非洲爪蟾卵母细胞GABA_B和GABA_C受体介导的电流反应

Current responses mediated by endogenous GABA_B and GABA_C receptors in Xenopus oocytes

实验应用双电极电压箝技术 ,在具有滤泡膜的非洲爪蟾 (Xenopuslaevis)卵母细胞上记录到γ 氨基丁酸(γ aminobutyricacid ,GABA) 激活电流。此GABA 激活电流的特点及有关GABA受体类型的研究和分析如下 :( 1)在 3 5 5 % ( 5 5 / 15 5 )的受检细胞外加GABA可引起一慢的浓度依赖性的外向电流。 ( 2 )GABAA 受体的选择性拮抗剂bicuculline ( 10 -5mol/L)对GABA ( 10 -5mol/L)引起的外向电流无阻断作用 (n =6)。 ( 3 )GABAB 受体的选择性拮抗剂2 hydroxysaclofen ( 10 -4mol/L)能将GABA ( 10 -5mol/L)引起的外向电流可逆性地转变为内向电流 ,后者又可被GABAC 受体的选择性拮抗剂I4AA ( 10 -5mol/L)所消除 (n =6)。 ( 4 )GABAB 受体的特异性激动剂baclofen可引起部分 ( 2 0 % ,12 / 60 )受检细胞产生一慢的浓度依赖性的外向电流。 3× 10 -6 、3× 10 -5及 3× 10 -4mol/L 2 hydroxysaclofen分别阻断baclofen ( 10 -5mol/L) 激活电流 ( 6 3± 3 2 ) % ,( 4 4 1± 2 2 ) %及 ( 86 0± 1 6) % (n =6)。 ( 5 )baclofen激活电流的I V曲线显示逆转电位在 - 96 8± 7 2mV左右 ,此电流可分别被TEA ( 5mmol/L)和BaCl2 ( 2mmol/L)所阻断。以上结果提示 :在非洲爪蟾的卵母细胞上存在内源性GABAB 和GABAC 受体 。

The properties of GABA activated current in Xenopus oocytes and its underlying mechanism were studied using the two electrode voltage clamp technique. External application of GABA (10 -10 ～10 -3 mol/L) induced a concentration dependent outward current in a proportion of oocytes (35 5%, 55/155). Selective GABA A receptor antagonist bicuculline (10 -5 mol/L) did not block the GABA activated current ( n =6). However, 2 hydroxysaclofen (10 -4 mol/L), a GABA B receptor antagonist, reversed the GABA activated outward current to an inward current ( n =9), which was abolished completely by application of I4AA (10 -5 mol/L), a GABA C receptor selective antagonist ( n =6). In 20% (12/60) of oocytes, application of baclofen (10 -10 ～10 -4 mol/L), a GABA B receptor agonist, also induced a concentration dependent outward current 2 Hydroxysaclofen at the concentrations of 3×10 -6 , 3×10 -5 and 3×10 -4 mol/L blocked the baclofen (10 -5 mol/L) activated outward current by (6 3±3 2)%, (44 1±2 2)%, and (86 0±1 6)%, respectively ( n =6). The reversal potential for baclofen activated current was around -96 8±7 2 mV ( n =6), and the baclofen activated current could be blocked by TEA ( n =5) and Ba 2+ ( n =5). These results suggest that there exist endogenous GABA receptors, GABA B receptors mediating a slow and sustained outward current and GABA C receptors mediating an inward current in follicular Xenopus oocytes.