High‐resolution autoradiography of3H‐ouabain binding in salt transporting epithelia

The distribution of salt transporting sites in epithelia is a problem of special interest to electrolyte metabolism. Autoradiography of freeze-dried plastic embedded tissue was used to localize 3H-ouabain in rabbit small intestine and renal medulla and gills of killifish. Resolution approaching theoretical limits for tritium at the light microscope level was achieved. The results of several tests are presented which demonstrate the resolution of the method and the specificity of the observed ouabain binding patterns. A large uptake of ouabain was found along the basolateral membranes of the enterocyte, thick ascending tubules and chloride cells (fish gill).