Taurocholate transport by brush border membrane vesicles from different regions of chicken intestine.

Taurocholate transport was studied in brush border membrane vesicles (BBMV) isolated from chicken small (duodenum, jejunum, and ileum) and large (proximal cecum and rectum) intestines, using a rapid filtration technique. The purity of the BBMV was verified by the finding that the specific activity of sucrase (a brush border membrane enzyme marker) was severalfold greater in vesicles than corresponding values in mucosal homogenate. The functional integrity of isolated BBMV was evaluated by the uptake of D-glucose, which showed a transient increase in the presence of Na+. A Na+-dependence of taurocholate uptake was shown in BBMV prepared from ileum, cecum, and rectum, as taurocholate transport was transiently increased (accumulation) in the presence of a Na+ gradient between the external medium and intravesicular medium. The magnitude of the accumulation was similar among ileum, cecum, and rectum. In contrast, BBMV prepared from duodenum and jejunum did not show any Na+-dependent taurocholate transport, as the taurocholate uptake was not affected when a Na+ gradient was replaced by a K+ gradient. The use of taurochenodeoxycholate in the incubation medium inhibited Na+-dependent taurocholate transport in the ileum, cecum, and rectum. This study is the first to show the presence of a Na+-dependent bile salt transport in BBMV obtained from chicken ileum, proximal cecum, and rectum.

Increased Na(+)-H+ exchanger activity in the ileal brush-border membrane of spontaneously hypertensive rats.

In the present study, we have examined the intestinal Na+ transport, through the Na+)-H+ exchanger in ileal brush-border membrane vesicles (BBMV) isolated from spontaneously hypertensive rats (SHR), and normotensive Wistar Kyoto (WKY) rats as a control group. Na+ uptake into ileal BBMV was stimulated the presence of a proton gradient (pH 5.5 inside/pH 7.5 outside) in SHR and WKY rats, resulting in a transient accumulation (overshoot) in both groups of rats. No overshoot was observed in the absence of a pH gradient. The magnitude of the accumulation was significantly higher in SHR than in WKY rats. Uptake of Na+ at equilibrium was identical in the presence and the absence of a proton gradient and was not changed in SHR. The use of amiloride inhibited pH gradient-driven Na+ uptake in a dose-dependent manner with a Ki of 90 microM and 100 microM for SHR and WKY rats, respectively. The relationship between proton gradient-driven Na+ uptake and external Na+ concentration was saturable and conformed to Michaelis-Menten kinetics in both SHR and WKY rats. Lineweaver-Burk analysis of the pH gradient-driven Na+ uptake indicated values of Vmax that were significantly increased in SHR compared to WKY rats (11.4 +/- 0.55 nmol/mg/8 s vs. 4.96 +/- 0.78 nmol/mg/8 s for SHR and WKY rats, respectively). In contrast, similar K(m) for Na+ were found between SHR and WKY rats (4.0 +/- 0.2 mM vs. 4.9 +/- 0.6 mM for SHR and WKY rats, respectively). These studies show derangement in ileal BBMV Na+ transport of SHR, which is characterized by increased Na(+)-H+ exchanger activity.

Increased sodium-dependent D-glucose transport in the jejunal brush-border membrane of spontaneously hypertensive rat.

The current studies explore the effect of hypertension on D-glucose transport into jejunal brush-border membrane vesicles (BBMV). Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, as a control group, were used. The purity of the BBMV from both groups of animals was validated by the finding that the specific activity of brush-border enzyme marker, sucrase, was severalfold greater in membrane vesicles compared with corresponding values in mucosal homogenate. D-glucose uptake was Na+ dependent in both groups of animals, with a transient increase in the intravesicular concentration of D-glucose. However, the initial rate and the magnitude of the accumulation of Na+-dependent D-glucose was significantly higher in SHR compared with WKY rats. In order to investigate the mechanism(s) for the increase in Na+-dependent D-glucose transport in SHR, several experiments were performed: (1) an experiment that indicated 22Na uptake, as an indicator for Na+ permeability, was similar between SHR and WKY rats, (2) kinetic studies that indicated that Vmax values of SHR were significantly greater that those of WKY rats. In contrast, similar Km values for glucose were found between SHR and WKY rats, (3) Na+-dependent phlorizin binding measurements that were not altered by hypertension and (4) a study of the brush-border membrane lipid composition that showed a significant increase in the free cholesterol/phospholipid ratio in SHR. We conclude that altered membrane cholesterol content and consequently altered lipid fluidity could be, at least in part, responsible for the observed increase in Na+-dependent D-glucose transport in SHR.