Ca2+ regulation of tight-junction permeability and structure in Necturus gallbladder

Abstract

To explore the role of Ca2+ in tight-junction permeability, the Necturus gallbladder was exposed to varying Ca2+ concentrations and to the Ca2+ ionophore A23187 added to the mucosal side (1.9 X 10(-6) to 6.8 X 10(-5) M). Electrophysiological parameters measured in an Ussing-type chamber were correlated with tight-junction morphology revealed by freeze-fracture electron microscopy. In Ca2+-free bathing media, transepithelial resistance decreases and tight-junctional ultrastructure is fragmented. In 1.8 mM Ca2+ media, A23187 induces an initial drop in transepithelial resistance, followed by an increase in transepithelial resistance to a value 20% above base line. At peak response to A23187, NaCl diffusion potentials decrease. Freeze-fracture replicas reveal that the number of junctional strands increase pari passu with junctional depth. Both physiological and morphological changes were partially reversible. The initial decrease in transepithelial resistance coincided with a persistent hyperpolarization of the mucosal cell membrane potential difference and a decrease in the mucosal-to-serosal cell membrane resistance ratio. Thus A23187 alters both the transcellular and paracellular pathway, resulting in opposing effects on transepithelial resistance.

Regulation of the dynamic localization of the rat Bsep gene-encoded bile salt export pump by anisoosmolarity

“…58 This was also found in the present study when cholestasis was induced by Ca 2ϩ withdrawal (Fig. 6), a condition that was attributed by most, 51,52,53,[59][60][61][62][63][64] but not all 65 investigators to a disruption of the tight junctional permeability barrier. Whereas Ca 2ϩ -free conditions induced cholestasis within 5 minutes, disruption of the continuous occludin staining and occludin internalization, no effect was found on the localization of Mrp2 and Bsep.…”

“…[41][42][43][44][45][46][47][48][49][50] In cultured primary cells and tissue (e.g., pancreatic acinar cells, Necturnus gallbladder) Ca 2ϩ -depletion led to an increase of transepithelial resistance and increased paracellular permeability. 51,52 Ca 2ϩ -free perfusion of the isolated perfused rat liver results in rapid and almost complete cessation of bile flow. 53 Thus, another aim of this study was to determine morphologically whether osmoregulation of the tight junction complex occurs and Ca 2ϩ -free conditions served as a positive control for tight junctions disruption.…”

Activation of the calcium-sensing receptor induces deposition of tight junction components to the epithelial cell plasma membrane

“…TJs regulate the passage of ions and small molecules through the paracellular pathway (Van Itallie and Anderson, 2004), and also restrict the diffusion of membrane proteins between the apical and basolateral compartments (van Meer and Simons, 1986). Extracellular Ca 2+ is essential for both the development of new junctions (Cereijido et al, 1981;Gonzalez-Mariscal et al, 1985;Martinez-Palomo et al, 1980) and the stabilization of mature junctions (Galli et al, 1976;Hays et al, 1965;Meldolesi et al, 1978;Palant et al, 1983;Sedar and Forte, 1964) between epithelial cells. The dependence of TJ assembly on Ca 2+ is probably attributable to the capacity of Ca 2+ to stabilize the cell adhesion molecule E-cadherin in its adhesive state at AJs (Boller et al, 1985;Ringwald et al, 1987).…”

Loosening tight junctions. Lessons from the intestine.

“…Examples include experimentally induced alteration in ZO subunit number (number of strands/kisses) (8,(24)(25)(26)(27), and alteration in surface charge within the pores of the ZO as suggested by altered ZO charge selectivity (28). Recent work using two strains of MDCK cells which have either high (-3,000 Q cm2) or low (-100 Q cm2) resistance suggests that in this case the basis of the difference in resistance observed is not due to strain-related differences in ZO subunit number (29).…”