Type 2 diabetes: increased expression and contribution of IK_Ca 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.

Crosstalk between cardiomyocyte-rich perivascular tissue and coronary arteries is reduced in the Zucker Diabetic Fatty rat model of type 2 diabetes mellitus

“…, Schach et al . ). Our observation that endothelial dysfunction is present in coronary arteries from ZDF rats, and persists in the presence of PVT, supports that changes in endothelial function can contribute to cardiovascular complications – such as ischaemic heart disease and ventricular dysfunction – commonly observed in type 2 diabetes.…”

Type 2 Diabetes Alters Intracellular Ca2+ Handling in Native Endothelium of Excised Rat Aorta

“…For instance, acetylcholine-induced vasodilation was preserved in coronary arteries despite reduced NO bioavailability because of IK Ca and SK Ca up-regulation [70]. Likewise, IK Ca was up-regulated and compensated for lower NO release OZDF mesenteric arteries stimulated with acetylcholine [71]. As discussed elsewhere [72], endothelial hyperpolarization enhances the driving force for agonist-induced extracellular Ca 2+ entry in vascular endothelium.…”

Calcium and electrical signaling in arterial endothelial tubes: New insights into cellular physiology and cardiovascular function

“…75,[125][126][127][128] In comparison with findings for actions of NO, how aging and conditions of high risk during old age (eg diabetes, hypertension) impact EDH through SK Ca /IK Ca channel activation is less clear. Some studies indicate a loss of endothelial SK Ca /IK Ca -dependent vasodilation, [129][130][131][132][133] whereas others have found an enhancement in SK Ca /IK Ca channel function of intact vessels 128,[134][135][136][137][138][139] and isolated endothelial tubes. 71 This discrepancy in conclusions can be attributed to differences in spe- The presence of SMCs presents activity of high conductance BK Ca channels which may mask analysis of the more modest conductance of SK Ca /IK Ca channels in ECs.…”