Activation of BK_Ca channels via cyclic AMP‐ and cyclic GMP‐dependent protein kinases by eugenosedin‐A in rat basilar artery myocytes

Abstract

Background and purpose: The study investigated whether eugenosedin-A, a 5-hydroxytryptamine and a/b adrenoceptor antagonist, enhanced delayed-rectifier potassium (K DR )-or large-conductance Ca 2 þ -activated potassium (BK Ca )-channel activity in basilar artery myocytes through cyclic AMP/GMP-dependent and -independent protein kinases. Experimental approach: 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 þ -and Ca 2 þ -channel activities. Key results: Eugenosedin-A (1 mM) 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 mM) or iberiotoxin (IbTX, 0.1 mM), but not affected by a small-conductance K Ca blocker (apamin, 100 mM). BK Ca current activation by eugenosedin-A was significantly inhibited by an adenylate cyclase inhibitor (SQ 22536, 10 mM), a soluble guanylate cyclase inhibitor (ODQ, 10 mM), competitive antagonists of cAMP and cGMP (Rp-cAMP, 100 mM and Rp-cGMP, 100 mM), and cAMPand cGMP-dependent protein kinase inhibitors (KT5720, 0.3 mM and KT5823, 0.3 mM). Eugenosedin-A reversed the inhibition of BK Ca current induced by the protein kinase C activator, phorbol myristyl acetate (PMA, 0.1 mM). 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 þ current (I Ca,L ), but without modifying the voltage-dependence of the current. Conclusions and implications: Eugenosedin-A enhanced BK Ca currents by stimulating the activity of cyclic nucleotidedependent protein kinases. Physiologically, this activation would result in the closure of voltage-dependent calcium channels and thereby relax cerebral SMCs.

The Guanylyl Cyclase Activator YC-1 Directly Inhibits the Voltage-Dependent K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells

“…Several previous reports have suggested that the activation of the sGC-mediated increase in cGMP plays an important role in vasodilation by activation of BK Ca channels (42,43). Therefore, application of YC-1 could increase the K + efflux by activating BK Ca channels, although this conflicts with the observation that YC-1 induces Kv-channel inhibition.…”

“…However, in our experimental conditions, the activation of BK Ca channels were minimized by the inclusion of 10 mM BAPTA, a Ca 2+ chelator, in the pipette solution and the pretreatment with iberiotoxin (100 nM), a specific BK Ca -channel inhibitor, in the bath solution. Also, it has been reported that agonist-mediated activation of BK Ca channels through cAMP and cGMP-dependent protein kinases could be inhibited with treatment of 100 nM iberiotoxin (43). Therefore, we are confident that under our experimental conditions, there is a minimal contribution of BK Ca to the Kv currents.…”

Cyclic nucleotide-dependent relaxation pathways in vascular smooth muscle

“…3), respectively, based on the use of selective inhibitors of these kinases and/or direct application of biochemically purified kinase to the cytoplasmic face of excised, inside-out membrane patches containing BK Ca [60,[120][121][122][123][124][125][126]. For example, BK Ca activation by cAMP/PKA was observed in murine renal artery [127] and rat pulmonary artery [128].…”

Oestrogen upregulates the sarcoplasmic reticulum Ca2+ATPase pump in coronary arteries

“…In the present study we did not assess the potential effect of KT5823 alone on SERCA2b expression; instead, we determined the inhibitory effect of KT5823 against the E2‐mediated increase in SERCA2b expression. However, previous reports have suggested that KT5823 alone has similar effects as the control when evaluating the cGMP/PKG pathway in arterial endothelial and smooth muscle cells …”