Gap Junction Channels Exhibit Connexin-specific Permeability to Cyclic Nucleotides

Abstract

Gap junction channels exhibit connexin dependent biophysical properties, including selective intercellular passage of larger solutes, such as second messengers and siRNA. Here, we report the determination of cyclic nucleotide (cAMP) permeability through gap junction channels composed of Cx43, Cx40, or Cx26 using simultaneous measurements of junctional conductance and intercellular transfer of cAMP. For cAMP detection the recipient cells were transfected with a reporter gene, the cyclic nucleotide-modulated channel from sea urchin sperm (SpIH). cAMP was introduced via patch pipette into the cell of the pair that did not express SpIH. SpIH-derived currents (I h) were recorded from the other cell of a pair that expressed SpIH. cAMP diffusion through gap junction channels to the neighboring SpIH-transfected cell resulted in a five to sixfold increase in I h current over time. Cyclic AMP transfer was observed for homotypic Cx43 channels over a wide range of conductances. However, homotypic Cx40 and homotypic Cx26 exhibited reduced cAMP permeability in comparison to Cx43. The cAMP/K+ permeability ratios were 0.18, 0.027, and 0.018 for Cx43, Cx26, and Cx40, respectively. Cx43 channels were ∼10 to 7 times more permeable to cAMP than Cx40 or Cx26 (Cx43 > Cx26 ≥ Cx40), suggesting that these channels have distinctly different selectivity for negatively charged larger solutes involved in metabolic/biochemical coupling. These data suggest that Cx43 permeability to cAMP results in a rapid delivery of cAMP from cell to cell in sufficient quantity before degradation by phosphodiesterase to trigger relevant intracellular responses. The data also suggest that the reduced permeability of Cx26 and Cx40 might compromise their ability to deliver cAMP rapidly enough to cause functional changes in a recipient cell.

Gap junctions between regulatory T cells and dendritic cells prevent sensitization of CD8+ T cells

“…[37][38][39] These messengers regulate the adhesion and transendothelial diapedesis of leukocytes during inflammatory reactions. 40,41 In particular, ATP derivates might be important because it has recently been shown that Treg cells augment adenosine levels in vivo and in vitro, leading to suppression of effector T-cell proliferation.…”

Connexins and gap junctions in the EDHF phenomenon and conducted vasomotor responses

“…Measurements of [cAMP] levels in the effluent from buffer-perfused rabbit and rat vascular beds have shown that ACh and the SERCA inhibitor cyclopiazonic acid both stimulate prostanoid-independent efflux of cAMP from the endothelium [97,182]. Collectively, these observations suggest that smooth muscle cAMP levels might in part reflect diffusion of endothelium-derived cAMP into the arterial media via myoendothelial gap junctions containing Cx43 or Cx40 [99]. Candidate pathways leading to activation of endothelial adenylyl cyclase include (1) the formation of eicosanoids from arachidonic acid (see below) and (2) activation of specific Ca 2+ -stimulated isoforms of adenylyl cyclase (e.g., type 8) by store-operated Ca 2+ entry which can reflect the co-localization of this isoenzyme with store-operated Ca 2+ channels in membrane caveolae [194].…”

Gap junctional intercellular communication in the juxtaglomerular apparatus

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