Induction of amylase release from rat parotid acinar cells by cooling in vitro

As amylase exocytosis from parotid acinar cells is an energy-dependent process, it was supposed that it could be terminated by cooling on ice. Unexpectedly, however, the cooling itself markedly induced amylase release from parotid acini. The release finished within 1 min and prolonged incubation on ice did not cause further release. The cold-induced amylase release was observed in the absence of extracellular calcium, and calcium ionophore A23187 neither enhanced nor inhibited it. Treatments with cytochalasin D, phalloidin, or taxol did not disturb the release. Cold treatment did not increase the leakage of lactate dehydrogenase, a cytosolic enzyme, and the acini still maintained normal responsiveness to isoproterenol. Electron-microscopic observation revealed that the plasma membrane and zymogen granules of cold-exposed acini were intact, but many acinar lumina were distended with secretory materials. These results suggest that the cold treatment induces transient amylase release by the fusion of plasma membrane and the zymogen granules that have been closely docked at the luminal membrane.