title: Ionomycin and PDBU increase MDCK monolayer permeability independently of myosin light chain phosphorylation.
abstract: 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 actomyosin contraction. We asked if ionomycin (iono) and phorbol 12,13-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 iono > 99% of MLC continued to be phosphorylated by MLCK. Neither iono or PDBU, nor the combination of iono and PDBU, increased MLC phosphorylation. In contrast, the phosphatase inhibitor okadaic acid did increase MLC phosphorylation. Adenosine 3',5'-cyclic monophosphate (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 independently of an increase in MLC phosphorylation.
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Shasby
authors.forename: J M
authors.initials: JM
authors.lastname: Kamath
authors.forename: A B
authors.initials: AB
authors.lastname: Moy
authors.forename: S S
authors.initials: SS
authors.lastname: Shasby
mesh_terms: D000818:Animals; D002460:Cell Line; D055598:Chemical Phenomena; D002621:Chemistry; D000242:Cyclic AMP / Q000494:pharmacology; D004285:Dogs; D015759:Ionomycin / Q000494:pharmacology*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D009218:Myosins / Q000378:metabolism; D010539:Permeability / Q000187:drug effects; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D010766:Phosphorylation
chemical_list: D015240:Phorbol 12,13-Dibutyrate; D015759:Ionomycin; D000242:Cyclic AMP; D009218:Myosins