Soliven B, Szuchet S, Arnason B G, Nelson D J
Department of Neurology, University of Chicago, Illinois 60637.
J Membr Biol. 1988 Oct;105(2):177-86. doi: 10.1007/BF02009170.
Cultured ovine oligodendrocytes (OLGs) express a number of voltage-dependent potassium currents after they attach to a substratum and as they begin to develop processes. At 24-48 hours following plating, an outward potassium current can be identified that represents a composite response of a rapidly inactivating component and a steady-state or noninactivating component. After 4-7 days in culture, OLGs also develop an inward rectifier current. We studied the effects of forskolin and phorbol 12-myristate 13-acetate (PMA) on OLG outward currents. These compounds are known to alter the myelinogenic metabolism of OLGs. PMA, an activator of protein kinase C (PK-C), has been shown to enhance myelin basic protein phosphorylation while forskolin acting on adenylate cyclase, and thereby increasing cAMP, inhibits it. Both forskolin and PMA increase the phosphorylation of 2'3'-cyclic nucleotide phosphodiesterase, an OLG/myelin protein. We found that forskolin decreased the steady-state outward current at 120 mV by 10% at 100 nM, and by 72% at 25 microM from a holding potential of -80 mV. The time course of inactivation of the peak currents was decreased, affecting both the fast and slow time constants. There was no significant change in the steady-state parameters of current activation and inactivation. The effect of forskolin was attenuated when the adenylate cyclase inhibitor adenosine (2 mM) was present in the intracellular/pipette filling solution. The results of PMA experiments were similar to those obtained with forskolin. Whereas the amplitude of the currents in the presence of PMA was reduced by 28% at 1.5 nM and 60% and 600 nM, the decay phase of the peak currents was less affected. The PMA effect could still be seen when the intracellular Ca2+ was reduced to less than or equal to 10 nM with 5 mM BAPTA, but was inhibited when the cells were pre-exposed to 50 microM psychosine, a PK-C inhibitor. It is postulated that the potassium currents in OLG can be physiologically modulated by two distinct second-messenger systems, perhaps converging at the level of a common phosphorylated enzyme or regulatory protein.
培养的绵羊少突胶质细胞（OLGs）在附着于基质并开始形成突起后，会表达多种电压依赖性钾电流。在接种后的24 - 48小时，可识别出一种外向钾电流，它代表快速失活成分和稳态或非失活成分的复合反应。培养4 - 7天后，OLGs还会产生内向整流电流。我们研究了福斯高林和佛波酯12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）对OLG外向电流的影响。已知这些化合物会改变OLGs的髓鞘形成代谢。PMA是蛋白激酶C（PK - C）的激活剂，已被证明可增强髓鞘碱性蛋白的磷酸化，而作用于腺苷酸环化酶从而增加cAMP的福斯高林则会抑制这种磷酸化。福斯高林和PMA都会增加2',3'-环核苷酸磷酸二酯酶（一种OLG/髓鞘蛋白）的磷酸化。我们发现，从 - 80 mV的钳制电位开始，100 nM的福斯高林使120 mV处的稳态外向电流降低了10%，25 μM时降低了72%。峰值电流的失活时间进程缩短，对快速和慢速时间常数均有影响。电流激活和失活的稳态参数没有显著变化。当细胞内/移液管填充溶液中存在腺苷酸环化酶抑制剂腺苷（2 mM）时，福斯高林的作用减弱。PMA实验的结果与福斯高林的相似。在1.5 nM的PMA存在下，电流幅度降低了28%，在1.5 nM和600 nM时分别降低了60%，而峰值电流的衰减阶段受影响较小。当用5 mM BAPTA将细胞内Ca2+降低至小于或等于10 nM时，仍能看到PMA的作用，但当细胞预先暴露于50 μM鞘氨醇（一种PK - C抑制剂）时，PMA的作用受到抑制。据推测，OLG中的钾电流可能受到两种不同的第二信使系统的生理调节，这两种系统可能在一种共同的磷酸化酶或调节蛋白水平上汇聚。
