Mechanism of receptor-mediated modulation of the delayed outward potassium current in guinea-pig ventricular myocytes

J Physiol. 1990 Feb;421:135-50. doi: 10.1113/jphysiol.1990.sp017937.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / pharmacology
  • Action Potentials / drug effects
  • Animals
  • Binding Sites
  • Colforsin / pharmacology
  • Cyclic AMP / pharmacology
  • Dose-Response Relationship, Drug
  • Guinea Pigs
  • Heart / physiology*
  • In Vitro Techniques
  • Isoproterenol / pharmacology
  • Phorbol Esters / pharmacology
  • Potassium / physiology*
  • Potassium Channels / physiology*
  • Protein Kinase C / pharmacology
  • Ventricular Function


  • Phorbol Esters
  • Potassium Channels
  • Colforsin
  • Cyclic AMP
  • Protein Kinase C
  • Isoproterenol
  • Acetylcholine
  • Potassium