Activation of BKCa channels via cyclic AMP- and cyclic GMP-dependent protein kinases by eugenosedin-A in rat basilar artery myocytes.
OBJECTIVE
The study investigated whether eugenosedin-A, a 5-hydroxytryptamine and alpha/beta adrenoceptor antagonist, enhanced delayed-rectifier potassium (K(DR))- or large-conductance Ca(2+)-activated potassium (BK(Ca))-channel activity in basilar artery myocytes through cyclic AMP/GMP-dependent and -independent protein kinases.


METHODS
Cerebral smooth muscle cells (SMCs) were enzymatically dissociated from rat basilar arteries. Conventional whole cell, perforated and inside-out patch-clamp electrophysiology was used to monitor K(+)- and Ca(2+)-channel activities.


RESULTS
Eugenosedin-A (1 microM) did not affect the K(DR) current but dramatically augmented BK(Ca) channel activity in a concentration-dependent manner. Increased BK(Ca) current was abolished by charybdotoxin (ChTX, 0.1 microM) or iberiotoxin (IbTX, 0.1 microM), but not affected by a small-conductance K(Ca) blocker (apamin, 100 microM). BK(Ca) current activation by eugenosedin-A was significantly inhibited by an adenylate cyclase inhibitor (SQ 22536, 10 microM), a soluble guanylate cyclase inhibitor (ODQ, 10 microM), competitive antagonists of cAMP and cGMP (Rp-cAMP, 100 microM and Rp-cGMP, 100 microM), and cAMP- and cGMP-dependent protein kinase inhibitors (KT5720, 0.3 microM and KT5823, 0.3 microM). Eugenosedin-A reversed the inhibition of BK(Ca) current induced by the protein kinase C activator, phorbol myristyl acetate (PMA, 0.1 microM). Eugenosedin-A also prevented BK(Ca) current inhibition induced by adding PMA, KT5720 and KT5823. Moreover, eugenosedin-A reduced the amplitude of voltage-dependent L-type Ca(2+) current (I(Ca,L)), but without modifying the voltage-dependence of the current.


CONCLUSIONS
Eugenosedin-A enhanced BK(Ca) currents by stimulating the activity of cyclic nucleotide-dependent protein kinases. Physiologically, this activation would result in the closure of voltage-dependent calcium channels and thereby relax cerebral SMCs.
Wu
B-N
BN
Department and Graduate Institute of Pharmacology, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
Chen
C-F
CF
Hong
Y-R
YR
Howng
S-L
SL
Lin
Y-L
YL
Chen
I-J
IJ
D018674:Adrenergic Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001488:Basilar Artery / Q000166:cytology / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects* / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000187:drug effects* / Q000378:metabolism; D051668:Delayed Rectifier Potassium Channels / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005260:Female; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010879:Piperazines / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012702:Serotonin Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D015398:Signal Transduction
D018674:Adrenergic Antagonists; D051668:Delayed Rectifier Potassium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010879:Piperazines; D012702:Serotonin Antagonists; C496985:eugenosedin-A; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases
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