Wang Y X, Bezprozvannaya S, Bowersox S S, Nadasdi L, Miljanich G, Mezo G, Silva D, Tarczy-Hornoch K, Luther R R
Department of Pharmacology, Neurex Corporation, Menlo Park, CA 94025, USA.
Naunyn Schmiedebergs Arch Pharmacol. 1998 Feb;357(2):159-68. doi: 10.1007/pl00005150.
The ability of a series of synthetic analogues of omega-conopeptides MVIIA (SNX-111) and TVIA (SNX-185) to prevent electrically-evoked norepinephrine release from rat tail artery and hippocampal slice preparations was determined in an effort to identify voltage-sensitive calcium channel (VSCC) blockers that selectively target N-type VSCCs in central nervous system tissue. Electrical field stimulation (3 Hz, 1 ms in duration. 80 V for 1 min) caused a high and consistent tritium outflow from rat tail artery and hippocampal slice preparations preloaded with [3H]-norepinephrine. All conopeptides, chosen for their selective affinities for high-affinity SNX-111 binding sites (i.e., N-type VSCCs) over high-affinity omega-conopeptides MVIIC (SNX-230) binding sites (i.e., P/Q-type VSCCs), produced a concentration-dependent inhibition of calcium dependent electrically-evoked tritium outflow from both tail arteries and hippocampal slices: IC50s ranged from 1.2 nM to 1.2 microM. Blocking potencies (IC50s) in the tail artery assay were significantly correlated with those measured in the hippocampal slice preparation (r = 0.91, P = 0.00000012). There was a significant correlation between IC50s for blockade of hippocampal norepinephrine release and the inhibition of high-affinity [125I]-SNX-I11 binding in rat brain synaptosomes (r = 0.76, P = 0.00028). Blockade of hippocampal norepinephrine release was not significantly correlated with the inhibition of high-affinity SNX-230 binding (r = 0.46, P = 0.056). Maximum inhibition of tritium outflow in the tail artery assay was 22+/-1.4% of control, approximating the value (20.9+/-16.0% of control) obtained in the absence of extracellular Ca2+. In contrast, the maximum inhibition of tritium release from hippocampal slices was 36.8+/-2.5% of control (P < 0.05, compared to that of the tail artery assay). These results suggest that (1) N-type VSCCs alone mediate low frequency electrical stimulation-evoked neurotransmitter release from peripheral sympathetic efferents (tail artery) while both N-type and non-N type(s) mediate neurotransmitter release from CNS neurons (hippocampus); and (2) analogues of omega-conopeptides MVIIA and TVIA do not differentiate between N-type VSCCs mediating norepinephrine release from central and peripheral neural tissues.
测定了一系列ω-芋螺毒素MVIIA（SNX-111）和TVIA（SNX-185）的合成类似物阻止大鼠尾动脉和海马脑片标本中电诱发的去甲肾上腺素释放的能力，以鉴定在中枢神经系统组织中选择性靶向N型电压敏感钙通道（VSCC）的VSCC阻滞剂。电场刺激（3Hz，持续1ms，80V，持续1分钟）导致预先加载[3H]-去甲肾上腺素的大鼠尾动脉和海马脑片标本中有大量且一致的氚流出。所有芋螺毒素因其对高亲和力SNX-111结合位点（即N型VSCC）的选择性亲和力高于高亲和力ω-芋螺毒素MVIIC（SNX-230）结合位点（即P/Q型VSCC）而被选用，它们对尾动脉和海马脑片中钙依赖性电诱发的氚流出均产生浓度依赖性抑制：IC50范围为1.2nM至1.2μM。尾动脉试验中的阻断效力（IC50）与海马脑片标本中测得的阻断效力显著相关（r = 0.91，P = 0.00000012）。海马去甲肾上腺素释放阻断的IC50与大鼠脑突触体中高亲和力[125I]-SNX-I11结合的抑制之间存在显著相关性（r = 0.76，P = 0.00028）。海马去甲肾上腺素释放的阻断与高亲和力SNX-230结合的抑制没有显著相关性（r = 0.46，P = 0.056）。尾动脉试验中氚流出的最大抑制为对照的22±1.4%，接近在无细胞外Ca2+时获得的值（对照的20.9±16.0%）。相比之下，海马脑片氚释放量的最大抑制为对照的36.8±2.5%（与尾动脉试验相比，P < 0.05）。这些结果表明：（1）单独的N型VSCC介导外周交感神经传出纤维（尾动脉）低频电刺激诱发的神经递质释放，而N型和非N型VSCC均介导中枢神经系统神经元（海马）的神经递质释放；（2）ω-芋螺毒素MVIIA和TVIA的类似物不能区分介导中枢和外周神经组织中去甲肾上腺素释放的N型VSCC。
