Modulation of Kv1.5 currents by protein kinase A, tyrosine kinase, and protein tyrosine phosphatase requires an intact cytoskeleton.
The regulation of cardiac delayed rectifier potassium (Kv) currents by cAMP-dependent protein kinase (PKA) contributes to the control of blood pressure and heart rate. We investigated the modulation by PKA and protein phosphatases of cloned Kv1.5 channels expressed in Xenopus laevis oocytes. Exposure of oocytes to activators of PKA (100 nM forskolin, 1 mM 8-bromo-cAMP, or 1 mM 3-isobutyl-1-methylxanthine) had no effect on the amplitude of Kv1.5 currents. Inhibition of PKA by injection of protein kinase A inhibitor peptide or exposure to myristoylated protein kinase A inhibitor peptide (M-PKI; 100 nM) reduced currents mediated by Kv1.5. M-PKI also reduced the amplitude of currents mediated by mutated Kv1.5 channels in which the COOH terminal PKA phosphorylation sites and PSD-95, Disc-large, and ZO-1-binding domain were removed. The reduction of Kv1.5 currents by M-PKI was attenuated by inhibition of actin polymerization by 1 microM cytochalasins B and D, but was not affected by 10 microM phalloidin (stabilizes actin filaments) or 50 microM colchicine (disrupts microtubules). Treatment of oocytes with antisense oligonucleotides against alpha-actinin-2 abolished the reduction in Kv1.5 current by M-PKI. These observations suggest that Kv1.5 currents are activated by endogenous PKA in "resting" oocytes and that inhibition of PKA activity reveals the action of endogenous phosphatases. Indeed, injection of alkaline phosphatase reduced currents mediated by Kv1.5. Further preincubation of oocytes with 1 mM sodium orthovanadate (a protein tyrosine phosphatase inhibitor) abolished the reduction in Kv1.5 currents by M-PKI. We conclude that currents encoded by Kv1.5 are regulated by PKA and protein tyrosine phosphatase and that this regulation requires an intact actin cytoskeleton and alpha-actinin-2.
Mason
H S
HS
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557-0046, USA.
Latten
M J
MJ
Godoy
L D
LD
Horowitz
B
B
Kenyon
J L
JL
D000185:Actinin / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003599:Cytoskeleton / Q000201:enzymology* / Q000502:physiology; D004285:Dogs; D004594:Electrophysiology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051666:Kv1.5 Potassium Channel; D009865:Oocytes; D010455:Peptides / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D014982:Xenopus laevis
D004791:Enzyme Inhibitors; D051666:Kv1.5 Potassium Channel; D010455:Peptides; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D000185:Actinin; D011505:Protein-Tyrosine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D017027:Protein Tyrosine Phosphatases