Ionomycin and pdbu increase mdck cell monolayer permeability
independent of an increase in myosin light chain phosphorylation.
Shasby, D. Michael, Jay M. Kamath, Alan B. Moy, and Sandra S. Shasby.
From the Department of Internal Medicine, University of Iowa
College of Medicine and the Veterans Administration Hospital, Iowa
City, IA.
APStracts 2:0075L, 1995.
It has been hypothesized that modulation of epithelial paracellular
permeability may be mediated by initiation of contraction of a band
of actin and myosin located at the tight junction. Phosphorylation of
myosin light chain (MLC) is an important determinant of acto-myosin
contraction. We asked if ionomycin (iono) and phorbol dibutyrate
(PDBU), which increase paracellular permeability of Madin Darby
Canine Kidney (MDCK) cell monolayers, increased MLC phosphorylation
in MDCK cells. MDCK cell MLC was constitutively phosphorylated by
myosin light chain kinase (MLCK), and after PDBU and ionomycin >
99% of MLC continued to be phosphorylated by MLCK. Neither iono, PDBU
nor the combination of iono and PDBU increased MLC phosphorylation.
In contrast, the phosphatase inhibitor, okadaic acid did increase MLC
phosphorylation. cAMP and forskolin decreased MLC phosphorylation in
control MDCK cells and in cells exposed to iono and PDBU. In
contrast, cAMP and forskolin did not blunt the decrease in
transepithelial resistance caused by iono and PDBU. Iono and PDBU
increase MDCK monolayer permeability independent of an increase in
MLC phosphorylation.
Received 14 November 1994; accepted in final form 21 March 1995.
APS Manuscript Number L323-4.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.