Heemskerk F M, Schrama L H, Ghijsen W E, De Graan P N, Lopes da Silva F H, Gispen W H
Division of Molecular Neurobiology, Rudolf Magnus Institute, University of Utrecht, The Netherlands.
J Neurochem. 1991 Jun;56(6):1827-35. doi: 10.1111/j.1471-4159.1991.tb03437.x.
Recently we have shown that 4-aminopyridine (4-AP), a drug known to enhance transmitter release, stimulates the phosphorylation of the protein kinase C substrate B-50 (GAP-43) in rat brain synaptosomes and that this effect is dependent on the presence of extracellular Ca2+. Hence, we were interested in the relationship between changes induced by 4-AP in the intracellular free Ca2+ concentration ([Ca2+]i) and B-50 phosphorylation in synaptosomes. 4-AP (100 microM) elevates the [Ca2+]i (as determined with fura-2) to approximately the same extent as depolarization with 30 mM K+ (from an initial resting level of 240 nM to approximately 480 nM after treatment). However, the underlying mechanisms appear to be different: In the presence of 4-AP, depolarization with K+ still evoked an increase in [Ca2+]i, which was additive to the elevation caused by 4-AP. Several Ca2+ channel antagonists (CdCl2, LaCl3, and diphenylhydantoin) inhibited the increase in B-50 phosphorylation by 4-AP. It is interesting that the increase in [Ca2+]i and the increase in B-50 phosphorylation by 4-AP were attenuated by tetrodotoxin, a finding pointing to a possible involvement of Na+ channels in this action. These results suggest that 4-AP (indirectly) stimulates both Ca2+ influx and B-50 phosphorylation through voltage-dependent channels by a mechanism dependent on Na+ channel activity.
最近我们发现，4-氨基吡啶（4-AP）这种已知能增强递质释放的药物，可刺激大鼠脑突触体中蛋白激酶C底物B-50（GAP-43）的磷酸化，且这种作用依赖于细胞外Ca2+的存在。因此，我们对4-AP诱导的细胞内游离Ca2+浓度（[Ca2+]i）变化与突触体中B-50磷酸化之间的关系感兴趣。4-AP（100微摩尔）使[Ca2+]i升高（用fura-2测定）的程度与用30毫摩尔K+去极化时大致相同（从初始静息水平240纳摩尔升至处理后的约480纳摩尔）。然而，其潜在机制似乎不同：在存在4-AP的情况下，用K+去极化仍会引起[Ca2+]i升高，这是对4-AP所致升高的叠加。几种Ca2+通道拮抗剂（CdCl2、LaCl3和苯妥英）抑制了4-AP引起的B-50磷酸化增加。有趣的是，4-AP引起的[Ca2+]i升高和B-50磷酸化增加被河豚毒素减弱，这一发现表明Na+通道可能参与了这一作用。这些结果表明，4-AP（间接）通过依赖于Na+通道活性的机制，经电压依赖性通道刺激Ca2+内流和B-50磷酸化。
