Epithelial Barrier Resistance is Increased by the Divalent Cation Zinc in Cultured MDCKII Epithelial Monolayers

J Membrane Biol (2010) 237:115123 DOI 10.1007/s00232-010-9312-z

Epithelial Barrier Resistance is Increased by the Divalent Cation Zinc in Cultured MDCKII Epithelial Monolayers

Georgina Carr Jamie A. Wright

Nicholas L. Simmons

Received: 20 September 2010 / Accepted: 20 October 2010 / Published online: 6 November 2010 Springer Science+Business Media, LLC 2010

Abstract Topical zinc applications promote wound healing and epithelialization. Leaky MDCKII epithelia exposed to apical ZnCl2 (10 mM) showed a time-dependent increase (t0.5 22.2 2.7 min) of transepithelial resistance (Rt) from 82.3 2.4 X cm2 to 1,551 225.6 X cm2; the increase was dose-dependent, being observed at 3 mM but not at 1 mM. Basal Zn2? applications also increased epithelial resistance (at 10 mM to 323 225.6 X cm2). The linear currentvoltage relationship in control epithelia changed after apical 10 mM ZnCl2 to show rectication. Voltage deections resulting from inward currents showed time-dependent relaxation (basal potential difference (p.d.)-positive), with outward currents being time-independent. Cation selectivity was tested after apical ZnCl2 elevated resistance; both the NaCl:mannitol (basal replacement) dilution p.d. and the choline:Na bi-ionic p.d. decreased (PNa/PCl from 4.9 to 2.3 and PNa/Pcholine from 3.8 to 2.1, respectively). Transepithelial paracellular basal to apical 45Ca uxes increased approximately twofold when driven by a basal positive Na:NMDG bi-ionic p.d., but with basal 10 mM ZnCl2, 45Ca uxes decreased approximately twofold. Neither ZO-1 nor occludin distribution was altered after *2-h exposure to apical 10 mM ZnCl2.

However, claudin-2, though present at the tight junction, increased within the cell. Increased epithelial barrier resistance by Zn2? is due to modication of the paracellular pathway, most probably by multiple mechanisms.

Keywords Tight junction Madin-Darby canine

kidney cell Zinc Paracellular pathway Block

Introduction

Topical zinc applications provide the therapeutic benet of accelerated wound healing, with clinical evidence suggesting roles in autodebridgement, epithelial restitution and antimicrobial actions (Lansdown et al. 2007). Zinc oxide paste in dressing and bandages provides a depot for bio-available zinc concentrations, with constant levels of 13 mM being achieved that are nontoxic but high enough to promote wound healing (Lansdown et al. 2007). Recent studies have shown that extracellular Zn2? applied or released from injured tissue may act via a zinc receptor (GPR39) and MAP kinase activation, leading to keratinocyte migration and epithelial wound repair (Sharir et al. 2010).

Zinc...