Korean J Physiol Pharmacol.  2024 Sep;28(5):469-478. 10.4196/kjpp.2024.28.5.469.

Effect of aortic smooth muscle BK channels on mediating chronic intermittent hypoxia-induced vascular dysfunction

• Zhang P
• Zou P
• Huang X
• Zeng X
• Liu S
• Liu Y
• Shao L

• KMID: 2559139
• DOI: http://doi.org/10.4196/kjpp.2024.28.5.469

Abstract

Chronic intermittent hypoxia (CIH) can lead to vascular dysfunction and increase the risk of cardiovascular diseases, cerebrovascular diseases, and arterial diseases. Nevertheless, mechanisms underlying CIH-induced vascular dysfunction remain unclear. Herein, this study analyzed the role of aortic smooth muscle calciumactivated potassium (BK) channels in CIH-induced vascular dysfunction. CIH models were established in rats and rat aortic smooth muscle cells (RASMCs). Hemodynamic parameters such as mean blood pressure (MBP), diastolic blood pressure (DBP), and systolic blood pressure (SBP) were measured in rats, along with an assessment of vascular tone. NO and ET-1 levels were detected in rat serum, and the levels of ET-1, NO, eNOS, p-eNOS, oxidative stress markers (ROS and MDA), and inflammatory factors (IL-6 and TNF-α) were tested in aortic tissues. The Ca²⁺ concentration in RASMCs was investigated. The activity of BK channels (BKα and BKβ) was evaluated in aortic tissues and RASMCs. SBP, DBP, and MBP were elevated in CIH-treated rats, along with endothelial dysfunction, cellular edema and partial detachment of endothelial cells. BK channel activity was decreased in CIH-treated rats and RASMCs. BK channel activation increased eNOS, p-eNOS, and NO levels while lowering ET-1, ROS, MDA, IL-6, and TNF-α levels in CIH-treated rats. Ca²⁺ concentration increased in RASMCs following CIH modeling, which was reversed by BK channel activation. BK channel inhibitor (Iberiotoxin) exacerbated CIH-induced vascular disorders and endothelial dysfunction. BK channel activation promoted vasorelaxation while suppressing vascular endothelial dysfunction, inflammation, and oxidative stress, thereby indirectly improving CIH-induced vascular dysfunction.

Keyword

Ca²⁺ concentration; Chronic intermittent hypoxia; Endothelin-1; Large-conductance calcium-activated potassium channels; Nitric oxide; Vascular dysfunction

Figure

• 

  Fig. 1 Vascular dysfunction occurs, and BK channel activity is repressed in chronic intermittent hypoxia (CIH)-treated rats. (A) Systolic blood pressure (SBP) in the normoxia and CIH groups. (B) Diastolic blood pressure (DBP). (C) Mean blood pressure (MBP). (D) Vascular tone assessment. (E) H&E staining to detect pathological changes in rat aorta. (F) Immunohistochemistry to measure the expression of BK channels in rat aortic tissues. N = 6. The data were expressed as mean ± standard deviation. Data comparison between two groups was performed with the unpaired student’s t-test, and data comparison among multiple groups was conducted with a one-way analysis of variance, with Tukey’s for post-hoc test. IOD, integrated optical density; PE, phenylephrine; ACh, acetylcholine; SNP, sodium nitroprusside. *p < 0.05 compared with the normoxia group.

• 

  Fig. 2 BK channel activation upregulates eNOS, raising NO expression in CIH-treated rats. (A) NO levels in rat aortic tissues. (B) NO levels in rat serum. (C) eNOS protein expression in rat aortic tissues examined with Western blotting. (D) p-eNOS expression in rat aortic tissues tested with Western blotting. N = 6. The data were presented as mean ± standard deviation. Data comparison between two groups was performed with the unpaired student’s t-test, and data comparison among multiple groups was conducted with a one-way analysis of variance, with Tukey’s for post-hoc test. NO, nitric oxide; CIH, chronic intermittent hypoxia; eNOS, endothelial nitric oxide synthase; p-eNOS, phosphorylation-eNOS; DMSO, dimethyl sulfoxide. *p < 0.05 compared with the DMSO group.

• 

  Fig. 3 BK channel activation downregulates ET-1 and mitigates vascular endothelial dysfunction in CIH-treated rats. (A) Detection of ET-1 levels in rat serum. (B) Western blotting analysis of ET-1 protein expression in rat aortic tissues. (C) Vascular tone assessment. N = 6. The data were presented as mean ± standard deviation. Data between two groups was compared using the unpaired student’s t-test, and data comparison among multiple groups was conducted with a one-way analysis of variance, with Tukey’s for post-hoc test. ET-1, endothelin-1; CIH, chronic intermittent hypoxia; DMSO, dimethyl sulfoxide, PE, phenylephrine; ACh, acetylcholine; SNP, sodium nitroprusside. *p < 0.05 compared to the DMSO group.

• 

  Fig. 4 BK channel activation curbs vascular inflammation and oxidative stress in CIH-treated rats. (A) ROS levels. (B) MDA levels. (C) IL-6 levels. (D) TNF-α levels. (E) H&E staining results. Scale bar = 50 μm. N = 6. Data were expressed as mean ± standard deviation. Data comparison between two groups was performed with the unpaired student’s t-test, and data comparison among multiple groups was conducted with a one-way analysis of variance, with Tukey’s for post-hoc test. CIH, chronic intermittent hypoxia; ROS, reactive oxygen species; MDA, malondialdehyde; IL-6, interleukin-6; TNF-α, tumor necrosis factor alpha; DMSO, dimethyl sulfoxide. *p < 0.05 compared to the DMSO group.

• 

  Fig. 5 BK channel activation increases Bk α and Bkβ subunits, indirectly inhibiting vascular dysfunction. (A, B) Measurement of intracellular Ca2+ concentration. (B) Immunofluorescence observation of fluorescence intensity of Bkα (red) and Bkβ (green) proteins. Scale bar = 50 μm. The data were expressed as mean ± standard deviation. Data comparison between two groups was performed with the unpaired student’s t-test, and data comparison among multiple groups was conducted with a one-way analysis of variance, with Tukey’s for post-hoc test. CIH, chronic intermittent hypoxia; DMSO, dimethyl sulfoxide. *p < 0.05 compared with the control group, #p < 0.05 compared with the DMSO + CIH group.

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