Evidence for KCNQ1 K⁺ channel expression in rat zymogen granule membranes and involvement in cholecystokinin-induced pancreatic acinar secretion

Abstract

Lee W-K, Torchalski B, Roussa E, Thévenod F. Evidence for KCNQ1 K ϩ channel expression in rat zymogen granule membranes and involvement in cholecystokinin-induced pancreatic acinar secretion. Am J Physiol Cell Physiol 294: C879-C892, 2008. First published January 23, 2008 doi:10.1152/ajpcell.00490.2007.-Secretion of enzymes and fluid induced by Ca 2ϩ in pancreatic acini is not completely understood and may involve activation of ion conductive pathways in zymogen granule (ZG) membranes. We hypothesized that a chromanol 293B-sensitive K ϩ conductance carried by a KCNQ1 protein is expressed in ZG membranes (ZGM). In suspensions of rat pancreatic ZG, ion flux was determined by ionophore-induced osmotic lysis of ZG suspended in isotonic salts. The KCNQ1 blocker 293B selectively blocked K ϩ permeability (IC50 of ϳ10 M). After incorporation of ZGM into planar bilayer membranes, cation channels were detected in 645/150 mM potassium gluconate cis/trans solutions. Channels had linear current-voltage relationships, a reversal potential (Erev) of Ϫ20.9 Ϯ 0.9 mV, and a single-channel K ϩ conductance (gK) of 265.8 Ϯ 44.0 pS (n ϭ 39). Replacement of cis 500 mM K ϩ by 500 mM Na ϩ shifted Erev to Ϫ2.4 Ϯ 3.6 mV (n ϭ 3), indicating K ϩ selectivity. Single-channel analysis identified several K ϩ channel groups with distinct channel behaviors. K ϩ channels with a gK of 651.8 Ϯ 88.0 pS, Erev of Ϫ22.9 Ϯ 2.2 mV, and open probability (Popen) of 0.43 Ϯ 0.06 at 0 mV (n ϭ 6) and channels with a gK of 155.0 Ϯ 11.4 pS, Erev of Ϫ18.3 Ϯ 1.8 mV, and Popen of 0.80 Ϯ 0.03 at 0 mV (n ϭ 3) were inhibited by 100 M 293B or by the more selective inhibitor HMR-1556 but not by the maxi-Ca 2ϩ -activated K ϩ

Chromanol 293B, an inhibitor of KCNQ1 channels, enhances glucose-stimulated insulin secretion and increases glucagon-like peptide-1 level in mice

“…19,20,26,27 By several GWA studies, KCNQ1 has been identified as a transethnic susceptibility gene for T2D. 6 Genetic variation in KCNQ1 appears to be associated with impaired insulin secretion.…”

Cellular Distribution and Subcellular Localization of mCLCA1/2 in Murine Gastrointestinal Epithelia

“…ZGs from mouse exocrine pancreas were isolated as described in detail elsewhere (Thévenod et al 2003;Lee et al 2008). Briefly, pancreatic tissue from female C57BL/6N mice (15-17 g, fasted overnight) (Charles River Laboratories; Sulzfeld, Germany) was homogenized by nitrogen pressure cavitation and centrifuged on a self-forming Percoll gradient.…”

Channels and Transporters in Zymogen Granule Membranes and their Role in Granule Function: Recent Progress and a Critical Assessment

“…These results appeared to oppose the role of Kv7.1 in enzyme secretion from permeabilized rat pancreatic acini described by us in the above study (63). However, we showed that CCK-stimulated enzyme secretion in permeabilized rat pancreatic acini was abolished only if flufenamate was applied together with 293B, which is an indication that several ZG cation channels with functional redundancy are involved in enzyme secretion (63). Lastly, this experiment resolves the controversy with the study on perfused rat pancreas (60) where no effect of Kv7.1 blockers on secretagogue-induced enzyme secretion had been observed.…”

“…They therefore concluded that Kv7.1 is not essential for secretagogue-mediated secretion of pancreatic acini. These results appeared to oppose the role of Kv7.1 in enzyme secretion from permeabilized rat pancreatic acini described by us in the above study (63). However, we showed that CCK-stimulated enzyme secretion in permeabilized rat pancreatic acini was abolished only if flufenamate was applied together with 293B, which is an indication that several ZG cation channels with functional redundancy are involved in enzyme secretion (63).…”