Regional heterogeneity in acetylcholine-induced relaxation in rat vascular bed

Role of calcium-activated K+ channels

Rob H P Hilgers, Joseph Todd, R Clinton Webb

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Abstract

Ca+-activated K+-channels (KCa) regulate vasomotor tone via smooth muscle hyperpolarization and relaxation. The relative contribution of the endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation differs depending on vessel type and size. It is unknown whether these KCa channels are differentially distributed along the same vascular bed and hence have different roles in mediating the EDHF response. We therefore assessed the role of small- (SKCa), intermediate- (IK Ca), and large-conductance (BKCa) channels in mediating acetylcholine-induced relaxations in both first- and fourth-order side branches of the rat superior mesenteric artery (MA1 and MA4, respectively). Two-millimeter segments of each MA were mounted in the wire myograph, incubated with Nω-nitro-L-arginine methyl ester (L-NAME, 100 μmol/l) and indomethacin (10 μmol/l), and precontracted with phenylephrine (10 μmol/l). Cumulative concentration-response curves to ACh (0.001-10 μmol/l) were performed in the absence or presence of selective KCa channel antagonists. Apamin almost completely abolished these relaxations in MA4 but only partially blocked relaxations in MA1. The selective IKCa channel blocker 1-[(2chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) caused a significantly greater inhibition of the ACh-induced relaxation in MA4 compared with MA1. Iberiotoxin had no inhibitory effect in MA4 but blunted relaxation in MA1. Relative mRNA expression levels of SKCa (rSK1, rSK3, and rSK4 = rIK1) were significantly higher in MA4 compared with MA1. BKCa (rBKα1 and rBKβ1) genes were similar in both MA1 and MA4. Our data demonstrate regional heterogeneity in SKCa and IKCa function and gene expression and stress the importance of these channels in smaller resistance-sized arteries, where the role of EDHF is more pronounced.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume291
Issue number1
DOIs
StatePublished - Jul 12 2006

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Calcium-Activated Potassium Channels
NG-Nitroarginine Methyl Ester
Indomethacin
Acetylcholine
Endothelium
Blood Vessels
Apamin
Muscle Relaxation
Superior Mesenteric Artery
Phenylephrine
Smooth Muscle
Arteries
Gene Expression
Messenger RNA
Genes

ASJC Scopus subject areas

  • Physiology

Cite this

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title = "Regional heterogeneity in acetylcholine-induced relaxation in rat vascular bed: Role of calcium-activated K+ channels",
abstract = "Ca+-activated K+-channels (KCa) regulate vasomotor tone via smooth muscle hyperpolarization and relaxation. The relative contribution of the endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation differs depending on vessel type and size. It is unknown whether these KCa channels are differentially distributed along the same vascular bed and hence have different roles in mediating the EDHF response. We therefore assessed the role of small- (SKCa), intermediate- (IK Ca), and large-conductance (BKCa) channels in mediating acetylcholine-induced relaxations in both first- and fourth-order side branches of the rat superior mesenteric artery (MA1 and MA4, respectively). Two-millimeter segments of each MA were mounted in the wire myograph, incubated with Nω-nitro-L-arginine methyl ester (L-NAME, 100 μmol/l) and indomethacin (10 μmol/l), and precontracted with phenylephrine (10 μmol/l). Cumulative concentration-response curves to ACh (0.001-10 μmol/l) were performed in the absence or presence of selective KCa channel antagonists. Apamin almost completely abolished these relaxations in MA4 but only partially blocked relaxations in MA1. The selective IKCa channel blocker 1-[(2chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) caused a significantly greater inhibition of the ACh-induced relaxation in MA4 compared with MA1. Iberiotoxin had no inhibitory effect in MA4 but blunted relaxation in MA1. Relative mRNA expression levels of SKCa (rSK1, rSK3, and rSK4 = rIK1) were significantly higher in MA4 compared with MA1. BKCa (rBKα1 and rBKβ1) genes were similar in both MA1 and MA4. Our data demonstrate regional heterogeneity in SKCa and IKCa function and gene expression and stress the importance of these channels in smaller resistance-sized arteries, where the role of EDHF is more pronounced.",
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T2 - Role of calcium-activated K+ channels

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AU - Todd, Joseph

AU - Webb, R Clinton

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N2 - Ca+-activated K+-channels (KCa) regulate vasomotor tone via smooth muscle hyperpolarization and relaxation. The relative contribution of the endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation differs depending on vessel type and size. It is unknown whether these KCa channels are differentially distributed along the same vascular bed and hence have different roles in mediating the EDHF response. We therefore assessed the role of small- (SKCa), intermediate- (IK Ca), and large-conductance (BKCa) channels in mediating acetylcholine-induced relaxations in both first- and fourth-order side branches of the rat superior mesenteric artery (MA1 and MA4, respectively). Two-millimeter segments of each MA were mounted in the wire myograph, incubated with Nω-nitro-L-arginine methyl ester (L-NAME, 100 μmol/l) and indomethacin (10 μmol/l), and precontracted with phenylephrine (10 μmol/l). Cumulative concentration-response curves to ACh (0.001-10 μmol/l) were performed in the absence or presence of selective KCa channel antagonists. Apamin almost completely abolished these relaxations in MA4 but only partially blocked relaxations in MA1. The selective IKCa channel blocker 1-[(2chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) caused a significantly greater inhibition of the ACh-induced relaxation in MA4 compared with MA1. Iberiotoxin had no inhibitory effect in MA4 but blunted relaxation in MA1. Relative mRNA expression levels of SKCa (rSK1, rSK3, and rSK4 = rIK1) were significantly higher in MA4 compared with MA1. BKCa (rBKα1 and rBKβ1) genes were similar in both MA1 and MA4. Our data demonstrate regional heterogeneity in SKCa and IKCa function and gene expression and stress the importance of these channels in smaller resistance-sized arteries, where the role of EDHF is more pronounced.

AB - Ca+-activated K+-channels (KCa) regulate vasomotor tone via smooth muscle hyperpolarization and relaxation. The relative contribution of the endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation differs depending on vessel type and size. It is unknown whether these KCa channels are differentially distributed along the same vascular bed and hence have different roles in mediating the EDHF response. We therefore assessed the role of small- (SKCa), intermediate- (IK Ca), and large-conductance (BKCa) channels in mediating acetylcholine-induced relaxations in both first- and fourth-order side branches of the rat superior mesenteric artery (MA1 and MA4, respectively). Two-millimeter segments of each MA were mounted in the wire myograph, incubated with Nω-nitro-L-arginine methyl ester (L-NAME, 100 μmol/l) and indomethacin (10 μmol/l), and precontracted with phenylephrine (10 μmol/l). Cumulative concentration-response curves to ACh (0.001-10 μmol/l) were performed in the absence or presence of selective KCa channel antagonists. Apamin almost completely abolished these relaxations in MA4 but only partially blocked relaxations in MA1. The selective IKCa channel blocker 1-[(2chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) caused a significantly greater inhibition of the ACh-induced relaxation in MA4 compared with MA1. Iberiotoxin had no inhibitory effect in MA4 but blunted relaxation in MA1. Relative mRNA expression levels of SKCa (rSK1, rSK3, and rSK4 = rIK1) were significantly higher in MA4 compared with MA1. BKCa (rBKα1 and rBKβ1) genes were similar in both MA1 and MA4. Our data demonstrate regional heterogeneity in SKCa and IKCa function and gene expression and stress the importance of these channels in smaller resistance-sized arteries, where the role of EDHF is more pronounced.

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