The intestinal epithelium of vertebrates serves an important barrier function controlling the movement of ions, nutrients, and water into the animal. The major objective of the proposed project is to determine the mechanisms by which specific ion channels in the intestinal epithelium contribute to the transepithelial chemical and electrical potential profiles which serve as the driving forces for absorption of ions and nutrients. These specific ion channels located in the apical (luminal) and basolateral (blood side) cell membranes, together with ion transporters and the resistance properties of the paracellular pathway between intestinal epithelial cells are the bases of the transepithelial potential profiles. Hormonal and pharmacological agents can alter transport processes through effects directly or indirectly on membrane channels and carriers. Using intracellular microelectrode, patch clamp and reconstituted membrane vesicle techniques, we will examine the voltage- and chemical-dependence of these specific ion channels in the teleost, goby, intestine. These biophysical and physiological investigations will increase understanding of the role of the intestine in fluid and electrolyte balance. The intestine of vertebrate animals serves not only to absorb nutrients from food, but also to regulate salt and water balance. This is particularly clear in seawater-adapted fishes in which there is a tendency for body water to be lost and salts gained from the salty environment. The goby is a small fish that has the physiological ability to adapt to a wide range of salt concentrations in its environment, and therefore is a very useful organism in which to study the ion transport mechanisms underlying the regulation of salt and water balance. Much has been learned about the transport of salts across the whole intestine of this interesting fish, but the detailed pathways and mechanisms of regulation of passage of ions across the membranes of this tissue have not yet been worked out. This study will apply the latest methods of patch clamp electrical recording in combination with biochemical analysis of the intracellular effects of hormones that affect ion channels involved in salt transport. The results of this research will contribute significantly to our understanding of the physiological function of intestinal cells.
