Mechanism of isoproterenol-induced heterologous desensitization of mucin secretion from rat submandibular glands regulation of phosphorylation of Gi proteins controls the cell response to the subsequent stimulation

Abstract

Short-term treatment of rat submandibular tissues with 10 microM isoproterenol (IPR) resulted in reduction of mucin secretion in response to the agonist during further incubation, and in increases in EC50 values. This IPR-induced reduction of secretion was coupled with selective decreases in the number of beta-adrenoceptors in the tissues and in their affinity for agonists, as assessed by measurement of the specific binding of [3H]dihydroalprenolol. Treatment of the tissues with IPR caused a 30% decrease in IPR-stimulated adenylate cyclase activity and a 25% increase in the GTP binding capacity of inhibitory G proteins (Gi proteins). This IPR treatment triggered a 60% increase in the ability of pertussis toxin (IAP) to catalyze ADP-ribosylation of Gi proteins in the tissue membranes. Enhanced function of stimulatory G proteins (Gs proteins) was observed only during the first incubation of the tissues with IPR. The IAP-catalyzed ADP-ribosylation of Gi proteins in tissues treated with IPR was decreased by prior treatment with cyclic AMP dependent protein kinase, but was increased markedly by prior treatment with alkaline phosphatase. Neither IPR-induced desensitization of protein secretion nor increase in the IAP-catalyzed ADP-ribosylation of Gi proteins was observed in the tissues pretreated with 0.25 microM okadaic acid. These findings suggest that the regulation of Gi protein phosphorylation plays an important role in the IPR-induced heterologous desensitization of mucin secretion from rat submandibular glands.

Water Channels and Zymogen Granules in Salivary Glands

“…PKA type I is the membrane-bound form that is activated during β-ADR stimulation and is accompanied by an increase in specific membrane phosphorylation during amylase secretion induced by β-ADR agonists (64,141). These findings suggest that Gi2α protein is selectively phosphorylated by PKA type I, resulting in decreased function and supersensitivity of amylase secretion (6,64,65). 2.…”

“…In parotid tissues supersensitized with IPR, there is a 60% decrease in IAPcatalyzed ADP-ribosylation of Giα (64). Conversely, however, a 40% increase in IAP-catalyzed ADPribosylation of Giα is coupled with the desensitization of amylase and mucin secretion from rat parotid and submandibular tissues induced by IPR and histamine, respectively (6,64,65). In agonist-induced desensitization of AC stimulation in MDCK cells (159) and rat heart muscle cells (160), there are also increases in the level and function of Gi proteins, as measured by IAPcatalyzed ADP-ribosylation and GTP-binding capacities of these proteins.…”

“…Activation of Gs proteins leads to the activation of PKA via the stimulation of AC, suggesting the importance of PKA in the regulation of G protein function. In rat salivary gland, however, changes in the levels and function of Gs proteins, measured as cholera toxin-catalyzed ADP-ribosylation and GTP-binding capacities of these proteins, are not involved in the mechanism underlying IPR-induced supersensitivity, or in IPR-and histamine-induced desensitization of protein secretion from rat parotid (2, 6, 64) and submandibular glands (65). IAP-sensitive G proteins, termed Gi1, Gi2, and Gi3, comprise a family of Gi proteins and Gi2 inhibits adenylate cyclase activity (156).…”

“…Short-term treatment (<10 min) of rat parotid tissues with IPR results in supersensitivity of amylase secretion during further treatment with the same agonist, but longer (>20 min) IPR treatment results in desensitization (2, 64). In submandibular gland tissues, however, IPR treatment for various periods of time only desensitizes mucin secretion from the tissues, but does not induce supersensitivity (65). On the other hand, histamine acts at H 2 receptors and induces amylase secretion from rat parotid gland tissues (6).…”

Activation of Endogenous Nitric Oxide Synthase Coupled with Methacholine-Induced Exocytosis in Rat Parotid Acinar Cells

“…We reported previously that short-term treatment of rat parotid tissue slices with IPR for less than 10 min resulted in supersensitivity of amylase secretion from the tissue slices, but such treatment for more than 20 min resulted in desensitization (Hata et al, 1983), and that such short-term treatments of rat submandibular tissue slices with IPR (Ishikawa et al, 1995) and of rat parotid tissue slices with histamine induced only desensitization of mucin and amylase secretion from the tissue slices, respectively. These phenomena were accompanied by alterations in the number of ␤-adrenoceptors or histamine H 2 receptors in the tissue slices and in the affinity of these receptors for their agonists but no changes in adenylate cyclase activity.…”