Apical electrolyte concentration modulates barrier function and tight junction protein localization in bovine mammary epithelium

Abstract

Quesnell RR, Erickson J, Schultz BD. Apical electrolyte concentration modulates barrier function and tight junction protein localization in bovine mammary epithelium. Am J Physiol Cell Physiol 292: C305-C318, 2007. First published August 2, 2006; doi:10.1152/ajpcell.00567.2005In vitro mammary epithelial cell models typically fail to form a consistently tight barrier that can effectively separate blood from milk. Our hypothesis was that mammary epithelial barrier function would be affected by changes in luminal ion concentration and inflammatory cytokines. Bovine mammary epithelial (BME-UV cell line) cells were grown to confluence on permeable supports with a standard basolateral medium and either high-electrolyte (H-elec) or low-electrolyte (L-elec) apical medium for 14 days. Apical media were changed to/from H-elec medium at predetermined times prior to assay. Transepithelial electrical resistance (R te) was highest in monolayers continuously exposed to apical L-elec. A time-dependent decline in R te began within 24 h of H-elec medium exposure. Change from H-elec medium to L-elec medium time-dependently increased R te. Permeation by FITC-conjugated dextran was elevated across monolayers exposed to H-elec, suggesting compromise of a paracellular pathway. Significant alteration in occludin distribution was evident, concomitant with the changes in R te, although total occludin was unchanged. Neither substitution of Na ϩ with N-methyl-Dglucosamine (NMDG ϩ ) nor pharmacological inhibition of transcellular Na ϩ transport pathways abrogated the effects of apical H-elec medium on R te. Tumor necrosis factor alpha, but not interleukin-1␤ nor interleukin-6, in the apical compartment caused a significant decrease in R te within 8 h. These results indicate that mammary epithelium is a dynamic barrier whose cell-cell contacts are acutely modulated by cytokines and luminal electrolyte environment. Results not only demonstrate that BME-UV cells are a model system representative of mammary epithelium but also provide critical information that can be applied to other mammary model systems to improve their physiological relevance.

Hydration status affects urea transport across rat urothelia

“…Tight junction proteins, including zona occluden-1, occludin, and claudin-4, -8, and -12, have recently been described in bladder epithelial cells (1). Since in other epithelial cells claudins have been reported to be acutely physiologically regulated (3,4,34,46), it is possible that they, or other urothelial tight junction proteins might be regulated by hydration status. In this regard, prior studies have demonstrated dehydration-induced changes in renal collecting duct paracellular pathways resulting in higher permeability to water and nonelectrolytes (10) as well as altered rat renal papillary and renal pelvis epithelia (known to be similar in appearance and function to lower urinary tract epithelia) morphology in antidiuresis (5).…”

Tumor necrosis factor alpha increases epithelial barrier permeability by disrupting tight junctions in Caco-2 cells

“…Most studies showed that TNF-α had no effect on the expression of the occludin protein (34)(35)(36), whereas others found that TNF-α or a mixture of cytokines (TNF-α, interferon-γ, interleukin-1β) reduced the amount and expression of occludin (30,37,38). In our study, TNF-α changed the expression of the special phosphorylated occludin protein in Caco-2 cells, supporting the conclusion that TNF-α can affect the expression of TJ proteins, disrupt the TJs and increase the permeability of the intestinal barrier.…”

Contribution of KCNQ1 to the regulatory volume decrease in the human mammary epithelial cell line MCF-7

“…To date, investigations into fundamental aspects of mammary epithelial physiology have utilized mouse (5,6) and bovine (41) cell lines. Such studies have determined that fluid secretion across the apical membrane of murine mammary epithelial cells could be stimulated by inhibition of the epithelial Na ϩ channel or activation of the cystic fibrosis transmembrane conductance regulator Cl Ϫ channel (5) or Ca 2ϩ -dependent Cl Ϫ channels coupled to P2Y 2 purinoceptors (6).…”

“…Such studies have determined that fluid secretion across the apical membrane of murine mammary epithelial cells could be stimulated by inhibition of the epithelial Na ϩ channel or activation of the cystic fibrosis transmembrane conductance regulator Cl Ϫ channel (5) or Ca 2ϩ -dependent Cl Ϫ channels coupled to P2Y 2 purinoceptors (6). More recently, the work of Quesnell et al (41) demonstrated that the electrolyte composition at the apical membrane of bovine mammary epithelial cells has profound effects on the distribution of the tight junction protein occludin. Thus these models demonstrate the complex and dynamic nature of transepithelial transport across the mammary epithelial barrier.…”