Activation of Apical K+ Conductances by Muscarinic Receptor Stimulation in Rat Distal Colon: Fast and Slow Components

Activation of Apical K+ Conductances by Muscarinic Receptor Stimulation in Rat Distal Colon: Fast... In the epithelium of rat distal colon the acetylcholine analogue carbachol induces a transient increase of short-circuit current (I sc) via stimulation of cellular K+ conductances. Inhibition of the turnover of inositol-1,4,5-trisphosphate (IP3) by LiCl significantly reduced both the amplitude and the duration of this response. When the apical membrane was permeabilized with nystatin, LiCl nearly abolished the carbachol-induced activation of basolateral K+ conductances. In contrast, in epithelia, in which the basolateral membrane was bypassed by a basolateral depolarization, carbachol induced a biphasic increase in the K+ current across the apical membrane consisting of an early component carried by charybdotoxin- and tetraethylammonium-sensitive K+ channels followed by a sustained plateau carried by channels insensitive against these blockers. Only the latter was sensitive against LiCl or inhibition of protein kinases. In contrast, the stimulation of the early apical K+ conductance by carbachol proved to be resistant against inhibition of phospholipase C or protein kinases. However, apical dichlorobenzamil, an inhibitor of Na+/Ca2+ exchangers, or a Ca2+-free mucosal buffer solution significantly reduced the early component of the carbachol-induced apical K+ current. The presence of an apically localized Na+/Ca2+-exchanger was proven immunohistochemically. Taken together these experiments reveal divergent regulatory mechanisms for the stimulation of apical Ca2+-dependent K+ channels in this secretory epithelium, part of them being activated by an inflow of Ca2+ across the apical membrane. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Activation of Apical K+ Conductances by Muscarinic Receptor Stimulation in Rat Distal Colon: Fast and Slow Components

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Publisher
Springer-Verlag
Copyright
Copyright © 2003 by Springer-Verlag New York Inc.
Subject
Philosophy
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-003-0618-y
Publisher site
See Article on Publisher Site

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