Influence of external potassium concentration on secretory responses to cholecystokinin-pancreozymin and ionophore A23187 in the pancreatic acinar cell.

1. The inhibitory effect of a diminution in [K+]o on the secretory processes of the pancreatic acinar cell was analysed in the isolated and perfused rat pancreas. 2. Partial replacement of KCl with NaCl produced falls in both amylase output and pancreatic juice flow which were induced by 5 m-u. cholecystokinin-pancreozymin (CCK-PZ)/ml., and the responses were slowly regained after reintroduction of a standard concentration of KCl. 3. A quantitative relation was found between the amount of amylase released by CCK-PZ and [K+]o over the range 1.0--5.6 mM. A linear relation was obtained between the ratio of E1K+]3(0)/amylase output and [K+]3(0). 4. A quantitative relation was also found between the pancreatic juice flow induced by CCK-PZ and [K+]o over the range 1.0--5.6 mM. A linear relation was obtained between the ratio of [K+]3(0)/juice flow and [K+]3(0). 5. The results obtained may be explained by a model as follows: (1) amylase output and juice flow induced by CCK-PZ are simply proportional to the amount of complex composed of a carrier molecule bearing one Ca and four Na atoms, (2) the inward movement of the complex is tightly linked to the CCK-PZ-induced activation of pumps which are postulated on both basal and apical sides of the membrane of the acinar cell, and (3) the Na:K coupling ratio of the pumps is close to 3:2. 6. A quantitative relation was also found between the amount of amylase released by Ca reintroduction after pre-treatment with Ca-ionophore A23187 and [K+]o. This may be explained by a model essentially similar to that mentioned above. 7. Total replacement of NaCl with NaBr slightly reduced the CCK-PZ-induced fluid and amylase secretion. Total replacement of NaCl with sodium isethionate or with sodium pyruvate, however, virtually abolished the CCK-PZ-induced fluid and amylase secretion.