This proposal will continue studies of intestinal transport with special emphasis on calcium. In contrast to the more usual studies, we will attempt to delineate transport mechanisms utilizing the changes occurring in remaining gut following either extensive proximal or distal small bowel resections in the rat. In contrast to prior years, the studies envisaged for the current year will employ mainly in vitro methodology. The principal method will be the short circuit current technique of Ussing and Zerahn, modified for intestinal tissues, whereby a planar sheet of intestinal tissue is clamped between 2 lucite half cells and incubated, usually with identical medium on each side of the tissue. Radionuclide tracer(s) is added to one side and electrical gradients neutralized by an external current source. This will allow quantitation of transport, the ready separation of active from non-active transport, the measurement of unidirectional fluxes across tissues and studies of the effects of electrical as well as chemical gradients. BIBLIOGRAPHIC REFERENCES: Urban, E. and Pena, M. The Effect of Lactose on in vivo Calcium Transport in the Rat. Clin. Research 23:462A (April) 1975 and Am. J. Clin. Nutr. 28:431 (April) 1975. Urban, E. The Effect of Major Small Bowel Resection in Serum Proteins in the Rat. Clin. Research 24: (Jan.) 1976 (In Press).