科研之友
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摘要
ATP-sensitive K+ (K-ATP) channels couple the metabolic state of a cell to its electrical activity. They consist of a hetero-octameric complex with pore-forming Kir6.x (Kir6.1, Kir6.2) and regulatory sulfonylurea receptor (SUR) subunits. Functional data indicate that K-ATP channels contribute to epithelial K+ currents at colonic epithelia. However, their molecular identity and their properties are largely unknown. Therefore, changes in short-circuit current (I (sc)) induced by the K-ATP channel opener pinacidil (5 10(-4) mol l(-1)) were measured in Ussing chambers under control conditions and in the presence of different blockers of K-ATP channels. The channel subunits expressed by the colonic epithelium were identified by immunohistochemistry and by RT-PCR. The K+ channel opener, when administered at the serosal side, induced an increase in I (sc) consistent with the induction of transepithelial Cl- secretion after activation of basolateral K+ channels, whereas mucosal administration of pinacidil resulted in a negative I (sc). The increase in I (sc) evoked by serosal pinacidil was inhibited by serosal administration of glibenclamide (5 10(-4) mol l(-1)) and gliclazide (10(-6) mol l(-1)), but was resistant even against a high concentration (10(-2) mol l(-1)) of tolbutamide. In contrast, none of these inhibitors (administered at the mucosal side) reduced significantly the negative I (sc) induced by mucosal pinacidil. Instead, pinacidil inhibited Cl- currents across apical Cl- channels in basolaterally depolarized epithelia indicating that the negative I (sc) induced by mucosal pinacidil is due to a transient inhibition of Cl- secretion. In mRNA prepared from isolated colonic crypts, messenger RNA for both pore-forming subunits, Kir6.1 and Kir6.2, and two regulatory subunits (SUR1and SUR2B) was found. Expression within the colonic epithelium was confirmed for these subunits by immunohistochemistry. In consequence, K-ATP channels are present in the basolateral membrane of the colonic epithelium; their exact subunit composition, however, has still to be revealed.
- 出版日期2013-6
