Potentiation of slow component of delayed rectifier K(+) current by cGMP via two distinct mechanisms: inhibition of phosphodiesterase 3 and activation of protein kinase G.
1. Regulation of the slowly activating component of delayed rectifier K(+) current (I(Ks)) by intracellular guanosine 3'5' cyclic monophosphate (cGMP) was investigated in guinea-pig sino-atrial (SA) node cells using the whole-cell patch-clamp method. 2. When a cell was dialyzed with pipette solution containing 100 micro M cGMP, I(Ks) started to gradually increase and reached a maximum increase of a factor of 2.37 +/- 0.39 (n = 4) about 10-15 min after rupture of patch membrane. Atrial natriuretic peptide (ANP, 100 nM) also potentiated I(Ks), consistent with intracellular cGMP-induced enhancement of I(Ks). 3. Bath application of a selective blocker of the cGMP-inhibited phosphodiesterase (PDE3) milrinone (100 microM) enhanced I(Ks) by a factor of 1.50 +/- 0.09 (n = 4) but failed to further enhance I(Ks) after a maximum stimulation by intracellular cGMP (100 microM), suggesting that blockade of PDE3 activity is involved in the enhancement of I(Ks). A potent but nonspecific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX, 100 microM) further increased I(Ks) stimulated by 100 microM milrinone, indicating that PDE subtypes other than PDE3 are also involved in the regulation of basal I(Ks) in guinea-pig SA node cells. 4. Bath application of 100 microM 8-bromoguanosine 3'5' cyclic monophosphate (8-Br-cGMP) increased I(Ks) by a factor of 1.48 +/- 0.11 (n = 5) and this stimulatory effect was totally abolished by cGMP-dependent protein kinase (PKG) inhibitor KT-5823 (500 nM), suggesting that the activation of PKG also mediates cGMP-induced potentiation of I(Ks). 5. These results strongly suggest that intracellular cGMP potentiates I(Ks) not only by blocking PDE3 but also by activating PKG in guinea-pig SA node cells.
Department of Internal Medicine, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
Kentaro
K
Shimizu
Yutaka
Y
Shintani
Wei-Guang
WG
Ding
Hiroshi
H
Matsuura
Tadao
T
Bamba
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology / Q000502:physiology; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000502:physiology*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D051668:Delayed Rectifier Potassium Channels; D004789:Enzyme Activation; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D012849:Sinoatrial Node / Q000166:cytology / Q000378:metabolism
D051668:Delayed Rectifier Potassium Channels; D010726:Phosphodiesterase Inhibitors; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C016276:8-bromocyclic GMP; D009320:Atrial Natriuretic Factor; D017869:Cyclic GMP-Dependent Protein Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D006152:Cyclic GMP; D015056:1-Methyl-3-isobutylxanthine