Isoproterenol and cAMP Block ERK Phosphorylation and Enhance [Ca2+] Increases and Oxygen Consumption by Muscarinic Receptor Stimulation in Rat Parotid and Submandibular Acinar Cells

Abstract

Salivary glands are innervated by sympathetic and parasympathetic neurons, which release neurotransmitters that promote fluid secretion and exocytosis when they bind to muscarinic and ␤-adrenergic receptors, respectively. Signaling pathways downstream of these receptors are mainly distinct, but there is cross-talk that affects receptor-dependent events. Here we report that the ␤-adrenergic ligand isoproterenol blocks increases in extracellular signal-related kinase (ERK) phosphorylation, a protein kinase C-dependent event promoted by the muscarinic receptor ligand carbachol in freshly dispersed rat parotid acinar cells. The inhibitory action of isoproterenol was reproduced by cAMP stimuli ( Almost all mammalian cells have multiple types of heptahelical G-protein-coupled receptors. The muscarinic receptor and ␤-adrenergic receptor are G-protein-coupled receptors that affect the physiological activities of many cells, and neurotransmitters binding to these receptors produce well defined and mainly separate functional effects in salivary glands, which are innervated by both sympathetic and parasympathetic neurons (1). Parotid acinar cells express M3 muscarinic receptors (2), which are coupled via G q to phospholipase C, and acetylcholine and M3R 2 ligands binding to this receptor initiate the production of the second messengers inositol trisphosphate (InsP 3 ) and diacylglycerol, which elevate the intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) and activate PKC. The increase in intracellular Ca 2ϩ initiates the opening of ion channels, electrolyte and fluid secretion, and subsequently, the formation of saliva in the oral cavity (3). In contrast, the activation of parotid ␤-adrenergic receptors promotes exocytosis and the release of amylase protein into the oral cavity. ␤-Adrenergic receptors are coupled via G s to adenylyl cyclase, and receptor stimulation generates the production of cAMP (cyclic adenosine monophosphate) and the activation of cAMP-dependent protein kinase (protein kinase A (PKA)) and a signaling cascade downstream of PKA. Muscarinic receptors also can promote exocytosis, but this is more limited than that due to ␤-adrenergic signaling (4). In many cells cAMP also can activate exchange proteins directly activated by cAMP (Epac), which are guanine nucleotide exchange factors for the GTPase Rap. Epac is a cAMP-dependent PKA-independent protein that can mediate various signaling and functional events in salivary glands and other cells (5-7). This can produce complications in evaluating the mechanisms of cross-talk that exist when there is combined muscarinic and ␤-adrenergic signaling, which is a focus of the present study.Isoproterenol has other effects on parotid acinar cells in addition to promoting exocytosis of secretory granules. It

<b>Role of pituitary adenylyl cyclase-activating polypeptide in intracellular calcium dynamics of neurons and satellite cells in rat superior cervical </b><b>ganglia </b>

“…In addition, VIP, VPAC1, and VPAC2 agonists failed to induce [Ca 2+ ] i responses in neurons. Some studies have shown that the β-adrenergic receptor agonist isoproterenol failed to induce [Ca 2+ ] i responses in rat parotid and lacrimal gland acinar cells (18,40,47). However, isoproterenol as well as forskolin promoted Ca 2+ release from intracellular stores by stimulating muscarinic and α-adrenergic receptors in rodent parotid acinar cells, which involved PKA-dependent phosphorylation of IP 3 R (3,9,44 ] i responses by U73122, thapsigargin, xestospongin C, and 2-APB in neurons indicated that these are primarily IP 3 -dependent.…”

P2X4ou P2X7

“…L'isoprotérénol, un agoniste des récepteurs -adrénergiques, inhibe la phosphorylation de la protéine ERK1/2 en aval de l'activation du récepteur P2X 7 [31]. En revanche, au niveau des glandes sous-maxillaires, des résultats divergents ont été obtenus.…”

Muscarinic Type 3 Receptor Induces Cytoprotective Signaling in Salivary Gland Cells through Epidermal Growth Factor Receptor Transactivation

“…However, mitogenic signaling pathways such as those involving PKC, ERK, and Akt, as well as their M3R-mediated downstream events, are still poorly understood in the context of salivary gland cells. Only recently has a muscarinic receptor agonist, namely, carbachol (CCh), been reported to stimulate in vitro ERK phosphorylation in human immortalized salivary gland cells or rat submandibular acinar cells (Soltoff and Hedden, 2010). Because SjS is a chronic degenerative disease characterized by the gradual progression of cell apoptosis and resulting tissue destruction, it is plausible that mitogenic signaling, which can down-regulate apoptosis induced through the caspase pathway (Steelman et al, 2008), may play a role in sustaining the configuration and functions of affected glands.…”