Substance P inhibits pancreatic ductal HCO3-secretion via activation of protein kinase C in guinea pig

Abstract

Background. The inhibitory control of pancreatic ductal HCO3- 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 HCO3- secretion by modulating a Cl–dependent HCO3-efflux step at the apical membrane of the duct cell (Hegyi et al. Am J Physiol Cell Physiol 285: C268-C276, 2003). In the present study we have sought to localise SP in the guinea-pig pancreas and to identify the intracellular signalling pathway utilised by SP. Methods. Small intra/interlobular pancreatic ducts were isolated from guinea pigs. The rate of HCO3-secretion was determined from intracellular pH measurements as previously described (Hegyi et al., 2003). Western blot analysis was used to identify PKC isoforms expressed in the isolated ducts and immunohistochemistry to localize SP in the pancreas. Results. Our results show that SP is present in periductal nerves within the guinea-pig pancreas and that protein kinase C (PKC) mediates the effect of SP. Secretin (10 nM) stimulated HCO3- secretion by sealed, non-perfused, ducts about 3 fold and this effect was totally inhibited by SP (20 nM). Phorbol 12, 13-dibutyrate (PDBu; 100 nM), an activator of PKC, reduced basal HCO3- secretion by about 40%, and totally blocked secretin-stimulated secretion. In addition, bisindolylmaleimide I (1 nM to 1µM), an inhibitor of PKC, relieved the inhibitory effect of SP on secretin-stimulated HCO3- secretion. Western blot analysis revealed that guinea pig pancreatic ducts express the alfa, -betaI, -delta, -epsilon, -eta, -theta, -zeta and -mu isoforms of PKC. Conclusions. Taken together, our results indicate that SP reduces HCO3- secretion in guinea pig ducts via activation of PKC, which inhibits a luminal Cl-/HCO3- exchanger (most likely a member of the SLC26 family). This work was supported by The Wellcome Trust and OTKA.