title: Type 2 diabetes: increased expression and contribution of IKCa channels to vasodilation in small mesenteric arteries of ZDF rats.
abstract: Impaired endothelial function, which is dysregulated in diabetes, also precedes hypertension. We hypothesized that in Type 2 diabetes, the impaired endothelium-dependent relaxation is due to a loss of endothelium-derived hyperpolarization (EDH) that is regulated by impaired ion channel function. Zucker diabetic fatty (ZDF), Zucker heterozygote, and homozygote lean control rats were used as the experimental models in our study. Third-order mesenteric arteries were dissected and mounted on a pressure myograph; mRNA was quantified by RT-PCR and channel proteins by Western blotting. Under nitric oxide (NO) synthase and cyclooxygenase inhibition, endothelial stimulation with ACh fully relaxes control but not diabetic arteries. In contrast, when small-conductance calcium-activated potassium (KCa) channels and intermediate- and large-conductance KCa (I/BKCa) are inhibited with apamin and charybdotoxin, NO is able to compensate for ACh-induced relaxation in control but not in diabetic vessels. After replacement of charybdotoxin with 1-[(2-chlorophenyl)diphenylmethyl]-(1)H-pyrazole (TRAM-34; IKCa inhibitor), ACh-induced relaxation in diabetic animals is attenuated. Specific inhibition with TRAM-34 or charybdotoxin attenuates ACh relaxation in diabetes. Stimulation with 1-ethyl-2-benzimidazolinone (IKCa activator) shows a reduced relaxation in diabetes. Activation of BKCa with 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-(2)H-benzimidazol-2-one NS619 leads to similar relaxations of control and diabetic arteries. RT-PCR and Western blot analysis demonstrate elevated mRNA and protein expression levels of IKCa in diabetes. Our results suggest that the compensatory effect of NO and EDH-associated, endothelium-dependent relaxation is reduced in ZDF rats. Specific blockade of IKCa with TRAM-34 reduces NO and EDH-type relaxation in diabetic rats, indicating an elevated contribution of IKCa in diabetic small mesenteric artery relaxation. This finding correlates with increased IKCa mRNA and protein expression in this vessel.
authors.affiliation: Department of Cardiology, University Hospital Regensburg, Regensburg, Germany christian.schach@ukr.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Schach
authors.affiliation: Department of Cardiology, University Hospital Regensburg, Regensburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Resch
authors.affiliation: Department of Cardiology, University Hospital Regensburg, Regensburg, Germany.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Schmid
authors.affiliation: Department of Cardiology, University Hospital Regensburg, Regensburg, Germany.
authors.forename: Guenter A
authors.initials: GA
authors.lastname: Riegger
authors.affiliation: Department of Cardiology, University Hospital Regensburg, Regensburg, Germany.
authors.forename: Dierk H
authors.initials: DH
authors.lastname: Endemann
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001562:Benzimidazoles / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D006579:Heterozygote; D006720:Homozygote; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D008638:Mesenteric Arteries / Q000378:metabolism* / Q000502:physiology; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011924:Rats, Zucker; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014664:Vasodilation
chemical_list: D001562:Benzimidazoles; D002120:Calcium Channel Agonists; D016861:Cyclooxygenase Inhibitors; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D011720:Pyrazoles; D012333:RNA, Messenger; D051640:Small-Conductance Calcium-Activated Potassium Channels; C411671:TRAM 34; D018999:Charybdotoxin; C086491:NS 1619; D001030:Apamin; D052250:Nitric Oxide Synthase Type III; C102635:1-ethyl-2-benzimidazolinone; D000109:Acetylcholine
keywords: calcium-activated potassium channel; diabetes; endothelium; endothelium-derived hyperpolarization; mesenteric artery; nitric oxide; vasodilation