Activation of protein kinase A partially reverses the effects of 2,3-butanedione monoxime on the transient outward K+ current of rat ventricular myocytes.
The transient outward K+ current (Ito) was assessed in single rat ventricular myocytes with the whole-cell patch-clamp technique. Extracellular application of the chemical phosphatase 2,3-butanedione monoxime (BDM) inhibited Ito in a concentration-dependent manner. The IC50 was 14 mM. The on-set of this effect occurred within 20 s after BDM application. Ito recovered almost completely at 2 min after washout of BDM. Application of 20 mM BDM shifted the steady-state inactivation curve of Ito by 9 +/- 2 mV (n = 8) in the negative direction. Addition of 5 microM isoproterenol enhanced Ito amplitude by 16.2 +/- 1.8%. This concentration of isoproterenol partially reversed the BDM-induced inhibition of Ito. Furthermore, application of 10 mM 8-bromoadenosine 3':5'-cyclic monophosphate enhanced the amplitude of Ito and also significantly reversed the BDM-induced suppression of Ito. In contrast, intracellular dialysis with guanosine 3':5'-cyclic monophosphate (cGMP, 1-10 mM) did not affect the BDM-induced inhibition of Ito. The inward rectifier K+ current (Ik1) was relatively insensitive to BDM; i.e., 20 mM BDM inhibited Ito and Ik1 to 35.5 +/- 4.3% (n = 8) and 92.9 +/- 4.0% (n = 4) of the control, respectively. These results indicate that BDM suppressed Ito but not Ik1 of rat ventricular myocytes. We attribute the BDM suppression of Ito to dephosphorylation of the channel protein.
Xiao
Y F
YF
Department of Pharmacology & Toxicology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark 07103-2714, USA.
McArdle
J J
JJ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D003931:Diacetyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D004789:Enzyme Activation; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D010766:Phosphorylation; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D011921:Rats, Inbred WKY
D015221:Potassium Channels; C004717:diacetylmonoxime; D017868:Cyclic AMP-Dependent Protein Kinases; D003931:Diacetyl; D007545:Isoproterenol; D002118:Calcium