The small intestine of the urodele Amphiuma transports HCO3-minus in the absorptive and secretory directions. The aim of this work is to define the relationship between these two movements of HCO3-minus and the transport of other ions. Double-barreled liquid ion-exchange microelectrodes selective for HCO3-minus will be used to measure the intracellular activity of HCO3-minus and the mucosal membrane potential in cells lining the intestinal villus under normal conditions and after replacement of media C1-minus, or Na ion, exposure to Na ion or Cl-minus transport inhibitors and exposure to agents which elevate intracellular cyclic AMP. In addition the intracellular activity of K ion will also be measured since the absorption of HCO3-minus has been observed to be reduced by ouabain or replacement of media K ion but not Na ion. Cell K ion activity, the mucosal membrane potential, the short-circuit current and voltage divider ratio will be monitored under normal conditions and under conditions known to alter HCO3-minus absorption. Since the transport of HCO3-minus is linked tightly to the transport of Na ion, Cl minus and K ion these observations will furnish a more clear understanding of the normal mechanisms of ion transport in the small intestine.