Gap junction channels exhibit connexin-specific permeability to cyclic nucleotides.
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 approximately 10 to 7 times more permeable to cAMP than Cx40 or Cx26 (Cx43 > Cx26 > or = 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.
Kanaporis
Giedrius
G
Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA.
Mese
Gulistan
G
Valiuniene
Laima
L
White
Thomas W
TW
Brink
Peter R
PR
Valiunas
Virginijus
V
D002450:Cell Communication / Q000502:physiology; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability / Q000502:physiology; D000072259:Connexin 26; D018031:Connexin 43 / Q000737:chemistry / Q000378:metabolism; D017630:Connexins / Q000737:chemistry / Q000378:metabolism; D000242:Cyclic AMP / Q000737:chemistry / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000378:metabolism; D004058:Diffusion; D004553:Electric Conductivity; D017629:Gap Junctions / Q000737:chemistry* / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010539:Permeability; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D000097003:Gap Junction alpha-5 Protein
D000072259:Connexin 26; D018031:Connexin 43; D017630:Connexins; D000242:Cyclic AMP; D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015221:Potassium Channels; D000097003:Gap Junction alpha-5 Protein; C000607042:GJB2 protein, human