Hernandez Z M, Morales M, Smith D S, del Castillo J
Comp Biochem Physiol A Comp Physiol. 1987;86(2):355-9. doi: 10.1016/0300-9629(87)90342-2.
In the presence of calcium, Ba2+ ions, at concentrations as low as 1-2 mM, block the action potentials (a.p.'s) elicited by the electrical stimulation of the primary spines of Diadema antillarum. Lower concentrations of barium (0.1 mM) potentiate the a.p.'s recorded from spines equilibrated with Ca-Free artificial sea water (ASW). Exposure of the spines to a saturated solution of EDTA in Ca-free, unbuffered ASW reversibly blocks their electrical activity. Spines blocked by EDTA continue to generate a.p.'s following their equilibration with Ca-free ASW containing 1 mM of Ba2+ ions. The time course of the a.p.'s recorded from spines equilibrated with normal ASW is only slightly affected by the combined action of 15 mM of tetraethylammonium (TEA) and 5 mM of 4-aminopyridine (4-AP). In contrast, the duration of the a.p.'s recorded from spines blocked by EDTA and placed in 1 mM barium is markedly increased by the combined actions of TEA and 4-AP at the above concentrations. We conclude that the Ca-channels of the neurites present in Diadema spines are not, at least qualitatively, an exception with regard to their permeation by Ba2+. The blocking action of low concentrations of these ions, particularly in the presence of calcium, may be explained by the extremely high surface to volume ratio prevailing in neurites with a diameter of only less than 0.1-0.3 micron.
在有钙存在的情况下，钡离子（Ba2+）浓度低至1 - 2 mM时，就能阻断由电刺激冠海胆（Diadema antillarum）初级棘突引发的动作电位（a.p.）。较低浓度的钡（0.1 mM）能增强在无钙人工海水（ASW）中平衡后的棘突所记录到的动作电位。将棘突暴露于无钙、无缓冲的ASW中的EDTA饱和溶液中，会可逆地阻断其电活动。被EDTA阻断的棘突在与含有1 mM Ba2+离子的无钙ASW平衡后，仍能继续产生动作电位。在正常ASW中平衡后的棘突所记录到的动作电位的时间进程，仅受到15 mM四乙铵（TEA）和5 mM 4 - 氨基吡啶（4 - AP）联合作用的轻微影响。相比之下，在上述浓度下，TEA和4 - AP的联合作用会显著延长被EDTA阻断并置于1 mM钡中的棘突所记录到的动作电位的持续时间。我们得出结论，冠海胆棘突中神经突的钙通道，至少在定性方面，在钡离子的通透方面并非例外。这些离子低浓度时的阻断作用，尤其是在有钙存在的情况下，可能是由于直径仅小于0.1 - 0.3微米的神经突中普遍存在的极高表面积与体积比所导致的。
