Voltage-dependent, slowly activating K+ current (I(Ks)) and its augmentation by carbachol in rat pancreatic acini.
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.
Kim
S J
SJ
Physiologisches Institut, Albert-Ludwigs Universität, Freiburg, Germany.
Greger
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology*; D002614:Chelating Agents / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology*; D003022:Clotrimazole / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D017629:Gap Junctions / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials; D010179:Pancreas / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology*; D051381:Rats
D002614:Chelating Agents; D018679:Cholinergic Agonists; D015221:Potassium Channels; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D002217:Carbachol; D003022:Clotrimazole; D002118:Calcium