SLC26 transporters and the inhibitory control of pancreatic ductal bicarbonate secretion

Abstract

SLC26 anion exchangers (probably SLC26A3 and SLC26A6) are expressed on the apical membrane of pancreatic duct cells and play a key role in HCO3- secretion; a process that is inhibited by the neuropeptide, substance P (SP). SP had no effect on basolateral HCO3- transporters in the duct cell or on CFTR Cl- channels, but inhibited a Cl- -dependent HCO3- efflux step on the apical membrane. In microperfused ducts, luminal H2DIDS (0.5mM) caused intracellular pH to alkalinize (consistent with inhibition of HCO3- efflux) and, like SP, inhibited HCO3- secretion. SP did not reduce HCO3- secretion further when H2DIDS was applied to the duct lumen, suggesting that SP and H2DIDS inhibit the same transporter on the apical membrane. As SLC26A6 is DIDS-sensitive, this isoform is the likely target for SP. The inhibitory effect of SP was mimicked by phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C (PKC). Moreover, bisindolylmaleimide, a blocker of PKC, relieved the inhibitory effect of both SP and PDBu on HCO3- secretion. Western blot analysis revealed that guinea pig pancreatic ducts express the alpha, beta1, delta, epsilon, eta, theta, zeta and mu isoforms o f PKC. We conclude that PKC is a negative regulator of SLC26 activity in pancreatic duct cells.