Intracellular Cs+ activates the PKA pathway, revealing a fast, reversible, Ca2+-dependent inactivation of L-type Ca2+ current.
Inactivation of the L-type Ca2+ current (ICaL) was studied in isolated guinea pig ventricular myocytes with different ionic solutions. Under basal conditions, ICaL of 82% of cells infused with Cs+-based intracellular solutions showed enhanced amplitude with multiphasic decay and diastolic depolarization-induced facilitation. The characteristics of ICaL in this population of cells were not due to contamination by other currents or an artifact. These phenomena were reduced by ryanodine, caffeine, cyclopiazonic acid, the protein kinase A inhibitor H-89, and the cAMP-dependent protein kinase inhibitor. Forskolin and isoproterenol increased ICaL by only approximately 60% in these cells. Cells infused with either N-methyl-d-glucamine or K+-based intracellular solutions did not show multiphasic decay or facilitation under basal conditions. Isoproterenol increased ICaL by approximately 200% in these cells. In conclusion, we show that multiphasic inactivation of ICaL is due to Ca2+-dependent inactivation that is reversible on a time scale of tens of milliseconds. Cs+ seems to activate the cAMP-dependent protein kinase pathway when used as a substitute for K+ in the pipette solution.
Brette
Fabien
F
Centre National de la Recherche Scientifique Unité Mixte de Recherche 6542, Université de Tours, France. bmsfpb@bms.leeds.ac.uk
Lacampagne
Alain
A
Sallé
Laurent
L
Findlay
Ian
I
Le Guennec
Jean-Yves
JY
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology*; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D007424:Intracellular Fluid / Q000187:drug effects / Q000201:enzymology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D010766:Phosphorylation / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000099211:Phospholamban
D002118:Calcium; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D002586:Cesium; D017868:Cyclic AMP-Dependent Protein Kinases; D011188:Potassium; D019837:Ryanodine Receptor Calcium Release Channel; D000099211:Phospholamban