Voltage-dependent, slowly activating K + current ( I Ks ) and its augmentation by carbachol in rat pancreatic acini

Abstract

Acetylcholine-stimulated exocrine secretion of Cl- and water requires the concomitant activation of K+ channels. However, there has not been much investigation of the carbachol- (CCH-) activated K+ channel of rodent pancreatic acini. Here, in a study of rat pancreatic acini, we characterize a voltage-dependent, slowly activating outward current (I(Ks)) that is augmented by CCH. Intact acini were obtained by enzymatic digestion and fast-whole-cell patch-clamp was applied. With symmetrical [Cl-] (32 mmol/l) in the pipette and bath solution, acinar cells had resting membrane voltages of -45+/-0.8 mV (n=97) under current-clamp conditions. CCH (10 micromol/l), which is known to activate Cl- channels via a Ca2+-mediated pathway, sharply depolarized the membrane to -4+/-0.5 mV, which was more negative than E(Cl) (0 mV), and reversed it to -41+/-0.9 mV (n=83) by washout. A clamp voltage of 0 mV activated I(Ks) under control conditions (91+/-8.6 pA, n=83). During CCH application an increase of outward current was observed at 0 mV, and at -50 mV a marked increase of inward Cl current occurred. In the presence of CCH the slow activation of I(Ks) was rarely distinguishable because of interference by the huge Cl- conductance. During CCH washout and decrease of inward current, a persistent augmentation of I(Ks) was revealed (486+/-36.3 pA, n=83). I(Ks) and its augmentation were abolished by substituting K+ in the pipette solution with Cs+. Augmentation of I(Ks) was mimicked by applying ionomycin (0.1 micromol/l), a Ca2+ ionophore. Pharmacological blockers were tested. The chromanol 293B and clotrimazole blocked I(Ks) at micromolar concentrations (IC50=3 micromol/l and 9 micromol/l, respectively) and Ba2+ was a poor blocker (IC50=3 mmol/l). In the presence of CCH (0.2 micromol/l), the membrane was depolarized to around -20 mV and the addition of 293B (10 micromol/l) further depolarized the membrane by 11+/-3 mV (n=5). These data suggest the presence of I(Ks) channels in rat pancreatic acini and their muscarinic activation.

Molecular basis of potassium channels in pancreatic duct epithelial cells

“…K i values for K v 7.1/KCNE1, K v 7.1/KCNE2 and K v 7.1/KCNE3 were 3–10 μM, 0.4 μM, and 3–4 μM, respectively 68 , 70 , 82 , 86 , 87 . Voltage-gated K + currents in pancreatic acinar cells were shown to be inhibited by chromanol 293B with a K i value of 3 μM 72 . This result supports voltage-gated K + channels being composed of K v 7.1 and KCNE1 β-subunit in acinar cells.…”

“…Functional expression of the KCNQ1 gene has also been demonstrated in the kidney, stomach, small intestine, colon, 68 - 71 pancreatic acini, 69 , 72 , 73 and pancreatic ducts 13 . Immunoreactivity of the K v 7.1 protein was reported in the parietal cells of the stomach, in the basolateral membrane of small intestinal and colonic crypt cells, 69 , 74 , 75 and in acinar and duct cells of the pancreas 13 , 69 .…”

Cyclic AMP-Dependent Regulation of Kv7 Voltage-Gated Potassium Channels

“…In the heart, Kv7.1 associates with the ancillary subunit KCNE1 to constitute the channel responsible for the late repolarizing current termed I Ks (Barhanin et al, 1996;Sanguinetti et al, 1996). Kv7.1 also associates with KCNE1 in the inner ear, where they regulate auditory function and pancreatic acinar cells where activation of the Kv7.1-KCNE1 channel provides the driving force for Cl − secretion (Kim and Greger, 1999;Köttgen et al, 1999;Warth et al, 2002). In addition, Kv7.1 channels in the pancreatic ß-cells contribute to the regulation of insulin secretion, and loss of function mutations in the KCNQ1 gene leads to impaired ß-cell insulin secretion, which is associated with type 2 diabetes (Ullrich et al, 2005;Unoki et al, 2008;Yasuda et al, 2008;Yamagata et al, 2011;Liu et al, 2014;Torekov et al, 2014;Min Lee et al, 2017;Zhang et al, 2020).…”

Ion Channel Signature in Healthy Pancreas and Pancreatic Ductal Adenocarcinoma

“…KCNQ1 (KVLQT1, Kv7.1) and KCNE1 (IsK, minK) have been found in abundance in pancreatic acinar cells ( Kottgen et al, 1999 ; Bleich and Warth, 2000 ; Demolombe et al, 2001 ; Warth and Barhanin, 2002 ; Warth et al, 2002 ; Hayashi et al, 2012 ). By using mouse models associated with electrophysiological studies, Warth et al (2002) showed that KCNQ1 was predominantly located at the basolateral membrane and its co-assemblage with KCNE1 leads to a voltage-dependent K + current that was increased by cholinergic stimulation and inhibited by the KCNQ1 blocker ( Kim and Greger, 1999 ; Kottgen et al, 1999 ; Warth et al, 2002 ). The fact that inhibition of KCNQ1 channels diminishes intestinal Cl - secretion, made the authors suggest its involvement in pancreatic electrolyte secretion process.…”