蝎毒素BmkTXKβ对家兔心房肌细胞瞬间外向钾电流的抑制作用

Inhibitory Effect of BmkTXKβ on Transient Outward Potassium Current in Rabbit Atrial Myocytes

为研究蝎毒素BmkTXKβ对家兔心房肌细胞瞬间外向钾电流 (Ito)的影响 ,采用全细胞膜片钳技术记录应用BmkTXKβ前后的Ito电流 .结果显示BmkTXKβ (1μmol/L)使心房肌细胞Ito (刺激电压为 +5 0mV)从(13 6 3± 0 87)pA/ pF减少到 (7 98± 0 78) pA/pF ,抑制率为 4 1 4 % (n =16 ,P <0 0 0 1) .冲洗后 ,Ito部分恢复至 (11 18± 0 82 ) pA/pF (n =6 ,P <0 0 1,与给药后比较 ) .在 0 0 1～ 10 0 μmol/L范围内BmkTXKβ呈浓度依赖性地抑制Ito,IC50 的均值为 0 95 μmol/L (n =10 ,P <0 0 1) ,但无频率依赖性 (n =6 ,P >0 0 5 ) .1μmol/L的BmkTXKβ可使Ito通道的失活动力学曲线明显左移 ,V1/ 2 分别为 (- 2 3 6± 2 7)mV和 (- 35 3± 3 6 )mV(n =8,P <0 0 5 ) ,曲线斜率基本不变 .同时可使Ito通道的恢复过程明显减慢 ,恢复曲线右移 ,τ值从 (5 1 2±8 5 )ms延长至 (93 5± 13 4 )ms (n =9,P <0 0 1) ,但不影响其激活过程 .据此推断BmkTXKβ对家兔心房肌细胞Ito具有显著的抑制作用 ,主要作用于失活过程 。

In order to study the effects of BmkTXKβ on transient outward potassium current( I to ) of isolated rabbit atrial myocytes,standard whole cell patch clamp technique was used to record I to before and after administration of extracellular BmkTXKβ with multiple concentrations. The results showed that: (1) At a dose of 1 μmol/L, it decreased I to by 41 4% ( n =16, P <0 001) at membrane potential of +50 mV [from (13 63±0 87) pA/pF to (7 98±0 78) pA/pF]. After washout, I to restored to (11 18±0 82) pA/pF ( n =6, P <0 01). (2) It significantly reduced I to in a clearly concentration dependent manner at the range of 0 01～100μmol/L with an IC 50 value of 0 95 μmol/L ( n =10, P <0 01), but without any change in frequency dependence ( n =6, P >0 05). (3) In the absence and presence of BmkTXKβ (1 μmol/L),the activation curves from relative conductance almost overlapped, whereas steady state inactivation curve shifted to left from (-23 6±2 7) mV to (-35 3±3 6) mV at V 1/2 point significantly ( n =8, P <0 05). The time for 50% recovery delayed obviously from(51 2±8 5) ms to (93 5±13 4) ms in the absence and presence of 1 μmol/L BmkTXKβ( n =9, P <0 01). The results show that BmkTXKβ exerts direct blocking effect on I to in rabbit atrial myocytes, which is mainly caused by a strong suppression effect on inactivation duration and prolongation of the recovery duration from inavtivation.