The electrogenic sodium pump in the hyperpolarizing and secretory effects of pancreozymin in the pancreatic acinar cell.

1. Transmembrane potential, effective membrane resistance, and amylase release were recorded simultaneously from acinar cells of isolated rat pancreas perfused with Krebs-Henseleit solution. 2. The hyperpolarizing effect of pancreozymin (Pz) was confirmed by perfusing with a solution containing 5 m-u. Pz/ml. 3. The hyperpolarizing effect of Pz disappeared in the following environments: (a) in low ambient temperature, (b) in K-free medium, (c) in low Na medium, and (d) in the presence of ouabain. In these environments, transient depolarization was frequently observed immediately after stimulation. It is suggested that there are two components in the effect of Pz on the membrane potential of the acinar cells: transient depolarization which coincides with an increase in Na permeability in the initial phase, and continuous hyperpolarization due to an electrogenic Na pump which conceals transient depolarizing phase when the pump is dominant. 4. The secretory effect of Pz was inhibited under conditions that suppressed the electrogenic Na pump. It is proposed that the Na pump activated by Pz maintains the passive Na-influx, increases [Ca2+]i, and, in consequence, uphold the amylase output during continuous stimulation. 5. A medium which was used to bathe the sectioned pancreas with Pz was found to contain a substance which depolarized the acinar cells.