Carbachol activates a K+ channel of very small conductance in the basolateral membrane of rat pancreatic acinar cells.
Secretion of Cl- requires the presence of a K+ conductance to hyperpolarize the cell, and to provide the driving force for Cl- exit via luminal Cl- channels. In the exocrine pancreas Cl- secretion is mediated by an increase in cytosolic Ca2+ ([Ca2+]i). Two types of Ca2+-activated K+ channels could be shown in pancreatic acinar cells of different species. However, there are no data on Ca2+-activated K+ channels in rat pancreatic acini. Here we examine the basolateral K+ conductance of freshly isolated rat pancreatic acinar cells in cell-attached and cell-excised patch-clamp experiments. Addition of carbachol (CCH, 1 micromol/l) to the bath led to the activation of very small conductance K+ channels in cell-attached patches (n=27), producing a noisy macroscopic outward current. The respective outward conductance increased significantly by a factor of 2.1+/-0.1 (n=27). Noise analysis revealed a Lorentzian noise component with a corner frequency (f(c)) of 30.3+/-3.5 Hz (n=19), consistent with channel activity in these patches. The estimated single-channel conductance was 1.5+/-0.4 pS (n=19). In cell-excised patches (inside out) from cells previously stimulated with CCH, channel activity was only observed in the presence of K+ in the bath solution. Under these conditions f(c) was 47.6+/-11.9 Hz (estimated single-channel conductance 1.1+/-0.2 pS, n=20). The current/voltage relationship of the noise showed weak inward rectification and the reversal potential shifted towards E(K+) when Na+ in the bath was replaced by K+. Channel activity in cell-excised patches was slightly reduced by 10 mmol/l Ba2+ (23.6+/-2.1% of the total outward current) and was completely absent when K+ in the bath was replaced by Na+. Reduction of the [Ca2+]i from 1 mmol/l to 1 micromol/l in cell-excised experiments decreased the current by 52.3+/-12.3% (n=5). Expression of K(v)LQT1, one of the possible candidates for a small-conductance K+ channel in rat pancreatic acinar cells, was shown by reverse transcriptase polymerase chain reaction (RT-PCR). In fact, a K(V)LQT-blocker (chromanol 293B) reduced channel activity in seven excised patches. These data suggest that CCH activates very small conductance K+ channels in rat pancreatic acinar cells, most likely via an increase in [Ca2+]i.
Köttgen
M
M
Physiologisches Institut der Albert-Ludwigs-Universität Freiburg, Germany.
Hoefer
A
A
Kim
S J
SJ
Beschorner
U
U
Schreiber
R
R
Hug
M J
MJ
Greger
R
R
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D002462:Cell Membrane / Q000502:physiology*; D018679:Cholinergic Agonists / Q000494:pharmacology*; D004553:Electric Conductivity; D015870:Gene Expression; D010179:Pancreas / Q000648:ultrastructure*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology
D018679:Cholinergic Agonists; D015221:Potassium Channels; D001464:Barium; D012965:Sodium Chloride; D011189:Potassium Chloride; D002217:Carbachol; D002118:Calcium