The Effect Of Emodin On BK_Ca Channel Of Basilar Artery Smooth Muscle Cells In Spontaneously Hypertensive Rat

Objective:The purpose of this study is to investigate the effect of emodin on BKCa channel in BASMCs of SHR.Methods:Isolated cerebral basilar artery was used for vascular reactivity measurement with pressure myograph system. Tail artery pressure measurement instrument was used to measure the change of SHR systolic blood pressure before and after emodin intervention. Single vascular SMC was used for electrophysiological measurement with whole-cell patch-clamp recording technique. Immunohistochemistry and western blotting were used to study the distribution and expression of the BKCa channel β1subunit.Results:(1) After emodin intervention, SHR systolic pressures were reduced from223±16mmHg to127±12mmHg, and there was no difference between Wistar group and emodin intervention group.(2)After acute separated vascular segment was incubated in waterbath contained PE(10-5μmol/L) for20minutes, vascular segment diameter were increased from246.6±14.9μm to293.3±21.7μm with3×10-5mol/L emodin(n=6, p<0.05).(3) Single SMC was hold at-40mV, outward currents enhanced by voltage-dependent manner in20-60mV (n=6,p<0.05); with10-7,10-6or10-5mol/L emodin, outward currents enhanced by voltage-dependent manner.(4) TEA (10-3mol/L) and IBTX (10-7mol/L) both inhibited the emodin-induced outward currents (n=6, p<0.05).(5) When BASMCs were incubated in Ca2+free solution for30min, emodin (10-5mol/L)-induced BKca currents were disappeared (n=6, p>0.05).(6) Nimodipine and BAPTA-AM both inhibited the emodin-induced BKca channel currents (n=6, p>0.05).(7) Immunohistochemistry of BKCa channels showed that β1subunit distribution density was increased after emodin intervention (p<0.01, n=4/group).(8)Western blotting of BASMCs proteins showed the ratio of β1subunits expression was significant up-regulation in BASMCs in wistar group, SHR group and emodin intervention group, respectively (n=6, p<0.05).Conculsion:On one hand, Emodin relaxed cerebral basilar artery by enhancement BKCa currents via increasing Ca2+flow into intracellular, on the other hand, emodin increased β1subunits expression on BASMCs. More Pi subunits expression raised sensitivity to Ca2+which enhanced BKca-medicated outward currents, and lead to smooth muscle cells hyperpolarization, cerebral basilar artery relaxing and SHR blood pressure reducing.