Mechanism of receptor-mediated modulation of the delayed outward potassium current in guinea-pig ventricular myocytes.
1. Receptor-mediated modulation of the delayed outward potassium current (IK) was investigated in guinea-pig single ventricular cells by using whole-cell voltage clamp and intracellular dialysis. 2. Isoprenaline increased IK in a dose-dependent manner with a half-maximum dose of 1.8 X 10(-8) M. Isoprenaline (10(-6) M) maximally increased IK by a factor of 2.85. This effect did not depend on the concentration of intracellular Ca2+ [( Ca2+]i). 3. External application of 10(-5) M-forskolin and internal application of 5 X 10(-5) M-cyclic AMP or 5 X 10(-6) M of the catalytic subunit of cyclic AMP-dependent protein kinase (PKA) also increased IK about 3-fold. The effect of isoprenaline on IK was masked by previous application of cyclic AMP. 4. All the above phosphorylating agents increased the amplitude of IK without a significant change in the current kinetics. 5. In the presence of 10(-5) M-forskolin, an additional application of 10(-8) M-12-O-tetradecanoylphorbol-13-acetate, an activator of protein kinase C (PKC), produced a further increase in IK, suggesting that the active sites of PKA and PKC on the IK channel are different. 6. Acetylcholine (10(-6) M) suppressed IK when the current was previously enhanced by 2 X 10(-8) M-isoprenaline, but had little effect in the absence of isoprenaline. 7. We conclude that beta-adrenergic modulation of IK is mediated by cyclic AMP-dependent phosphorylation but not by an increase in [Ca2+]i, that PKA and PKC enhance IK independently, and that acetylcholine antagonizes beta-adrenergic stimulation of IK most probably by inhibiting adenylate cyclase.
Yazawa
K
K
National Institute for Physiological Sciences, Okazaki, Japan.
Kameyama
M
M
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001665:Binding Sites; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011493:Protein Kinase C / Q000494:pharmacology; D016276:Ventricular Function
D010703:Phorbol Esters; D015221:Potassium Channels; D005576:Colforsin; D000242:Cyclic AMP; D011493:Protein Kinase C; D007545:Isoproterenol; D000109:Acetylcholine; D011188:Potassium