Escherichia coli heat stable enterotoxin receptors & guanylyl cyclase activity in the intestinal brush border membrane of hamsters & guinea pigs.

BACKGROUND & OBJECTIVES: Although Escherichia coli heat stable enterotoxin (STa) causes diarrhoea in laboratory animals, no studies were done to find out the species specific variation of distribution of the STa receptors in laboratory animals. The present investigation evaluates the density of STa receptors and the guanylyl cyclase (GC) activity in the small intestinal epithelial cells of hamsters and guinea pigs. METHODS: Brush border membrane (BBM) was prepared from the small intestines of hamsters and guinea pigs. Receptor binding assay, GC assay and autoradiography were performed to determine the density of STa receptors, the GC activity and molecular weights of the STa binding proteins respectively. RESULTS: The receptor densities, per mg BBM protein at equilibrium, were found to be 4.1 x 10(9) and 1.5 x 10(12) in hamsters and guinea pigs respectively. The GC activity was found to be lower in STa treated hamster BBM compared to that of guinea pig. Scatchard analysis of the stoichiometric data showed a linear plot, and STa bound with association constants of 0.31 x 10(12) M-1 and 1.04 x 10(12) M-1 in hamsters and guinea pigs respectively. Autoradiographic analysis of the SDS-PAGE, revealed that 125I-STa bound apparently to a 45 kDa membrane protein in hamster and a 115 kDa membrane protein in guinea pig. INTERPRETATION & CONCLUSIONS: It appears that a lower density of STa receptor exists in hamsters compared to that in guinea pigs. STa binds with a single population of STa receptors in each species with different ligand binding affinities. Also, the molecular weights of the STa binding proteins differ in these species. Moreover, the GC activity was found to be lower in hamsters than in guinea pigs.

Rise in free intracellular calcium in HeLa cells infected with aggregative Klebsiella pneumoniae strains isolated from cases of diarrhoea.

BACKGROUND & OBJECTIVES: Klebsiella pneumoniae strains occasionally cause diarrhoea in humans. This study was done to determine the involvement of calcium in the pathogenesis of aggregative K. pneumoniae strains. METHODS: A total of nine strains of K. pneumoniae were tested for adherence assay in HeLa cell line. A representative strain CO-1215 was used for [Ca2+]i study using Fura-2 fluorescence. RESULTS: Infection of cultured HeLa cells with aggregative K. pneumoniae strain resulted in five-fold elevation of intracellular level of free calcium ([Ca2+]i) with maximum Ca2+ influx at 3 h after bacterial infection. Chelation of extracellular Ca2+ with [ethylenebis(oxyethylenenitrile)] tetraacetic acid and suspension of cells in Ca2+ free buffer suggested that the rise of Ca2+ in aggregative K. pneumoniae infected HeLa cells was due to influx of Ca2+ from extracellular medium. INTERPRETATION & CONCLUSIONS: This study showed aggregative adherence in HeLa cells and this adherence leads to influx of extracellular Ca2+. The unrestricted passage of calcium ions across cell membranes could cause phosphorylation of proteins involved in ion transport across the membrane, which could result in secretory diarrhoea. Further work is in progress to study the enterotoxicity of these strains in an in vitro rabbit intestinal model.

Biological activity & interaction of Vibrio cholerae bacteriophages in rabbit ileal loop.

A set of ten V. cholerae EITor phages is in routine use for phage typing of V. cholerae O1 biotype EITor strains. These phages were used in rabbit ileal loop experiment to investigate whether these phages have any prophylactic value as regards their lytic capability on V. cholerae strains. The phages were found to have no prophylactic use as they were unable to lyse the standard bacterial strain V. cholerae MAK 757.

Efeitos da hipoxemia cefalica na circula cao sistemica e pulmonar do cao. / Effects of cephalic hypoxemia in systemic and pulmonary circulation in dogs

Os autores estudaram as repercussoes da estimulacao hipoxia do segmento cefalico sobre a circulacao sanguinea sistemica e pulmonar no cao. Isto foi realizado pela perfusao intermitente das arterias carotidas tanto com sangue arterial quanto venoso usando-se um sistema de perfusao extracorporeo, enquanto, o fluxo sanguineo para o, lobo inferior esquerdo era medido diretamente por fluxometro eletromagnetico colocado em torno de sua arteria e traduzido como fracao do debito cardiaco. A atelectasia do lobo inferior esquerdo foi induzida pelo clampeamento do tubo com balonete colocado no bronquio lobar para isola-lo do pulmao direito remanescente, o qual foi mantido em ventilacao mecanica com oxigenio a 100%. Todos os outros parametros foram determinados por metodos convencionais de laboratorio. Um total de dezessete tratamentos foram executados em oito animais. Os resultados mostraram estimulo hipoxico eficiente dos quimiorreceptores carotidios traduzido por bradicardia,pressao sanguinea elevada e debito cardiaco diminuido assim como tendencia ao aumento da resistencia vascular pulmonar e de fluxo sanguineo para o lobo pulmonar atelectasico durante a perfusao venosa das carotida