We propose to study the relationship between oxidative metabolism and active ionic transport in two transporting systems: acid secretion in the gastric mucosa of the bullfrog (Rana catesbiana) and potassium transport in the midgut of the silkworm (Hyalophora cecropia). These tissues were chosen because no cation-ATPase has been isolated from them, yet the presence of large concentrations of mitochondria near the sites of active transport begs the question of the relationship between oxidative metabolism and epithelial transport. The special approach to be used is the simultaneous measurement of optical properties such as the oxidation-reduction state of the cytochromes, flavoproteins, and NAD in the intact tissue while transport parameters such as short circuit current and open circuit voltage are being monitored. In some experiments, O2 consumption and high energy phosphate concentration will also be measured. Both steady state and kinetic data will be obtained in the presence of various ionic and gaseous environments as well as pharmacological agents affecting the cytochrome chain and/or transport. A possible link between these two systems will be sought on the basis of these responses. Preliminary data indicate that many differences exist between the responses of the respiratory chain of these tissues and those of isolated mitochondria and mitochondria intact skeletal muscle during various conditions of oxidative phosphorylation. These differences in response will be analyzed in terms of possible mitochondrial specializations for direct energy conversion to transport processes. The results of this study are expected to help in a better understanding of the kinetics and energetics of the transport process and the metabolic reactions that subserve it.