Abstract:

BACKGROUND: Large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels play a critical role in regulating the cellular excitability and vascular tone. The reports about the mechanisms of the smooth muscle BK_Ca channels on the conduit arteries are rare.
OBJECTIVE: To investigate the effects of aerobic exercise on the rat thoracic aortic contractility, and to explore the possible BK_Ca channel mechanisms underlying these effects.
METHODS: Twenty male Wistar rats were randomly divided into sedentary group and aerobic exercise group. Rats in the aerobic exercise group were preformed with 12 week-treadmill exercise, 0° slope, 20 m/min, 60 min/d, 5 d/wk. After 12 weeks, some animals (n=5 in each group) underwent femoral arterial and venous cannulation. Following 1 day recovery, the cardiovascular responses were monitored in vivo without anesthesia. For the rest animals (n=5 in each group), the thoracic aorta was carefully dissected free, cut into rings, and the endothelial cell lining was removed. The vessel contractility was examined in vitro.
RESULTS AND CONCOUSION: ①The pressor responses induced by intravenous injection of norepinephrine were attenuated in the aerobic exercise group. ②Intravenous injection of iberiotoxin, a selective BK_Ca channel blocker, caused a pressor response, which was more prominent in aerobic exercise group. ③120 mmol/L KCl elicited a significantly increase of vascular tone in both groups, and there was no significant differences of the maximal tension between two groups. ④Norepinephrine (10^-9-10^-5 mol/L) induced a concentration-dependent contraction of thoracic aorta in both groups, while the maximal tension in exercise group was significant less than that in the sedentary group. ⑤Iberiotoxin (3×10^-8 mol/L) pretreatment could enhance the NE-induced tension increase, which was more significant in exercise training group. ⑥BKCa channel opener NS1619 (10^-10-10^-6 mol/L) could cause a decrease of norepinephrine-induced vascular contraction, and the sensitivity of tissue to NS619 (pD2) was higher in exercise group than that in the sedentary group. These results suggest that aerobic exercise can change the cardiovascular reactivity and vascular contractility, in which the smooth muscle BKCa channels play an important role.