Psoralens: novel modulators of cl- secretion.
Devor, Daniel C., Ashvani K. Singh, Robert J. Bridges, and Raymond A.
Frizzell.
Department of Cell Biology and Physiology, University of
Pittsburgh, Pittsburgh, PA 15261
APStracts 3:0329C, 1996.
We evaluated the effects of the psoralens on Cl- secretion (Isc)
across T84 monolayers. Methoxsalen failed to increase Isc on its own.
However, several observations suggest that the psoralens open cystic
fibrosis transmembrane conductance regulator (CFTR) Cl- channels.
First, following activation of the Ca2+-dependent basolateral
membrane K+ channel (KCa) by either 1-ethyl-2-benzimidazolinone (1
-EBIO) or thapsigargin, methoxsalen (10 (M) further increased Isc.
Second, when added prior to carbachol, methoxsalen potentiated the
Isc response to carbachol as predicted if it increased apical GCl.
Finally, following the establishment of a mucosa-to-serosa Cl-
gradient, and permeabilization of the basolateral membrane with
nystatin, the psoralens increased ICl, which was inhibited by
glibenclamide. In contrast, neither TS-TM calix[4]arene nor Cd2+,
inhibitors of outwardly-rectifying Cl- channels and the CIC-2 Cl-
channel, respectively, inhibited the psoralen-induced ICl. In
contrast to their effects on apical GCl, the psoralens failed to
significantly affect the basolateral membrane K+ conductance, GK;
subsequent addition of 1-EBIO induced a large increase in GK. Also,
in excised patches, methoxsalen failed to activate KCa. In addition
to potentiating the peak response to carbachol, the psoralens induced
a secondary, sustained response. Indeed, when added up to 60 minutes
following the return of the carbachol-induced Isc to baseline, the
psoralens induced a sustained Isc. This sustained response was
inhibited by atropine, demonstrating the requirement for continuous
muscarinic receptor activation by carbachol. This sustained response
was inhibited also by verapamil, removal of bath Ca2+, and
charybdotoxin (CTX). These results suggest that the return of ISC to
baseline after carbachol stimulation is not due to down-regulation of
Ca2+ influx or KCa. Finally, we obtained similar results with the
psoralens in both rat colon and primary cultures of murine tracheal
epithelium. Based on these observations, we conclude that the
psoralens represent a novel class of Cl- channel openers which can be
used to probe the mechanisms underlying Ca2+-mediated Cl- secretion.
Received 22 July 1996; accepted in final form 4 October 1996.
APS Manuscript Number C404-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996