Grichtchenko I I, Chesler M
Department of Physiology & Biophysics, N.Y.U. Medical Centre, NY 10016.
Neuroscience. 1994 Oct;62(4):1057-70. doi: 10.1016/0306-4522(94)90343-3.
Gliotic hippocampal slices were used to study glial acid secretion in a tissue largely devoid of neural elements. Rat hippocampal slices were prepared 10-28 days after sterotaxic injection of kainate. Cresyl Violet staining and immunohistochemistry for glial fibrillary acidic protein demonstrated a loss of neurons and a proliferation of reactive astrocytes in area CA3. Extracellular pH and K+ shifts were recorded in CA3 in response to K+ iontophoresis. Elevation of K+ evoked an extracellular acid shift that was two- to three-fold larger in gliotic versus unlesioned tissue. Ba2+ caused a slow extracellular acidification, and blocked both the depolarizing responses of the glial cells and the acid shifts evoked by K+. The K(+)-evoked acid shifts were abolished in Na(+)-free media, and diminished in HEPES-buffered solutions. Inhibition of extracellular carbonic anhydrase caused a reversible enhancement of the K(+)-evoked acid shifts, an effect that could be mimicked during H+ iontophoresis in agarose gels. Gliotic acid shifts were unaffected by amiloride or its analogs, stilbenes, zero Cl- media, zero or elevated glucose, lactate transport inhibitors, zero Ca2+ or Cd2+. Smaller acid shifts could be evoked in normal slices which were also enhanced by benzolamide, and blocked by Ba2+ and zero Na+ media. It is concluded that acid secretion by reactive astrocytes is Na+ and HCO3(-)-dependent and is triggered by depolarization. The similar pharmacological and ionic sensitivity of the acid shifts in non-gliotic tissue suggest that these properties are shared by normal astrocytes. These characteristics are consistent with the operation of an electrogenic Na(+)-HCO3- co-transporter. However, the enhancement of the acid shifts by inhibitors of extracellular carbonic anhydrase suggests that CO3(2-), rather than HCO3-, is the transported acid equivalent.
使用胶质化的海马切片来研究在一个基本上没有神经成分的组织中的胶质酸分泌。在立体定位注射海藻酸10 - 28天后制备大鼠海马切片。甲酚紫染色和胶质纤维酸性蛋白免疫组织化学显示CA3区神经元缺失和反应性星形胶质细胞增殖。记录CA3区细胞外pH值和K⁺变化以响应K⁺离子电泳。K⁺升高引起细胞外酸变化，胶质化组织中的这种变化比未损伤组织大两到三倍。Ba²⁺引起缓慢的细胞外酸化，并阻断胶质细胞的去极化反应以及K⁺引起的酸变化。在无Na⁺培养基中，K⁺引起的酸变化被消除，在HEPES缓冲溶液中则减小。抑制细胞外碳酸酐酶导致K⁺引起的酸变化可逆增强，这种效应在琼脂糖凝胶中进行H⁺离子电泳时可模拟。胶质化酸变化不受amiloride或其类似物、二苯乙烯、零Cl⁻培养基、零或升高的葡萄糖、乳酸转运抑制剂、零Ca²⁺或Cd²⁺影响。在正常切片中可诱发较小的酸变化，苯并酰胺也可增强这种变化，并被Ba²⁺和零Na⁺培养基阻断。结论是反应性星形胶质细胞的酸分泌依赖于Na⁺和HCO₃⁻，并由去极化触发。非胶质化组织中酸变化的相似药理学和离子敏感性表明正常星形胶质细胞也具有这些特性。这些特征与电中性Na⁺ - HCO₃⁻共转运体的运作一致。然而，细胞外碳酸酐酶抑制剂对酸变化的增强表明被转运的酸等价物是CO₃²⁻，而不是HCO₃⁻。
