Differences in the regulatory mechanism of amylase release by rat parotid and submandibular glands

Abstract

It is not known whether the mechanisms involved in amylase release in submandibular and parotid glands are similar. Here, the participation of different signalling pathways in amylase release by the parotid and submandibular glands of the male rat was compared by studying the secretory response after β-adrenergic stimulation. The β-adrenergic agonist isoproterenol induced an increase of cAMP in both salivary glands, but while in the parotid it triggered amylase release, in the submandibular it was unable to increase amylase secretion. Parotid amylase release was dependent on adenylate cyclase activation, as SQ-22536 inhibited the secretory effect. In contrast, submandibular amylase secretion did not depend on the intracellular concentration of cAMP, as SQ-22536 did not modify its secretory response. Moreover, other activators of adenylate cyclase, such as forskolin and prostaglandin E 2, also failed to modify amylase release by the submandibular gland. Neither ionophores nor calcium-blocking agents, as well as calcium–calmodulin and nitric oxide synthase inhibitors, were effective in modifying basal amylase release by the submandibular gland. However, the disruption of microfilaments with cytochalasin B, but not the disruption of microtubules with colchicine, prevented amylase release in that gland. It is concluded that amylase exocytosis in the submandibular gland is a constitutive non-regulated phenomenon, as it is independent of extracellular or intracellular signals. It depends only on the integrity of the microfilaments, probably used by the vesicles to travel from the Golgi apparatus to the plasma membrane.