TY - JOUR
T1 - K(Ca)3.1 channel downregulation and impaired endothelium-derived hyperpolarization-type relaxation in pulmonary arteries from chronically hypoxic rats
AU - Kroigaard, Christel
AU - Kudryavtseva, Olga
AU - Dalsgaard, Thomas
AU - Wandall-Frostholm, Christine
AU - Olesen, Søren-Peter
AU - Simonsen, Ulf
PY - 2013/4
Y1 - 2013/4
N2 - New Findings: • What is the central question of this study? Do the function and expression of small (KCa2) and intermediate (KCa3.1) conductance calcium-activated potassium channels increase as a compensatory mechanism to counteract hypoxia-induced pulmonary hypertension in rats? • What is the main finding and its importance? Our findings provide evidence for impaired endothelium-derived hyperpolarization-type relaxation in chronically hypoxic pulmonary small arteries despite upregulation of KCa2.3 channels. Our findings suggest that KCa3.1 channels are important for the maintenance of endothelium-derived hyperpolarization-type relaxation. Calcium-activated potassium channels of small (KCa2, SK) and intermediate (KCa3.1, IK) conductance are involved in endothelium-dependent relaxation of pulmonary arteries. We hypothesized that the function and expression of KCa2 and KCa3.1 increase as a compensatory mechanism to counteract hypoxia-induced pulmonary hypertension in rats. For functional studies, pulmonary arteries were mounted in microvascular myographs for isometric tension recordings. The KCa channel expression was evaluated by immunoblotting and quantitative PCR. Although ACh induced similar relaxations, the ACh-induced relaxations were abolished by the combined inhibition of nitric oxide synthase (by l-nitro-arginine, l-NOARG), cyclo-oxygenase (by indomethacin) and soluble guanylate cyclase (by ODQ) in pulmonary arteries from hypoxic rats, whereas 20 ± 6% (n= 8) maximal relaxation in response to ACh persisted in arteries from normoxic rats. Inhibiting Na+,K+-ATPase with ouabain or blocking KCa2 and KCa3.1 channels reduced the persisting ACh-induced relaxation. In the presence of l-NOARG and indomethacin, a novel KCa2 and KCa3.1 channel activator, NS4591, induced concentration- and endothelium-dependent relaxations, which were markedly reduced in arteries from chronically hypoxic rats compared with arteries from normoxic rats. The mRNA levels of KCa2.3 and KCa3.1 were unaltered, whereas KCa2.3 protein expression was upregulated and KCa3.1 protein expression downregulated in pulmonary arteries from rats exposed to hypoxia. In conclusion, endothelium-dependent relaxation was conserved in pulmonary arteries from chronically hypoxic rats, while endothelium-derived hyperpolarization (EDH)-type relaxation was impaired in chronically hypoxic pulmonary small arteries despite upregulation of KCa2.3 channels. Since impaired EDH-type relaxation was accompanied by KCa3.1 channel protein downregulation, these findings suggest that KCa3.1 channels are important for the maintenance of EDH-type relaxation.
AB - New Findings: • What is the central question of this study? Do the function and expression of small (KCa2) and intermediate (KCa3.1) conductance calcium-activated potassium channels increase as a compensatory mechanism to counteract hypoxia-induced pulmonary hypertension in rats? • What is the main finding and its importance? Our findings provide evidence for impaired endothelium-derived hyperpolarization-type relaxation in chronically hypoxic pulmonary small arteries despite upregulation of KCa2.3 channels. Our findings suggest that KCa3.1 channels are important for the maintenance of endothelium-derived hyperpolarization-type relaxation. Calcium-activated potassium channels of small (KCa2, SK) and intermediate (KCa3.1, IK) conductance are involved in endothelium-dependent relaxation of pulmonary arteries. We hypothesized that the function and expression of KCa2 and KCa3.1 increase as a compensatory mechanism to counteract hypoxia-induced pulmonary hypertension in rats. For functional studies, pulmonary arteries were mounted in microvascular myographs for isometric tension recordings. The KCa channel expression was evaluated by immunoblotting and quantitative PCR. Although ACh induced similar relaxations, the ACh-induced relaxations were abolished by the combined inhibition of nitric oxide synthase (by l-nitro-arginine, l-NOARG), cyclo-oxygenase (by indomethacin) and soluble guanylate cyclase (by ODQ) in pulmonary arteries from hypoxic rats, whereas 20 ± 6% (n= 8) maximal relaxation in response to ACh persisted in arteries from normoxic rats. Inhibiting Na+,K+-ATPase with ouabain or blocking KCa2 and KCa3.1 channels reduced the persisting ACh-induced relaxation. In the presence of l-NOARG and indomethacin, a novel KCa2 and KCa3.1 channel activator, NS4591, induced concentration- and endothelium-dependent relaxations, which were markedly reduced in arteries from chronically hypoxic rats compared with arteries from normoxic rats. The mRNA levels of KCa2.3 and KCa3.1 were unaltered, whereas KCa2.3 protein expression was upregulated and KCa3.1 protein expression downregulated in pulmonary arteries from rats exposed to hypoxia. In conclusion, endothelium-dependent relaxation was conserved in pulmonary arteries from chronically hypoxic rats, while endothelium-derived hyperpolarization (EDH)-type relaxation was impaired in chronically hypoxic pulmonary small arteries despite upregulation of KCa2.3 channels. Since impaired EDH-type relaxation was accompanied by KCa3.1 channel protein downregulation, these findings suggest that KCa3.1 channels are important for the maintenance of EDH-type relaxation.
KW - Animals
KW - Anoxia
KW - Chronic Disease
KW - Disease Models, Animal
KW - Down-Regulation
KW - Endothelium, Vascular
KW - Intermediate-Conductance Calcium-Activated Potassium Channels
KW - Male
KW - Muscle Relaxation
KW - Muscle, Smooth, Vascular
KW - Nitric Oxide Synthase
KW - Ouabain
KW - Potassium Channel Blockers
KW - Pulmonary Artery
KW - Rats
U2 - 10.1113/expphysiol.2012.066340
DO - 10.1113/expphysiol.2012.066340
M3 - Journal article
C2 - 23243147
SN - 0958-0670
VL - 98
SP - 957
EP - 969
JO - Experimental Physiology
JF - Experimental Physiology
IS - 4
ER -