Mechanism of activation of the Ca(2+)-activated K+ channel by cyclic AMP in cultured porcine coronary artery smooth muscle cells.
Activation of the Ca(2+)-activated K+ channel (KCa-channel) by adenosine 3', 5'-cyclic monophosphate (cAMP) and cAMP-dependent protein kinase (A-kinase) in cultured smooth muscle cells from porcine coronary artery was investigated using the patch-clamp technique. In cell-attached patches, the KCa-channel was activated when forskolin (10 microM) was applied to the bath. In excised inside-out patches, application of 50 microM cAMP to the bath activated the KCa-channel in the presence of A-kinase (10 units/ml) and ATP (1 mM). In addition, the KCa-channel was activated directly by application of cAMP to the cytoplasmic side of the membrane in the absence of A-kinase. The activation by cAMP or by A-kinase required intracellular Ca2+, and was enhanced by increase of intracellular Ca2+. At a low concentration (3 x 10(-7) M) of Ca2+, more than 2 mM cAMP was required for activation of the KCa-channel, but with 10(-6) M Ca2+, 100 microM cAMP was sufficient for activation. These results suggest that there are two mechanisms of activation of the KCa-channel by cAMP: direct activation, and indirect activation via phosphorylation of the channel by A-kinase.
Minami
K
K
Faculty of Pharmaceutical Sciences, Tokushima University, Japan.
Fukuzawa
K
K
Nakaya
Y
Y
Zeng
X R
XR
Inoue
I
I
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D003331:Coronary Vessels; D000242:Cyclic AMP / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011494:Protein Kinases / Q000502:physiology; D013552:Swine
D015221:Potassium Channels; D005576:Colforsin; D000242:Cyclic AMP; D011494:Protein Kinases; D002118:Calcium