Cardiac gap junctions: three distinct single channel conductances and their modulation by phosphorylating treatments.
The effects of an increase in intracellular cyclic GMP (cGMP)-concentration on gap junctional current (Ij) were studied in cultured neonatal rat heart cells using both the whole-cell and perforated patch voltage-clamp method. In whole-cell measurements, exposure to 8-bromo-cGMP or carbachol reduced Ij. With the perforated patch technique, on the other hand, Ij was not affected by either 8-bromo-cGMP or carbachol. Addition of alkaline phosphatase prevented the carbachol-induced decrease in Ij in whole-cell measurements. Reduction of Ij in well-coupled cell pairs by application of heptanol allowed us to study the effects of these substances on the single gap junction channel level. We found that cGMP-treatment shifts the single channel conductance (gamma j) from 43 to 21 pS in whole-cell measurements and that intracellular addition of phosphatase prevents this shift. In contrast, intracellular phosphatase-treatment itself shifts gamma j to 70 pS. Our results indicate that Cx43-gap junction channels may exhibit three conductance levels (21 pS, 40-45 pS and 70 pS), depending on the phosphorylation state of the protein.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000469:Alkaline Phosphatase / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002217:Carbachol / Q000494:pharmacology; D004553:Electric Conductivity; D007365:Intercellular Junctions / Q000378:metabolism / Q000502:physiology*; D007473:Ion Channels / Q000378:metabolism / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats
D007473:Ion Channels; D015124:8-Bromo Cyclic Adenosine Monophosphate; D002217:Carbachol; D000469:Alkaline Phosphatase