introduction Endothelin-1 Inhibits Inward Rectifier K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells Through Protein Kinase C

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1 Current Topic 6 ก มภาพ นธ 2549 เวลา น. น าเสนอโดย น.ส.สายวร ณ ศร ร ง อาจารย ท ปร กษา อ.นพ.ล อชา บ ญทว ก ล Endothelin-1 Inhibits Inward Rectifier K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells Through Protein Kinase C Park, Won Sun*; Han, Jin*; Kim, Nari*; Youm, Jae Boum*; Joo, Hyun*; Kim, Hyung Kyu*; Ko, Jae-Hong ; Earm, Yung E 1 Journal cardiovascular pharmacology volume46, number5, November introduction small arteries play a major role in the control of systemic blood pressure & local blood flow respond to changes in luminal flow, intravascular pressure & local metabolites local metabolites vasodilation 3 K + is one of several factors that link increases in blood flow, membrane potential, and vascular tone during coronary and cerebral ischemia, extracellular K + concentrations > 10 mm extracellular K+ concentrations (~15 mm) in small coronary and cerebral arteries vasodilation 4 mechanisms explain K+-induced vasodilations including activation of Kir channels and Na + /K + ATPases The vasodilation of small arteries is blocked by extracellular Ba 2+ (<50 µm) Endothelin-1 (ET-1) is the most potent vasoconstrictor Previous studies of vessels of the systemic circulation revealed that ET-1 modulated various types of ion channels the effects of ET-1 on ion channels? 5 the effect of ET-1 on Kir channels in vascular smooth muscle cells has not been studied. 6

2 Cell Preparation New Zealand White rabbits (1.5 ~ 2.0 kg) sodium pentobarbitone (50 mg kg-1) + heparin (100 U kg-1) hearts were removed and immersed in normal Tyrode solution left anterior descending (LAD) coronary arteries and all branches connected to LAD were dissected 7 8 Cell Preparation Electrophysiology Rabbit Coronary Arterial Smooth Muscle Cell (video edge detector) - diameter <100 µm - diameter 100 ~ 200 µm - diameter >200 µm whole-cell & cell-attached configurations 9 10 Western Blot Ba 2+ -Sensitive Kir Currents in Rabbit Coronary Arterial Smooth Muscle Cells detect one protein in mixture 11 12

3 Whole-cell control Ba µm [Ba 2+ ]=50 μm voltage step from -60 to -140 mv 13 : Ba µm O : control 14 ramp-depolarizing pulse from -140 to 20 mv, 0.5 mv/s 15 The reversal potential = -1.8 ± Density of Kir currents Western blot analysis 1.6 ± 0.4 pa / pf 4.2 ± 0.6 pa / pf 11.2 ± 0.6 pa / pf (1) and (2) * P < 0.01 versus # P < 0.01 versus 17 Kir2.1 is expressed in smaller coronary artery smooth muscle cells 18

4 Whole-cell control ET-1 30 nm Effects of ET-1 on Kir Currents Ba µm [ET-1]=30nM 19 [Ba 2+ ]=50 μm voltage step from -60 to -140 mv 20 } 57.6 ± 3.8% } 57.6 ± 3.8% 36.6 ± 4.3% { : Ba µm O : control 36.6 ± 4.3% { : ET nM 22 ramp-depolarizing pulse dose-response curve K d : 17.4 ± 5.9 nm K d : 73.6 ± 5.3 nm from -140 to 20 mv, 0.5 mv/s 23 24

5 cell-attached patches for single-channel recordings from a cell-attached patch control Ba µm ET-1 30 nm close open [Ba 2+ ]=50 μm [ET-1]=30nM close open close open holding potential corresponded to -140 mv the current-voltage relationship for unitary currents *P < 0.01 versus control #P < versus ET-1 ET-1 (30 nm) significantly reduced the Kir channel activity Whole-cell Effect of ET A and ET B Antagonists on ET-1-Mediated Inhibition of Kir Currents - ET-1 30 nm - BQ-123 (3 µm) (ET A receptor blockade) - ET-1 30 nm - BQ-788 (3 µm) (ETB receptor blockade) 29 30

6 : Ba µm O : control : ET nM 32 Whole-cell Protein Kinase C Mediates Inhibitory Effects of ET-1 on Kir Channels Staurosporine (100 nm) GF X (GFX) (1 μm) effect of staurosporine on the ET-1- induced inhibition of Kir currents 8.2 ± 1.2% 6.1 ± 1.9% 35 staurosporine 8.2 ± 1.2% 6.1 ± 1.9% (GFX) 9.2 ± 1.7 % 4.4 ± 1.1% 36

7 Whole-cell effect of PDBu on the ET-1-induced inhibition of Kir currents PDBu (1 µm) OAG (1 µm) 64.6 ± 5.2% 39.0 ± 3.5% Activity of K ATP, BK Ca, and K V Channels in and PDBu 64.6 ± 5.2% 39.0 ± 3.5% OAG 60.5 ± 4.4 % 31.8 ± 2.5% activate the K ATP channels in and activate the K ATP channels in and [pinacidil]=10 µm [glibenclamide ]=10 µm 41 42

8 activate the K ATP channels in and inward current is the K ATP current 11.1 ± ± dose-dependent inhibition of K ATP currents activate the BK Ca channels in and intracellular & extracellular free Ca 2+ concentration was maintained at 300 nm iberiotoxin (IbTX) (a potent inhibitor of BK Ca ) voltage ramp from -80 to +80 mv for 320 milliseconds activate the BK Ca channels in and effect of IbTx on the activity of the BK ca channel : IbTX O : control 47 48

9 effect of 5 nm ET-1 on the activity of the BK Ca channel Voltage-dependent K+ currents Voltage-dependent K+ currents holding potential is -60 mv pulse potentials between -120 and +60 mv IbTX reduce BK Ca ET-1= 30 nm

10 This findings of this study Kir current density of small-diameter coronary arteries > Kir current density of larger arteries ET-1 Kir current in & the ET-1-induced inhibition of the Kir channel mediated by activation of the ET A receptor This findings of this study effect of ET-1 on the Kir current was attenuated by the inhibition of PKC and was mimicked by PKC activation K ATP, BK Ca, and K V currents and the effects of ET-1 on these channels did not differ between & 57 The Kir channels(kir2) identified in coronary & cerebral artery smooth muscle cells : - strong inward rectification - conductance dependent on the extracellular K + concentration - voltage - and time-dependent gating process - consensus sites for phosphorylation by protein kinases A and C 58 several reports have identified transcripts for Kir2.1 in smooth muscle cells of the coronary artery, but not transcripts for the other members of the Kir2 subfamily 59 Kir2.1 gene dilate in response to the extracellular K + eg. hypoxia and ischemia Kir2.1 plays an essential role in the regulation of vascular tone under conditions of metabolic stress 60

11 In this study they first detected only one Kir2.1 protein in freshly isolated, but not in, by Western blotting ET-1 inhibited Kir channels in cultured bovine pulmonary arterial endothelial cells Zhang et al the K ATP channels in porcine coronary artery are inhibited by ET-1 Miyoshi et al In this report : when smooth muscle cells were pretreated with PKC inhibitors (GF X and staurosporine) effect of ET-1 on K ATP channels other vasoconstrictors (eg, angiotensin II, phenylephrine, serotonin, histamine, and neuropeptide Y) have been shown to reduce KATP currents via the activation of PKC the best candidate for the mechanism of the inhibition of Kir channels by ET-1 might be related to PKC-mediated pathways in this study : the inhibitory effect of ET-1 on Kir currents is mediated by a PKC signal transduction pathway via activation of the ET A receptor many previous reports : K ATP and BK Ca channels are important for regulating basal tone in coronary, mesenteric, cerebral, and saphenous arteries In pulmonary arteries, K ATP and K V channels regulate the resting membrane potential 65 66

12 Previous reports : large arteries express several types of channels, However, the distribution of K ATP, BK Ca, and K V channels relative to vascular size has not been investigated previously the variations in responses that are related to differences in the arterial diameter might be a result of the differential expression of Kir channels In pulmonary arterial smooth muscle cell < 5 nm ET-1 BK Ca current (by increasing intracellular Ca 2+ concentration) their recent paper : ET-1 the K ATP channels by activation of Ca 2+ -independent PKC subtype ([varepsilon] subtype) in coronary and pulmonary arterial smooth muscle cells >10 nm ET-1 BK Ca current ET-1 has a effect on BK Ca channels directly and/or by activation of PKC 69 ET-1 the K V channel These effects of ET-1 were attenuated by inhibition of PLC and PKC. Shimoda et al 70 In this article: ET-1 Kir channels by activation of PKC Thus, these inhibitions of K+ (BK Ca, K ATP, K V, and Kir) channels by ET-1 may cause membrane depolarization the open Kir channels in middle cerebral artery maintained the resting diameter 8% - 12% more dilated than if these channels were closed or not present Johnson et al 71 72

13 RMP of coronary and cerebral artery smooth muscle cells was between -40 and -50 mv, which is positive relative to the reversal potential of K+ channels Therefore the physiological role for Kir channels requires outward currents through the channels Outward currents through the Kir channels have a physiological role in regulating the membrane potential and thus vascular tone 73 Kir channels that are open during the resting condition maintain coronary vessels in hyperpolarized state & dilated state the Kir channels contribute to the membrane potential and resting tone in the coronary arteries 74 the Kir channels are closed (eg.et-1) membrane depolarization voltage-dependent Ca 2+ entry vasoconstriction 75 76