Ion transport regulation in intestinal brush border membranes

In this study we tried to gain a better understanding of the molecular mechanism involved in the regulation of Na+ and Cl- transport systems in the apical membrane of the enterocyte. We therefore examined the effects of the second messengers cAMP, cGMP, Ca2+ and DAGon Na+ and Cl- influx in isolated intestinal BBMV under various conditions and studied the characteristics of lipid phosphorylation and breakdown in isolated BB and BBMV. This so-called ""PI-cycle- has been implicated in the generation of second messengers for hormones, neurotransmitters and growth factors but may also play a more direct role in the regulation of epithelial transport systems. Chapter II is concerned with the characterization of the PI-cycle in BB and BBMV and the effects of ca2+ and GTP analogues on PI turnover. Chapter III deals with measurements of Na+ and Cl- permeabilities in BBMV isolated from rat small intestine and their modulation by intravesicular ca2+ levels. A sensitive method for the determination of Cl-/anion exchange in isolated membrane vesicles and a characterization of this exchange in ileal and jejunal BBMV are presented in Chapter IV. In Chapter V the effects of prephosphorylation of BBMV with ATP and cAMP, cGMP, ca2+ or phorbolester in vitro and with cholera toxin in vivo, on vesicular Cl/ anion exchange and Na+;H+ exchange are described. Finally in Chapter VI a general discussion of the foregoing chapters and an outline for future research is presented.