Cyclic AMP induces rapid increases in gap junction permeability and changes in the cellular distribution of connexin43.
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abstract
The rapid effects of cAMP on gap junction-mediated intercellular communication were examined in several cell types which express different levels of the gap junction protein, connexin43 (Cx43), including immortalized rat hepatocyte and granulosa cells, bovine coronary venular endothelial cells, primary rat myometrial and equine uterine epithelial cells. Functional analysis of changes in junctional communication induced by 8-bromo-cAMP was monitored by a fluorescence recovery after photobleaching assay in subconfluent cultures in the presence or absence of 1.0 mM 1-octanol (an agent which uncouples cells by closing gap junction channels). Communicating cells treated with 1.0 mM 8-bromo-cAMP alone exhibited significant increases in the percent of fluorescence recovery which were detected within 1-3 min depending on cell type, and junctional communication remained significantly elevated for up to 24 hr. Addition of 1.0 mM 8-bromo-cAMP to cultured cells, which were uncoupled with 1.0 mM octanol for 1 min, exhibited partial restoration of gap junctional permeability beginning within 3-5 min. Identical treatments were performed on cultures that were subsequently processed for indirect immunofluorescence to monitor Cx43 distribution. The changes in junctional permeability of cells correlated with changes in the distribution of immunoreactive Cx43. Cells treated for 2 hr with 10 microM monensin exhibited a reduced communication rate which was accompanied by increased vesicular cytoplasmic Cx43 staining and reduced punctate surface staining of junctional plaques. Addition of 1.0 mM 8-bromo-cAMP to these cultures had no effect on the rate of communication or the distribution of Cx43 compared to cultures treated with monensin alone. These data suggest that an effect of cyclic AMP on Cx43 gap junctions is to promote increases in gap junctional permeability by increasing trafficking and/or assembly of Cx43 to plasma membrane gap junctional plaques.
