Regulation of vascular tension in diabetic coronary artery by large conductance Ca²⁺-activated K⁺ channel in rats

Objective: To investigate the regulation in vascular tension of diabetic coronary artery by large conductance Ca²⁺-activated K⁺ channel (BK channel) and to elucidate the mechanisms of coronary dysfunctions due to diabetes. Methods: Regulation of vascular tension in normal coronary artery was evaluated by videomicroscopy system. Streptozotocin-induced rat diabetic animal model was established successfully by intraperitoneal injection. Coronary smooth muscle cells were isolated by enzyme digestion. The BK currents in control and diabetic groups were recorded by patch clamp technique in whole cell configuration. Changes of vascular tension in normal and diabetic coronary arteries were assayed by multi-wire myograph system. Results: More than 50% was contracted in inner diameters of coronary arteries when 100 nmol/L IBTX, a specific BK channel blocker, was applied. In comparison with normal group, the BK current densities in diabetic group significantly decreased when test potentials were more than 60 mV (P < 0.05). The BK current densities at 150 mV in normal group and diabetic group were (275 ± 40) pA/pF and (70 ± 10) pA/pF respectively. When 100 mmol/L KC1 was washed out, vascular tensions of normal and diabetic coronary artery were (398 ± 38) mg and (390 ± 35) mg respectively (P > 0.05); however, when 100 nmol/L TBTX was added, the vascular tensions of normal and diabetic coronary artery were (395 ± 40) mg and (50 ± 7) mg (P < 0.05). Conclusion: BK channels play an important role in the regulation of coronary vascular tension, whereas BK channels in diabetic coronary artery are dysfunction, BK currents decrease and vascular tensions increase.