Cells of the carotid body express connexin43 which is up-regulated by cAMP

We identified a gap junction protein subunit, connexin43 (Cx43) by immunofluorescence and immunoblotting, in cultured rat carotid body cells and in whole organs. In 1-week-old cultures, all cells were flat but after 3 h exposure to 8Br-cAMP (1 mM), tyrosine hydroxylase (TH) positive cells (chemoreceptors), but not TH negative cells, adopted a round body with multiple thin arborization processes. The incidence of dye coupling between cultured cells of the same type increased from 26% in controls to 73% after treatment with 8Br-cAMP. In control cultures, Cx43 immunoreactivity showed a diffuse perinuclear distribution and after 8Br-cAMP treatment, it was also found at cell-cell contacts. Both 8Br-cAMP-induced dye coupling and cellular redistribution of Cx43 were blocked by pretreatment with actinomycin D (5 microM), a mRNA transcription blocker. Moreover, 3 h exposure to 8Br-cAMP increased the levels of Cx43 in entire organs. We suggest that conditions that promote a sustained increase in cytosolic cAMP up-regulate coupling between carotid body cells in a transcription-dependent manner. The possible functional significance of these findings is discussed.