Inhibitory Effects of Blockage of Intermediate Conductance Ca^(2+) -Activated K^+ Channels on Proliferation of Hepatocellular Carcinoma Cells

The roles of intermediate conductance Ca2＋-activated K＋ channel （IKCal） in the pathogene- sis of hepatocellular carcinoma （HCC） were investigated. Immunohistochemistry and Western blotting were used to detect the expression of IKCal protein in 50 HCC and 20 para-carcinoma tissue samples. Real-time PCR was used to detect the transcription level of IKCal mRNA in 13 HCC and 11 para-carcinoma tissue samples. The MTT assay was used to measure the function of IKCal in human HCC cell line HepG2 in vitro. TRAM-34, a specific blocker of IKCal, was used to intervene with the function of IKCal. As compared with para-carcinoma tissue, an over-expression of IKCal protein was detected in HCC tissue samples （P〈0.05）. The mRNA expression level of IKCal in HCC tissues was 2.17 times higher than that in para-carcinoma tissues. The proliferation of HepG2 cells was suppressed by TRAM-34 （0.5, 1.0, 2.0 and 4.0 pxnol/L） in vitro （P〈0.05）. Our results suggested that IKCal may play a role in the proliferation of human HCC, and IKCal blockers may represent a potential therapeutic strategy for HCC.

Tacrolimus Inhibits Vasoconstriction by Increasing Ca^(2+) Sparks in Rat Aorta

The present study attempted to test a novel hypothesis that Ca^2＋ sparks play an important role in arterial relaxation induced by tacrolimus. Recorded with confocal laser scanning microscopy, tacrolimus（10 μmol/L） increased the frequency of Ca^2＋ sparks, which could be reversed by ryanodine（10 μmol/L）. Electrophysiological experiments revealed that tacrolimus（10 μmol/L） increased the large-conductance Ca^2＋-activated K＋ currents（BKCa） in rat aortic vascular smooth muscle cells（AVSMCs）, which could be blocked by ryanodine（10 μmol/L）. Furthermore, tacrolimus（10 and 50 μmol/L） reduced the contractile force induced by norepinephrine（NE） or KCl in aortic vascular smooth muscle in a concentration-dependent manner, which could be also significantly attenuated by iberiotoxin（100 nmol/L） and ryanodine（10 μmol/L） respectively. In conclusion, tacrolimus could indirectly activate BKCa currents by increasing Ca^2＋ sparks released from ryanodine receptors, which inhibited the NE- or KCl-induced contraction in rat aorta.

Molecular mechanisms of diabetic coronary dysfunction due to large conductance Ca2＋-activated K＋ channel impairment

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 Ca2＋-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 Ca2＋ iS impaired in diabetic rats. Moreover, cytoplasmic application of DHS-1 （a specific BK channel i~ 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 Ca2＋ and was significantly attenuated in the presence of high free calcium concentration, i.e., 1 μmol/L Ca2＋. Immunoblotting experiments confirmed that there was a 2-fold decrease in BK-β1 protein expression in diabetic vessels, without alterinq the BK channel a-subunit expression.Although the cytosolic Ca2＋ 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-β1 expression made these channels less sensitive to intracellular Ca2＋, 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-β1 expression and reduction of the β1-mediated BK channel activation in diabetic vessels.

Rotenone partially reversed the decreased BK_Ca currents in STZ-induced diabetic cerebral artery smooth muscle cells

Objective: Reactive oxygen species (ROS) causes the vascular complications and impairs vasodilation in diabetes mellitus. Big-conductance Ca2+-activated potassium channels (BKCa)