The Role of Calmodulin in Rat Parotid Amylase Secretion: Effects of Calmodulin Antagonists on Secretion and Acinar Cell Structure

Abstract

Using dispersed rat parotid cells, the effects of three calmodulin antagonists, trifluoperazine (TFP), N-(6-aminohexyl)-5-chloro-1 -naphthalenesul-fonamide (W-7), and N-(6-aminohexyl)-1 -naphthalenesulfonamide (W-5), on amylase release and acinar cell structure were examined. TFP and W-7 strongly inhibited both isoproterenol (ISO)- and dibutyryl cyclic AMP-stimulated amylase release at a concentration of 50 or 100 μM, while W-5, a weak calmodulin antagonist, had only little effect. Cyclic AMP level was markedly elevated by ISO even in the presence of TFP or W-7. These results indicate that the calmodulin antagonists affect amylase release at steps distal to cyclic AMP metabolism. Electron micrographs demonstrated that treatment of parotid cells with either TFP or W-7 caused a loss of luminal microvilli and surface folds. When cells were stimulated by ISO in the presence of TFP or W-7, the enlarged lumina did not recover to their original size and the discharged secretory material was retained in the lumina. Numerous secretory granules remained in the acinar cytoplasm. W-5 affected the acinar cell structure only a little. These observations lead to the assumption that TFP and W-7 interfered with the normal functions of the cytoskeletal system. It is proposed that calmodulin may be involved in the exocytosis of parotid amylase through the regulation of the cytoskeletal system.