Ca2+ regulation of gap junctional coupling in lens epithelial cells

Abstract

The quantitative effects of Ca2+signaling on gap junctional coupling in lens epithelial cells have been determined using either the spread of Mn2+ that is imaged by its ability to quench the fluorescence of fura 2 or the spread of the fluorescent dye Alexa Fluor 594. Gap junctional coupling was unaffected by a mechanically stimulated cell-to-cell Ca2+wave. Furthermore, when cytosolic Ca2+ concentration (Ca[Formula: see text]) increased after the addition of the agonist ATP, coupling was unaffected during the period that Ca[Formula: see text] was maximal. However, coupling decreased transiently ∼5–10 min after agonist addition when Ca[Formula: see text] returned to resting levels, indicating that this transient decrease in coupling was unlikely due to a direct action of Ca[Formula: see text] on gap junctions. An increase in Ca[Formula: see text] mediated by the ionophore ionomycin that was sustained for several minutes resulted in a more rapid and sustained decrease in coupling (IC50 ∼300 nM Ca2+, Hill coefficient of 4), indicating that an increase in Ca[Formula: see text]alone could regulate gap junctions. Thus Ca[Formula: see text]increases that occurred during agonist stimulation and cell-to-cell Ca2+ waves were too transient to mediate a sustained uncoupling of lens epithelial cells.