Endogenous protein phosphatase 1 runs down gap junctional communication of rat ventricular myocytes.
Gap junctional channels are essential for normal cardiac impulse propagation. In ventricular myocytes of newborn rats, channel opening requires the presence of ATP to allow protein kinase activities; otherwise, channels are rapidly deactivated by the action of endogenous protein phosphatases (PPs). The lack of influence of Mg(2+) and of selective PP2B inhibition is not in favor of the involvements of Mg(2+)-dependent PP2C and PP2B, respectively, in the loss of channel activity. Okadaic acid (1 microM) and calyculin A (100 nM), both inhibitors of PP1 and PP2A activities, significantly retarded the loss of channel activity. However, a better preservation was obtained in the presence of selective PP1 inhibitors heparin (100 microg/ml) or protein phosphatase inhibitor 2 (I2; 100 nM). Conversely, the stimulation of endogenous PP1 activity by p-nitrophenyl phosphate, in the presence of ATP, led to a progressive fading of junctional currents unless I2 was simultaneously added. Together, these results suggest that a basal phosphorylation-dephosphorylation turnover regulates gap junctional communication which is rapidly deactivated by PP1 activity when the phosphorylation pathway is hindered.
Duthe
F
F
Physiologie Cellulaire, Unité Mixte de Recherche Centre National de Recherche Scientifique 6558, Université de Poitiers, 86022 Poitiers, France.
Plaisance
I
I
Sarrouilhe
D
D
Hervé
J C
JC
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology*; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017629:Gap Junctions / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D054645:Protein Phosphatase 1; D051381:Rats; D017208:Rats, Wistar; D016276:Ventricular Function
D004791:Enzyme Inhibitors; D047428:Protein Kinase Inhibitors; D016572:Cyclosporine; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D002118:Calcium