Effects of β-adrenoceptor stimulation on delayed rectifier K(+) currents in canine ventricular cardiomyocytes.
OBJECTIVE
While the slow delayed rectifier K(+) current (I(Ks)) is known to be enhanced by the stimulation of β-adrenoceptors in several mammalian species, phosphorylation-dependent regulation of the rapid delayed rectifier K(+) current (I(Kr)) is controversial.


METHODS
In the present study, therefore, the effect of isoprenaline (ISO), activators and inhibitors of the protein kinase A (PKA) pathway on I(Kr) and I(Ks) was studied in canine ventricular myocytes using the whole cell patch clamp technique.


RESULTS
I (Kr) was significantly increased (by 30-50%) following superfusion with ISO, forskolin or intracellular application of PKA activator cAMP analogues (cAMP, 8-Br-cAMP, 6-Bnz-cAMP). Inhibition of PKA by Rp-8-Br-cAMP had no effect on baseline I(Kr). The stimulating effect of ISO on I(Kr) was completely inhibited by selective β₁-adrenoceptor antagonists (metoprolol and CGP-20712A), by the PKA inhibitor Rp-8-Br-cAMP and by the PKA activator cAMP analogues, but not by the EPAC activator 8-pCPT-2'-O-Me-cAMP. In comparison, I(Ks) was increased threefold by the activation of PKA (by ISO or 8-Br-cAMP), and strongly reduced by the PKA inhibitor Rp-8-Br-cAMP. The ISO-induced enhancement of I(Ks) was decreased by Rp-8-Br-cAMP and completely inhibited by 8-Br-cAMP.


CONCLUSIONS
The results indicate that the stimulation of β₁-adrenoceptors increases I(Kr), similar to I(Ks), via the activation of PKA in canine ventricular cells.
Department of Physiology, University of Debrecen, Debrecen, Hungary.
G
G
Harmati
T
T
Bányász
L
L
Bárándi
N
N
Szentandrássy
B
B
Horváth
G
G
Szabó
J A
JA
Szentmiklósi
G
G
Szénási
P P
PP
Nánási
J
J
Magyar
D000200:Action Potentials / Q000187:drug effects*; D058671:Adrenergic beta-1 Receptor Antagonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051668:Delayed Rectifier Potassium Channels / Q000378:metabolism*; D004285:Dogs; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008790:Metoprolol / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D059010:Single-Cell Analysis
D058671:Adrenergic beta-1 Receptor Antagonists; D000318:Adrenergic beta-Agonists; D051668:Delayed Rectifier Potassium Channels; D007093:Imidazoles; D047428:Protein Kinase Inhibitors; D018342:Receptors, Adrenergic, beta-1; C049763:CGP 20712A; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D008790:Metoprolol; D007545:Isoproterenol