title: Molecular mechanisms of diabetic coronary dysfunction due to large conductance Ca2⁺-activated K⁺ channel impairment.
abstract: BACKGROUND
  Diabetes mellitus is associated with coronary dysfunction, contributing to a 2- to 4-fold increase in the risk of coronary heart diseases. The mechanisms by which diabetes induces vasculopathy involve endothelial-dependent and -independent vascular dysfunction in both type 1 and type 2 diabetes mellitus. The purpose of this study is to determine the role of vascular large conductance Ca(2+)-activated K(+) (BK) channel activities in coronary dysfunction in streptozotocin-induced diabetic rats.
  
  
  METHODS
  Using videomicroscopy, immunoblotting, fluorescent assay and patch clamp techniques, we investigated the coronary BK channel activities and BK channel-mediated coronary vasoreactivity in streptozotocin-induced diabetic rats.
  
  
  RESULTS
  BK currents (defined as the iberiotoxin-sensitive K(+) component) contribute (65 ± 4)% of the total K(+) currents in freshly isolated coronary smooth muscle cells and > 50% of the contraction of the inner diameter of coronary arteries from normal rats. However, BK current density is remarkably reduced in coronary smooth muscle cells of streptozotocin-induced diabetic rats, leading to an increase in coronary artery tension. BK channel activity in response to free Ca(2+) is impaired in diabetic rats. Moreover, cytoplasmic application of DHS-1 (a specific BK channel b(1) subunit activator) robustly enhanced the open probability of BK channels in coronary smooth muscle cells of normal rats. In diabetic rats, the DHS-1 effect was diminished in the presence of 200 nmol/L Ca(2+) and was significantly attenuated in the presence of high free calcium concentration, i.e., 1 mmol/L Ca(2+). Immunoblotting experiments confirmed that there was a 2-fold decrease in BK-b(1) protein expression in diabetic vessels, without altering the BK channel α-subunit expression. Although the cytosolic Ca(2+) concentration of coronary arterial smooth muscle cells was increased from (103 ± 23) nmol/L (n = 5) of control rats to (193 ± 22) nmol/L (n = 6, P < 0.05) of STZ-induced diabetic rats, reduced BK-b(1) expression made these channels less sensitive to intracellular Ca(2+), which in turn led to enhanced smooth muscle contraction.
  
  
  CONCLUSIONS
  Our results indicated that BK channels are the key determinant of coronary arterial tone. Impaired BK channel function in diabetes mellitus is associated with down-regulation of BK-b(1) expression and reduction of the b(1)-mediated BK channel activation in diabetic vessels.
authors.affiliation: Department of Cardiology, Wuxi People's Hospital Affiliated to Nanjing Medical University, Wuxi, Jiangsu 214023, China. ruxingw@yahoo.com.cn
authors.forename: Ru-Xing
authors.initials: RX
authors.lastname: Wang
authors.forename: Hai-Feng
authors.initials: HF
authors.lastname: Shi
authors.forename: Qiang
authors.initials: Q
authors.lastname: Chai
authors.forename: Ying
authors.initials: Y
authors.lastname: Wu
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.forename: Yuan
authors.initials: Y
authors.lastname: Ji
authors.forename: Yong
authors.initials: Y
authors.lastname: Yao
authors.forename: Ku-Lin
authors.initials: KL
authors.lastname: Li
authors.forename: Chang-Ying
authors.initials: CY
authors.lastname: Zhang
authors.forename: Jie
authors.initials: J
authors.lastname: Zheng
authors.forename: Su-Xia
authors.initials: SX
authors.lastname: Guo
authors.forename: Xiao-Rong
authors.initials: XR
authors.lastname: Li
authors.forename: Tong
authors.initials: T
authors.lastname: Lu
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003331:Coronary Vessels / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism* / Q000503:physiopathology; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism / Q000503:physiopathology; D004594:Electrophysiology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels