect of cAMP on the two functions (Ca2+ uptake and Ca2+ release) appears to be different. Therefore, these results led us to suggest a more complex role of cAMP in the regulation of platelet Ca2+ concentration.     

A catalogue of some ecuadorean fermented beverages,with notes on their microflora

Summary A catalogue of indigenous fermented beverages produced by different ethnic groups in Ecuador has been compiled and the microflora of selected examples examined. A diversity of fermentation substrates was encountered depending on the climatic zone. The fermentations are typicallyLactobacillus spp.—yeast fermentations except for one which includes a mould fermentation by a mixed starter ofMoniha sitophila, Rhizopus stolonifer and aFusarium sp. A discussion is made of the role of these beverages in the human ecology of certain regions.

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Resumen Se ha confeccionado un catálogo de bebidas indígenas ecuatorianas producidas por distintos grupos étnicos, examinándose la microflora de algunos ejemplos seleccionados. Las fermentaciones son generalmente del tipoLactobacillus sp.—levaduras, excepto en un caso que incluye una fermentación fúngica iniciada de forma mixta porM. sitophila, R. stolonifer y unFusarium sp. Se discute el papel de estas bebidas en la ecologia humana de ciertas regiones.

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Résumé Un catalogue des boissons fermentées indigènes produites par divers groupes ethniques de l'Equateur a été compilé et les micro-flores des exemples sélectionnés ont été éxaminés. Les substrats de fermentation varient d'une région climatique à l'autre. Les fermentations sont généralement du typeLactobacillus sp — levures, sauf dans un cas qui comporte une fermentation par des moisissures, avec un mélange initial deMoniha sitophila, Rhizopus stolonifer et une espèce deFusarium. Le rôle de ces boissons dans l'écologie humaine de certaines régions est discuté.

     

Leishmaniasis in Bolivia. IV. The dog in the cycles of leishmaniasis in Bolivia

In Bolivia, the dog is involved in the cycle of visceral leishmaniasis (Leishmania (Le.) chagasi) in the Yungas (alt. 1,000-2,000 m), and also in the cycle of cutaneous leishmaniasis (Le. (V.) braziliensis) in the Alto Beni (alt. 400-600 m). But it plays a different role in the two cycles. In the Yungas focus, it is the main reservoir of Le. (Le.) chagasi and the source of contamination for man. In the Alto Beni focus, it is only a "victim-host", like man, of Le. (V.) braziliensis; the reservoir of which is unknown. Wild mammals are very likely to be involved.     

Seasonal and inter-annual variations of nitrogen diagenesis in the sediments of a recently impounded basin

The Méry-sur-Oise (France) storage reservoir is an artificial basin of 9 m average depth, fed by water from the river Oise with a mean residence time of about 4 days. Sediments are accumulating at a rate of about 0.7 cm/month. In the sediments, two fractions of organic nitrogen with different rates of bacterial degradation could be distinguished, one associated with fresh phytoplankton, the other made of detrital and more refractory compounds. The fluxes of oxygen, nitrate and ammonium across the sediment-water interface were measured with a bell-jar system at different seasons during a 3 year period following flooding of the basin. The measurements show clear seasonal variations in relation with the variations of temperature and input of fresh phytoplanktonic material to the sediment. In addition, a long term trend of increasing ammonium was observed. Measurements were also carried out after dredging of all accumulated sediments of the basin. They showed a considerable reduction of the flux of nitrate to the sediments and a significant reduction of the flux of ammonium to the water column.These results are interpreted in the light of a non stationary model of N diagenesis in accumulating sediments. This model is able to predict at least the general trends of benthic N cycling of basins during the early stage of their ecological succession.     

Sequence divergence and open regions of RNA secondary structures in the envelope regions of the 17 human immunodeficiency virus isolates.

Genetic variation during the course of infection of an individual is a remarkable feature of the acquired immune deficiency syndrome (AIDS) disease. This variation has been studied for the envelope protein encoding regions of seventeen different sequences from various isolates of human immunodeficiency virus (HIV) using multiple sequence comparison and calculation of variability. The open regions with little intramolecular base pairing in these envelope sequences are predicted by a recently developed statistical method. The minimum length L for a run of hypervariable sites, conserved sites, or open regions that gives significance at the 1% (or 0.1%) level is then determined by a scan statistical method. The results show that significant clusters of open regions predicted at the RNA levels correlate with significant clusters of hypervariable sites in the HIV envelope gene. Those significant genomic variations in HIVs seem to be manifested mainly in the extracellular portion of the envelope protein. Twelve potential antigenic determinants are predicted using an antigenic index method. Interestingly, the majority of the significant hypervariable regions in the exterior envelope protein (gp120) were predicted potential epitopes.     

Two types of K+ channels in the apical membrane of rabbit proximal tubule in primary culture

The patch-clamp technique was used to investigate ionic channels in the apical membrane of rabbit proximal tubule cells in primary culture. Cell-attached recordings revealed the presence of a highly selective K+ channel with a conductance of 130 pS. The channel activity was increased with membrane depolarization. Experiments performed on excised patches showed that the channel activity depended on the free Ca2+ concentration on the cytoplasmic face of the membrane and that decreasing the cytoplasmic pH from 7.2 to 6.0 also decreased the channel activity. In symmetrical 140 mM KCl solutions the channel conductance was 200 pS. The channel was blocked by barium, tetraethylammonium and Leiurus quinquestriatus scorpion venom (from which charybdotoxin is extracted) when applied to the extracellular face of the channel. Barium and quinidine also blocked the channel when applied to the cytoplasmic face of the membrane. Another K+ channel with a conductance of 42 pS in symmetrical KCl solutions was also observed in excised patches. The channel was blocked by barium and apamin, but not by tetraethylammonium applied to the extracellular face of the membrane. Using the whole-cell recording configuration we determined a K+ conductance of 4.96 nS per cell that was blocked by 65% when 10 mM tetraethylammonium was applied to the bathing medium.     

Purification and properties of the DNA-binding protein HPB12 from Bacillus subtilis nucleoid

We report the purification to homogeneity of a 12 KDa protein (HPB12) present in the nucleoids of Bacillus subtilis. From the purification data the abundance of the protein was estimated to about 20,000 monomers per cell. The HPB12 protein is heat-stable and acid-soluble and binds preferentially to supercoiled and linearized double-stranded DNAs. The binding of the protein to the supercoiled DNA occurs very rapidly and appears to be cooperative. Moreover, the complexes are extremely stable and do not dissociate after 90 min. These properties are consistent with a role of the HPB12 protein in the structure of the B. subtilis chromosome.     

Permeability of human granulocytes to dimethyl sulfoxide

The permeability of the membrane of human granulocytes to the permeating solute dimethyl sulfoxide (DMSO) was studied using the Onsager form of the phenomenological equations derived from the theory of irreversible thermodynamics. Changes in cellular volume were monitored with an electronic particle counter as samples of that population were introduced into hypertonic osmotica. Temperature and concentration sensitivity analyses of the permeability coefficients were carried out. It is shown that the introduction of the Onsager formalism allows further insight into the observed transport phenomena. It was found that DMSO may affect the water permeability properties of the membrane for that population of cells.