Enzyme Secretion Mediated by the Epinephrine β-Receptor in Rat Parotid Slices

Enzyme secretion caused by epinephrine in rat parotid slices is accelerated by addition of inosine and adenine to the medium. The purines apparently aid in maintaining the ATP supply. Epinephrine causes a decrease of the intracellular ATP concentration within 1 min after its addition to the slices. Ouabain which inhibits the Na+,K+-activated ATPase, thus conserving ATP, accelerates enzyme secretion induced by epinephrine. Therefore, it is tentatively concluded that the Na+,K+-activated ATPase is not involved in enzyme secretion. Conditions which produce a high extent of enzyme secretion (g80% of the total amylase secreted in 90 min) are defined and analyzed. In the presence of epinephrine, a high extent of enzyme secretion is obtained when calcium is omitted from the medium or when the potassium in the medium is raised from 5 to 50 mm. When epinephrine is replaced by isoproterenol or by N6-monobutyryl 3',5'-adenosine monophosphate, a high extent of enzyme secretion is obtained also in the regular Krebs-Ringer bicarbonate medium which contains 5 mm potassium and 2.5 mm calcium. The reagents which produce a high extent of enzyme secretion are those which activate the process without concomitantly activating the release of potassium from the slices. It is shown in the accompanying papers that the potassium release is specifically induced by an epinephrine α-receptor.