The Effect Of Aerobic Exercise On The Biophysical Properties Of BKca Channels In Rat Cerebral Artery Smooth Muscle Cells

Introduction:To investigate the effect of aerobic exercise training on the biophysical properties of BKCa channels in rat cerebral artery smooth muscle cells.Methods:Thirty8-week-old male Wistar rats were randomly assigned into three groups (each n=10):sedentary control group (SED), low-frequency exersice-trained group (EX-3d/w) and high-frequency exersice-trained group (EX-5d/w). Exercise training was performed on a motor treadmill (0°slope,20m/min,50-55%VO2max,60min/day) at low frequency (3days/week, EX-3d/w) or high frequency (5days/week, EX-5d/w). Afer12weeks, the rats were anesthetized with urethane, the head was excised, and the brain was taken. The cerebral arteries were removed and cleaned of fat and connective tissue. By using enzymatic isolation method, a number of isolated cerebral arterial smooth muscle cells were obtained for electrophysiological study. Single channel biophysical properties were examined by using inside-out patch clamp recording technique.Results:(1) The identification of BKCa channels. According to the current (I)-voltage (V) curve, the conductance of the BKCa channel was210.5+10.3pS (R2=0.996, n=8). No rectification was observed and the reversal potensial was approximate to OmV. All the above indicate that the recording curves were elicited by BKCa channels.(2) Exersice significantly increased the activity of BKCa channels in VSMCs. There is a higher open probability (Po) of BKCa channels in exersice trained group at+40mV with1μ M [Ca2+] i (P<0.05). The Po of BKCa channels in EX-5d/w.group was higher than that of EX-3d/w group (P<0.05).(3) Aerobic exercise significantly increased the voltage dependence of BKCa channels. The (Normalized NPo)-V was left shifted by exersice, the V1/2value in SED group, EX-3d/w group and EX-5d/w group was44.52mV,37.08mV,26.55mV, respectively. The effect on EX-5d/w group was greater than that in EX-3d/w group.(4) Aerobic exercise induced an increase in the calcium dependence of the BKCa channels. The (Normalized NPo)-Log[Ca2+]i curves were left shifted by exercise. The Kd value in SED group, EX-3d/w group and EX-5d/w group was2.801μ M,1.39μ M, and0.35μ M, respectively. Morever, BKCa channels obtained from EX-5d/w group were more sensitive to Ca2+than those of EX-3d/w group (P<0.05).(5) Aerobic exercise training significantly increased the channel mean open time (To) and decreased the channel mean closed time (Tc).Conclusion:Regularly aerobic exercise may alter the biophysical properties of BKCa channels in rat cerebral arteries and increase the channel activity, which may be the mechanisms underlying the vascular dilation and blood flow maintenance in brain by aerobic exercise, and such beneficial effect may be volume-dependent.