THE CHLORIDE TRANSPORT MECHANISM IN THE AVIAN (CHICK) PROXIMAL TUBULE: CFTR CHANNEL AND K+ CHANNEL
Date
2011-05
Authors
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Publisher
University of Delaware
Abstract
In this study, the functional expression of CFTR and the potassium channels, KCNQ1
and KCNN4, were assessed in the avian chick proximal tubule. A primary cell culture model was
developed and the apical expression of CFTR in this cell model was revealed using classic
electrophysiological methods. A basolateral-permeabilization approach was developed in the lab
to permeabilize the basolateral membrane so that the imposed chloride gradients could be
observed in this model under the influence of commercial inhibitors. It was found that
CFTR-Inh172 and GlyH-101, two CFTR inhibitors, both inhibit secretory chloride gradients
(basolateral to apical side). GlyH-101 was found to be the more effective inhibitor. In addition,
double inhibitor experiments and a multiple blocker experiment was conducted to examine the
expression of potassium channels on the basolateral membrane of the monolayers. In the double
inhibitor experiment, clotrimazole was added to either the basolateral side or apical side first, and
then added to the opposite side, to observe its effects on Forskolin-activated current. These
experiments revealed that clotrimazole, a selective calcium-activated potassium channel blocker,
is able to partially inhibit Forskolin-activated current in non-permeabilized monolayers of chick
proximal tubules. This suggests that calcium activated potassium channels exist in the proximal
tubule. As well, double inhibitor experiments revealed that clotrimazole had a more direct effect
on the current when administered to the apical side first. This further suggests that
calcium-activated potassium channels may exist on both apical and basolateral sides of the chick
proximal tubules.