Effects of protein kinase inhibitors on canine Purkinje fibre pacemaker depolarization and the pacemaker current i(f).
1. The effects of the protein kinase inhibitors H-7 and H-8 were investigated on diastolic depolarization of the action potential with microelectrodes and on the pacemaker current if with the two-microelectrode voltage clamp in canine cardiac Purkinje fibres. 2. Both 200 microM-H-7 and 100 microM-H-8 had no significant effect on the slope of diastolic depolarization but eliminated the actions of isoprenaline (1 microM). 3. We examined the actions of H-7 and H-8 on if in the presence and absence of isoprenaline. H-7 (200 microM) shifted the pacemaker current if in the negative direction on the voltage axis, whereas 100 microM-H-8 had no significant effect by itself. Both 200 microM-H-7 and 100 microM-H-8 can reverse or prevent the actions of isoprenaline (1-5 microM) on if. 4. We applied activators of the cyclic AMP cascade down-stream to the beta-receptor, to further evaluate where H-7 and H-8 might be exerting their effects. When exposing Purkinje fibres to an adenylyl cyclase activator (forskolin, 10-50 microM), a phosphodiesterase inhibitor (IBMX, 100 microM) and a permeable cyclic AMP analogue (8-chlorophenylthio-cyclic AMP, 200 microM-1 mM), the amplitude of if was increased. H-7 and H-8 at 100-200 microM eliminated each of these actions. 5. These results suggest that a phosphorylation process is involved in the modulation of the pacemaker current, if, in Purkinje fibres. The different actions of H-7 and H-8 on basal if suggest the hypothesis that other protein kinases, possibly protein kinase C, might also be involved in regulating basal phosphorylation of if in Purkinje fibres.
Chang
F
F
Department of Physiology and Biophysics, SUNY, Stony Brook 11794-8661.
Cohen
I S
IS
DiFrancesco
D
D
Rosen
M R
MR
Tromba
C
C
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D004285:Dogs; D004594:Electrophysiology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology*; D007545:Isoproterenol / Q000037:antagonists & inhibitors; D007546:Isoquinolines / Q000494:pharmacology; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000502:physiology*; D011690:Purkinje Fibers / Q000502:physiology*
D007546:Isoquinolines; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D005576:Colforsin; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D011494:Protein Kinases; D011493:Protein Kinase C; D007545:Isoproterenol