Folate transport by prawn hepatopancreas brush-border membrane vesicles.

The transport system of folic acid (Pte-Glu) b y brush-borde r membrane vesicles (BBMV ) isolated from prawn (Penaeus japonicm) hepatopancreas , was studied by measuring the uptake of Pte-Glu . This uptake was found to have two components , intravesicular transport and membrane binding . Membrane binding was not affected by the presence of a trans - membrane pH-gradient at a short incubation period . However , a transmembrane pH - gradient increased membrane binding at 6 0 min. The transpor to f Pte-Glu appeared to be carrier-mediated , was stimulated by an inwardly proton gradient (p H 5. 5 outside , 7. 4 inside ) and was unaffected by a sodium-gradient . The relationship between pH gradient-driven Pte-Glu uptake and medium Pte-Glu concentration followed saturating Michaelis-Menten kinetics . Eadie-Hofste e representation of the pH gradient-driven Pte-Glu uptake indicated a single transport system with a Km of 0.3 7 ^ Man d Vmax of 1.06pmol/mg protein/15s . These findings indicate that BBM V isolated from prawn hepatopancreas possesses a Pte - Glu transport system similar to that described in mammalian intestine

Distribución y movimiento del colesterol en la membrana de eritrocito de pacientes con hipertensión esencial

The participants were 12 healthy subjects, 12 normocholesterolaemic hypertensive and 12 hypercholesterolaemic hypertensive patients. Venous blood samples were collected in Trabajo ganador del VIII Premio Sociedad Andaluza de Medicina Interna. «Dr. López Laguna» 0.38% sodium citrate. Erythrocyte membrane cholesterol distribution and transbilayer movement were measured according to the continuous cholesterol oxidase treatment. Erythrocyte Na<sup>+</sup>-Li<sup>+</sup> countertransport activity was determined by measurements of Li<sup>+</sup> efflux in the presence or absence of Na<sup>+</sup>.The statistical analysis was conducted for significance by using ANOVA for paired data and correlations were carried out by linear regression analysis using Pearson's correlation coefficient. Our findings are consistent with the presence of cholesterol-rich domains randomly distributed in the human erythrocyte. Cholesterol appeared to be similarly enriched in the cytofacial monolayer but the size of such structural cholesterol pool was greater in erythrocytes of hypertensive patients than in those of healthy subjects. There was also a decrease in the movement rate of erythrocyte membrane cholesterol, which contributed to keep impaired the asymmetric distribution of cholesterol in hypertensive patients. In addition, there was a strong correlation between the half-time for membrane cholesterol distribution or transbilayer movement and erythrocyte Na<sup>+</sup>-Li<sup>+</sup> countertransport activity, a well known marker of inherited predisposition to essential hypertension. Our data indicate that the steady-state distribution of membrane cholesterol and cell cholesterol exchange may be intimately linked to the etiology of essential hypertension, and to other diseases which are associated to alterations in the lipid metabolism.<br><br>El presente estudio se llevó a cabo con 36 personas que se ofrecieron voluntarias, de las cuales 12 eran sujetos sanos, 12 pacientes hipertensos normocolesterolémicos y 12 pacientes hipertensos hipercolesterolémicos. Mediante punción en la vena antecubital, se recogieron muestras de sangre en citrato sódico al 0,38%. La distribución del colesterol y su velocidad de transporte en la membrana de eritrocito se midieron según la técnica de la coiesterol oxidasa. La medida de la velocidad máxima del contratransporte Na<sup>+</sup>-Li <sup>+</sup> en eritrocito se efectuó según el eflujo de Li<sup>+</sup> en presencia o ausencia de Na<sup>+</sup>. El estudio estadístico se determinó según el análisis de varianza (ANOVA) para datos pareados con distribución normal. Para las correlaciones se empleó el test de regresión lineal de Pearson. Los resultados indican que existe una distribución asimétrica del colesterol en la membrana de eritrocito humano (más colesterol en la monocapa interna que en la externa), aunque la monocapa interna del eritrocito de pacientes hipertensos es aún más rica en colesterol que la de sujetos sanos. Esta alteración es concomitante con una reducción de la velocidad de transporte del colesterol en la bicapa lipídica del eritrocito, que contribuye a la asimetría transmembrana y lateral del propio coiesterol. Estos parámetros se correlacionan con la actividad en el eritrocito del contratransporte Na<sup>+</sup>-Li<sup>+</sup>, considerado como un indicador genético de la hipertensión esencial. Puede afirmarse que la distribución del colesterol y su velocidad de transporte entre monocapas pueden desempeñar un papel específico en el proceso hipertensivo. Y, por extensión, en otras enfermedades asociadas con alteraciones en el metabolismo lipídico