Adrenergic and cholinergic regulation of phospholipid release in sublingual salivary gland in vitro

Salivary phospholipid secretion in response to beta-adrenergic stimulation is mediated by Src kinase-dependent epidermal growth factor receptor transactivation

Communication between receptor tyrosine kinase and G protein-coupled receptor (GPCR)-mediated signaling is recognized as a common integrator linking diverse aspects of intracellular signaling systems. Here, we report that G protein-coupled beta-adrenergic receptor activation leading to stimulation of salivary phospholipid release occurs with the involvement of epidermal growth factor receptor (EGFR). Using sublingual gland acinar cells, we show that prosecretory effect of isoproterenol on phospholipid release was subjected to suppression by EGFR kinase inhibitor, PD153035, and wortmannin, an inhibitor of PI3K, but not by PD98059, an inhibitor of extracellular signal regulated kinase (ERK). Furthermore, wortmannin, but not the ERK inhibitor, caused the reduction in the acinar cell secretory responses to beta-adrenergic agonist-generated cAMP as well as adenyl cyclase activator, forskolin. The acinar cell phospholipid secretory responses to isoproterenol, moreover, were inhibited by PP2, a selective inhibitor of tyrosine kinase Src responsible for ligand-independent EGFR phosphorylation. Taken together, our data are the first to demonstrate the requirement for Src kinase-dependent EGFR transactivation in regulation of salivary phospholipid secretion in response to beta-adrenergic GPCR activation.

Role of nitric oxide and beta-adrenoceptors of the central nervous system on the salivary flow induced by pilocarpine injection into the lateral ventricle

Our studies have focused on the effect of L-NG-nitroarginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), and L-arginine, the substrate of NOS, on salivary secretion induced by the administration of pilocarpine into the lateral cerebral ventricle (LV) of rats. The present study has also investigated the role of the beta-adrenergic agonists and antagonist injected into LV on the salivary secretion elicited by the injection of pilocarpine into LV. Male Holtzman rats with a stainless-steel cannula implanted into the LV were used. The amount of salivary secretion was studied over a 7-min period after injection of pilocarpine, isoproterenol, propranolol, salbutamol, salmeterol, L-NAME and L-arginine. The injection of pilocarpine (10, 20, 40, 80 and 160 microg/microl) into LV produced a dose-dependent increase in salivary secretion. The injection of L-NAME (40 microg/microl) into LV alone produced an increase in salivary secretion. The injection of L-NAME into LV previous to the injection of pilocarpine produced an increase in salivary secretion. L-Arginine (30 microg/microl) injected alone into LV produced no change in salivary secretion. L-Arginine injected into LV attenuated pilocarpine-induced salivary secretion. The isoproterenol (40 nmol/microl) injected into LV increased the salivary secretion. When injected previous to pilocarpine at a dose of 20 and 40 microg/microl, isoproterenol produced an additive effect on pilocarpine-induced salivary secretion. The 40-nmol/microl dose of propranolol injected alone or previous to pilocarpine into LV attenuated the pilocarpine-induced salivary secretion. The injection of salbutamol (40 nmol/microl), a specific beta-2 agonist, injected alone into LV produced no change in salivary secretion and when injected previous to pilocarpine produced an increase in salivary secretion. The 40-nmol/microl dose of salmeterol, a long-acting beta-2 agonist, injected into LV alone or previous to pilocarpine produced no change in salivary secretion. The results have shown that central injections of L-NAME and L-arginine interfere with the salivary secretion, which implies that might participate in pilocarpine-induced salivary secretion. The interaction between cholinergic and beta-adrenergic receptors of the central nervous system (CNS) for the control of salivary secretion can also be postulated.

Characterization and partial purification of a keratinocyte-derived growth factor with wound-healing properties

We have previously described the mitogenic and wound-healing properties of keratinocyte-conditioned medium (KCM). In this study we investigated the effect of KCM on the activation of second messenger systems and the expression of proto-oncogene in cultured human skin fibroblasts. We also present a partial purification of the factor responsible for the mitogenic and wound-healing effects of KCM. KCM was shown to increase the expression of the proto-oncogenes c-fos, c-myc and c-jun. The effect of KCM on three second messenger systems was investigated. The extracellular release of choline metabolites was increased by 40 per cent when cells were stimulated with KCM whereas the formation of cAMP and hydrolysis of phosphatidyl inositol (PI) was unaffected. KCM was purified by ion exchange chromatography and filtration. The biologically active fraction was eluted from an SP column and retained its activity after filtration through a 3-kDa filter. The fraction was inactivated by heat and acid, indicative of a peptide origin. Furthermore, the active fraction was shown to increase the extracellular release of choline metabolites and to stimulate re-epithelialization in wounds in human skin in vitro comparable to KCM. The study indicates that human keratinocytes produce a < 3 kDa peptide which may be partly responsible for the growth stimulatory and wound-healing properties of KCM.