Protein kinase C mediates the inhibitory effect of substance P on HCO₃⁻ secretion from guinea pig pancreatic ducts

Abstract

Ϫ secretion may be physiologically important in terms of limiting the hydrostatic pressure developed within the ducts and in terms of switching off pancreatic secretion after a meal. Substance P (SP) inhibits secretin-stimulated HCO 3Ϫ secretion by modulating a Cl Ϫ -dependent HCO 3 Ϫ efflux step at the apical membrane of the duct cell (Hegyi P, Gray MA, and Argent BE. Am J Physiol Cell Physiol 285: C268 -C276, 2003). In the present study, we have shown that SP is present in periductal nerves within the guinea pig pancreas, that PKC mediates the effect of SP, and that SP inhibits an anion exchanger on the luminal membrane of the duct cell. Secretin (10 nM) stimulated HCO 3 Ϫ secretion by sealed, nonperfused, ducts about threefold, and this effect was totally inhibited by SP (20 nM). Phorbol 12,13-dibutyrate (PDBu; 100 nM), an activator of PKC, reduced basal HCO 3 Ϫ secretion by ϳ40% and totally blocked secretin-stimulated secretion. In addition, bisindolylmaleimide I (1 nM to 1 M), an inhibitor of PKC, relieved the inhibitory effect of SP on secretin-stimulated HCO 3 Ϫ secretion and also reversed the inhibitory effect of PDBu. Western blot analysis revealed that guinea pig pancreatic ducts express the ␣-, ␤ I-, ␦-, ⑀-, -, -, -, and -isoforms of PKC. In microperfused ducts, luminal H 2DIDS (0.5 mM) caused intracellular pH to alkalinize and, like SP, inhibited basal and secretinstimulated HCO 3 Ϫ secretion. SP did not inhibit secretion further when H 2DIDS was present in the lumen, suggesting that SP and H2DIDS both inhibit the activity of an anion exchanger on the luminal membrane of the duct cell.pancreas; Cl Ϫ /HCO 3 Ϫ exchanger; inhibition; epithelium THE PANCREATIC DUCTAL EPITHELIUM secretes an alkaline fluid that may contain up to 140 mM NaHCO 3 (4, 5). While the regulatory pathways that stimulate pancreatic ductal HCO 3 Ϫ secretion have been described well in the literature (4, 5), much less is known about inhibitory pathways. Such inhibitory pathways may be physiologically important in terms of limiting the hydrostatic pressure within the lumen of the duct (thus preventing leakage of enzymes into the parenchyma of the gland) and in terms of switching off pancreatic secretion after a meal (1). Both somatostatin (20, 32) and peptide YY (1, 34) have been shown to inhibit secretion from the intact pancreas and probably work by interfering with the neural and/or hormonal mechanisms that control the gland. In contrast, substance P (SP) (6, 18), 5-hydroxytryptamine (45), arginine vasopressin (29), and basolateral ATP (22) all have been shown to inhibit fluid and/or HCO 3 Ϫ secretion from isolated pancreatic ducts. Therefore, these agents must exert their effects directly on the ductal epithelium.SP has been identified in the pancreas of the dog, rat, and mouse (36), and the peptide has been shown to inhibit secretion from the intact gland of the dog (26, 31) and rat (27). Moreover, SP is a potent inhibitor of basal fluid secretion from isolated rat pancreatic ducts as well as of fluid secretion stimulated by secr...

Functional coupling of apical Cl−/HCO3− exchange with CFTR in stimulated HCO3− secretion by guinea pig interlobular pancreatic duct

“…3). H 2 DIDS similarly inhibited duct cell HCO 3 Ϫ efflux under basal conditions and in response to stimulation by secretin (12). H 2 DIDS inhibited both basal and secretin-stimulated fluid secretion into Cl Ϫ -rich luminal fluid (17 (35), but Slc26a3-mediated anion exchange with properties of V m sensitivity or electrogenicity was not observed by other laboratories (4,24,28).…”

Purinergic receptors in the endocrine and exocrine pancreas

“…In theory, the function of this P2Y 2 receptor to BK interaction would be the "brake" or "control" point in regulation of secretion in the ductal system, perhaps sensing and preventing distension of the duct. Other mediators, such as substance P and atrial natriuretic factor, have been ascribed similar protective roles since they inhibit duct secretion [108,109].…”

Regulation of anion exchanger Slc26a6 by protein kinase C

“…Inhibition by PKC was attributed to PKC-mediated displacement of carbonic anhydrase II from binding to SLC26A6 and consequent disruption of the HCO 3 transport metabolon (2). Inhibition of A6 by PKC may explain the observation that agonists acting through PKC inhibit HCO 3 secretion in the pancreas (13).…”