CYCLIC-AMP INDUCES RAPID INCREASES IN GAP JUNCTION PERMEABILITY AND CHANGES IN THE CELLULAR-DISTRIBUTION OF CONNEXIN43

The rapid effects of cAMP on gap junction-mediated intercellular commu nication were examined in several cell types which express different l evels of the gap junction protein, connexin43 (Cx43), including immort alized rat hepatocyte and granulosa cells, bovine coronary venular end othelial cells, primary rat myometrial and equine uterine epithelial c ells. Functional analysis of changes in junctional communication induc ed by 8-bromo-cAMP was monitored by a fluorescence recovery after phot obleaching assay in subconfluent cultures in the presence or absence o f 1.0 mM l-octanol (an agent which uncouples cells by closing gap junc tion channels). Communicating cells treated with 1.0 mM 8-bromo-cAMP a lone exhibited significant increases in the percent of fluorescence re covery 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 unco upled with 1.0 mM octanol for 1 min, exhibited partial restoration of gap junctional permeability beginning within 3-5 min. Identical treatm ents were performed on cultures that were subsequently processed for i ndirect immunofluorescence to monitor Cx43 distribution. The changes i n junctional permeability of cells correlated with changes in the dist ribution of immunoreactive Cx43. Cells treated far 2 hr with 10 mu M m onensin exhibited a reduced communication rate which was accompanied b y increased vesicular cytoplasmic Cx43 staining and reduced punctate s urface 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 d istribution 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 t rafficking and/or assembly of Cx43 to plasma membrane gap junctional p laques.