| Objective: The purpose of this study is to investigate the effect of ISL on large-conductance Ca-activated K(2+ +BKCa) channel in the cerebral basilar arterial smooth muscle cells(VSMC) of spontaneous hypertensive rat. Methods: The change of SHR systolic pressure was measured by tail artery pressure measurement instrument before and after ISL intervention, after perfusion with 10-5 mol/L phenylephrine(PE), 10-5 mol/L PE+10-4 mol/L ISL and 10-5 mol/L PE, the diameter of the cerebral basilar artery in SHR was measured by pressure myograph, the currents of BKCa channel of single vascular smooth muscle cell(VSMC) was recorded by whole-cell patch-clamp technique and the c GMP levels of basilar artery was evaluated by ELISA. Results:(1) After intervention with ISL for 14 days, ISL decreased systolic pressure of SHR from 218.3±1.6 mm Hg to 119.2±1.9 mm Hg(p<0.01), there was no difference of systolic pressure between ISL-treated SHR and Wistar-Kyoto(WKY) rat.(2) 10-4 mol/L ISL relaxed the cerebral basilar artery(p<0.01). The isolated cerebral basilar artery was incubated with PE(10-5 mol/L) for 20 min, and the diameter was(235.6±26) μm, after perfusion with PE(10-5 mol/L) and ISL(10-4 mol/L), the diameter was(309.2±25) μm, after washing with PE( 10-5 mol/L) for 20 min, the diameter was(241.1±27) μm. The result suggested that ISL relaxed cerebral basilar artery of SHR.(3)Single VSMC was hold at-40 m V, the outward currents had not obviously enhanced in –40~-20 m V, but ISL enhanced the outward currents in a voltage-dependent manner in 0~ +60m V(n = 6, p< 0.05).(4) 10-7, 10-6, 10-5, 10-4 and 3×10-4mol/L ISL increased the outward current from(144±25) p A to(156±24) p A,(173±24) p A,(211±21) p A,(252±21) p A and(262±20) p A respectively. The result indicated that ISL enhanced outward currents in a concentration-dependent manner, EC50 of ISL enhanced the VSMC outward current was 9.5 μmol/L(n = 6, p< 0.05).(5) After intervention with ISL, the outward currents of VSMC increased from(212.1±32) p A to(283.2±28) p A(p<0.01, n=6), In the presence of 10-3 mol/L TEA(BKCa channel inhibitor) for 3 min, the enhanced current was reduced to(143.4±21) p A(n = 6, p<0.05). The result indicated ISL enhanced the outward currents mediated by BKCa channel.(6) In the presence of 10-5 mol/L MB(s GC inhibitor) for 3 min, the enhanced current induced by ISL in VSMC was reduced from(324.3±74) p A to(171.9±42) p A(p<0.05, n=6), compared with the control group(163.9±43) p A, there was no difference. The result indicated ISL enhanced the outward currents mediated by s GC.(7) BAPTA-AM a selective Ca2+ chelator, inhibited the basic outward currents in VSMC. In the absence of BAPTA-AM, ISL increased the outward currents of VSMC from(191.1±31) p A to(381±35) p A(n=6, p<0.01). In the presence of 20 μmol/L BAPTA-AM, ISL increased the outward currents of VSMC from(76.7±18) p A to(151.4±19) p A(n=6, p<0.01). The result indicated BAPTA-AM had no effect on the rate of ISL- enhancement outward current in VSMC.(8) After intervention with ISL for 14 days, ISL also increased the c GMP levels of basilar artery in SHR from(31.4±3.8) to(78.7±12.7) pmol/mg protein(p<0.05, n=6), compared with the WKY group(66±7.4) pmol/mg protein, there was no difference. The result indicated ISL increased the c GMP levels of basilar artery in SHR.Conclusion: Role of the ISL relaxing the cerebral basilar artery may be related to its effect in enhancing BKCa current by increasing the levels of c GMP in the VSMC, and lead to smooth muscle cells hyperpolarization, cerebral basilar artery relaxing and spontaneously hypertensive rats blood pressure reducing. |
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