Water Flow Through Frog Gastric Mucosa

The transport of water through biological membranes can be attributed to several causes. Gradients of chemical activity caused by the application of hydrostatic pressure or differences in solute concentration across the membrane may produce a net water flow, called passive transport (1). In the absence of such gradients a net flow may also occur which is defined as active transport, and is presumed to arise from metabolic processes occurring in the membrane. Pappenhehner, Renkin, and Borrero (2) and Koefoed-Johnsen and Ussing (3) have independently shown that passive flows can be interpreted to give a model of the membrane in terms of pore structure. In the present study two types of experiments have been performed on passive water transport across the isolated gastric mucosa of the frog. First, the unidirectional diffusion flow of water in either direction has been measured using tritiated water as a tracer. Second, an osmotic gradient has been applied across the membrane and a passive net flow has been measured. At the same time an active net flow in the same direction as HC1 secretion has also been observed. In addition to the water transport studies, separate measurements have been made of the restriction offered by the membrane to diffusion of various sized molecules. The combined results of these experiments are interpreted in terms of a polydisperse population of pores in the membrane.