The goal of this project is to obtain a molecular understanding of solute and water transport across the intestinal epithelium, and to elucidate how these processes are controlled by hormones and toxins. Membrane vesicles isolated from the brush border and basolateral surfaces of epithelial cells will be used to study the mechanisms of solute transport. Transport across the plasma membranes of vesicles will be measured using radioactive tracers and optical probes. Tracers will yield information about diffusive and carrier mediated transport, while optical probes will be used to obtain membrane potentials, ion permeability ratios, and net fluxes. These methods will be used to examine in detail ion conductive pathways (channels), KC1 symport, and C1/OH antiport in basolateral membranes, and Na-cotransport systems (Na-lactate) in brush border membranes. In the long term we propose to study these processes by electrophysiological techniques in planar bilayers (""""""""patch-clamp"""""""" preparations). Regulation of ion transport systems in plasma membranes by hormones (e.g., VIP) will also be explored by these techniques, and interactions between hormones, receptors and cyclases will be evaluated by radiation inactivation analysis. This project should provide a clear understanding of ion and solute transport across the epithelial cells of the small intestine in health and disease. In particular, our studies will provide insight into the molecular mechanisms of secretory diarrhea caused by hormones (e.g., VIP) and toxins (e.g., cholera toxin).
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