Evidence for KCNQ1 K+ channel expression in rat zymogen granule membranes and involvement in cholecystokinin-induced pancreatic acinar secretion.
Secretion of enzymes and fluid induced by Ca(2+) 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(+) 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(+) permeability (IC(50) of approximately 10 microM). 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 (E(rev)) of -20.9 +/- 0.9 mV, and a single-channel K(+) conductance (g(K)) of 265.8 +/- 44.0 pS (n = 39). Replacement of cis 500 mM K(+) by 500 mM Na(+) shifted E(rev) to -2.4 +/- 3.6 mV (n = 3), indicating K(+) selectivity. Single-channel analysis identified several K(+) channel groups with distinct channel behaviors. K(+) channels with a g(K) of 651.8 +/- 88.0 pS, E(rev) of -22.9 +/- 2.2 mV, and open probability (P(open)) of 0.43 +/- 0.06 at 0 mV (n = 6) and channels with a g(K) of 155.0 +/- 11.4 pS, E(rev) of -18.3 +/- 1.8 mV, and P(open) of 0.80 +/- 0.03 at 0 mV (n = 3) were inhibited by 100 microM 293B or by the more selective inhibitor HMR-1556 but not by the maxi-Ca(2+)-activated K(+) channel (BK channel) inhibitor charybdotoxin (5 nM). KCNQ1 protein was demonstrated by immunoperoxidase labeling of pancreatic tissue, immunogold labeling of ZG, and immunoblotting of ZGM. 293B also inhibited cholecystokinin-induced amylase secretion of permeabilized acini (IC(50) of approximately 10 microM). Thus KCNQ1 may account for ZG K(+) conductance and contribute to pancreatic hormone-stimulated enzyme and fluid secretion.
Lee
Wing-Kee
WK
Department of Physiology & Pathophysiology, University of Witten/Herdecke, Witten, Germany.
Torchalski
Blazej
B
Roussa
Eleni
E
Thévenod
Frank
F
D000681:Amylases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002756:Cholagogues and Choleretics / Q000494:pharmacology; D002766:Cholecystokinin / Q000494:pharmacology*; D002839:Chromans / Q000494:pharmacology; D004792:Enzyme Precursors; D005786:Gene Expression Regulation / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D051657:KCNQ1 Potassium Channel / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008297:Male; D010179:Pancreas / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D022142:Secretory Vesicles / Q000201:enzymology / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology
D002756:Cholagogues and Choleretics; D002839:Chromans; D004792:Enzyme Precursors; D051657:KCNQ1 Potassium Channel; C496911:Kcnq1 protein, rat; D013449:Sulfonamides; C103474:6-cyano-4-(N-ethylsulfonyl-N-methylamino)-3-hydroxy-2,2-dimethylchromane; D002766:Cholecystokinin; D000681:Amylases