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Gap junction channels exhibit connexin-specific permeability to cyclic nucleotides.

Kanaporis G, Mese G, Valiuniene L, White TW, Brink PR, Valiunas V - J. Gen. Physiol. (2008)

Bottom Line: However, homotypic Cx40 and homotypic Cx26 exhibited reduced cAMP permeability in comparison to Cx43.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA.

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 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.

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Selectivity properties of Cx43, Cx40, and Cx26 to various solutes relative to K+. The bars represent Na+/K+, cAMP/K+, and LY/ K+ ratios plotted on log scale for Cx43 (white bar), Cx26 (gray bar), and Cx40 (black bar).
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fig8: Selectivity properties of Cx43, Cx40, and Cx26 to various solutes relative to K+. The bars represent Na+/K+, cAMP/K+, and LY/ K+ ratios plotted on log scale for Cx43 (white bar), Cx26 (gray bar), and Cx40 (black bar).

Mentions: Fig. 8 compares the selectivity properties of Cx43, Cx40, and Cx26 to various solutes relative to K+ ions. The bars represent cAMP/K+, LY/K+ (Valiunas et al., 2002), and Na+/K+ ratios plotted on log scale for Cx43 (white bar), Cx26 (gray bar), and Cx40 (black bar). All three homotypic channels are poorly selective toward monovalent cations as illustrated by the Na+/K+ conductance ratios. The Na+/K+ unitary conductance ratios were determined by comparison of unitary conductance in NaCl and KCl solutions (Beblo and Veenstra, 1997; Wang and Veenstra, 1997) for Cx43 and Cx40 and the data for Cx26 is derived from Fig. 7. Interestingly, both LY and cAMP showed a similar permeability order: Cx43 > Cx26 ≥ Cx40, suggesting that these channels have distinct selectivity for larger solutes.


Gap junction channels exhibit connexin-specific permeability to cyclic nucleotides.

Kanaporis G, Mese G, Valiuniene L, White TW, Brink PR, Valiunas V - J. Gen. Physiol. (2008)

Selectivity properties of Cx43, Cx40, and Cx26 to various solutes relative to K+. The bars represent Na+/K+, cAMP/K+, and LY/ K+ ratios plotted on log scale for Cx43 (white bar), Cx26 (gray bar), and Cx40 (black bar).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2279171&req=5

fig8: Selectivity properties of Cx43, Cx40, and Cx26 to various solutes relative to K+. The bars represent Na+/K+, cAMP/K+, and LY/ K+ ratios plotted on log scale for Cx43 (white bar), Cx26 (gray bar), and Cx40 (black bar).
Mentions: Fig. 8 compares the selectivity properties of Cx43, Cx40, and Cx26 to various solutes relative to K+ ions. The bars represent cAMP/K+, LY/K+ (Valiunas et al., 2002), and Na+/K+ ratios plotted on log scale for Cx43 (white bar), Cx26 (gray bar), and Cx40 (black bar). All three homotypic channels are poorly selective toward monovalent cations as illustrated by the Na+/K+ conductance ratios. The Na+/K+ unitary conductance ratios were determined by comparison of unitary conductance in NaCl and KCl solutions (Beblo and Veenstra, 1997; Wang and Veenstra, 1997) for Cx43 and Cx40 and the data for Cx26 is derived from Fig. 7. Interestingly, both LY and cAMP showed a similar permeability order: Cx43 > Cx26 ≥ Cx40, suggesting that these channels have distinct selectivity for larger solutes.

Bottom Line: However, homotypic Cx40 and homotypic Cx26 exhibited reduced cAMP permeability in comparison to Cx43.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA.

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 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.

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