Dourado M M, Brumwell C, Wisgirda M E, Jacob M H, Dryer S E
Department of Biological Science, Florida State University, Tallahassee, 32306-4075.
J Neurosci. 1994 May;14(5 Pt 2):3156-65. doi: 10.1523/JNEUROSCI.14-05-03156.1994.
The expression of appropriate ensembles of ionic channels is necessary for the differentiation and normal function of vertebrate neurons. Cell-cell interactions may regulate the expression and properties of ionic channels in embryonic neurons. Previous studies have shown that the expression of A-type K+ channels (IA) and Ca2+-activated K+ channels (lK[Ca]) is abnormal in chick ciliary ganglion neurons developing in vitro in the absence of normal cell-cell interactions. Other voltage-activated currents develop normally under these conditions. The present studies were designed to establish the role of the target tissues and the preganglionic innervation in regulating the expression of these currents in embryonic chick ciliary ganglion neurons developing in situ. Surgical manipulations were used to remove the developing optic vesicle, which contains the target tissues, the mid-dorsal region of the midbrain primordium, which contains the preganglionic nucleus, or both, all prior to the formation of the ciliary ganglion. IA and IK[Ca] were then examined in acutely isolated neurons that developed in ovo in the presence (OV+) or absence (OV-) of the normal target tissues, in the presence (MB+) or absence (MB-) of preganglionic innervation, and in the absence of both preganglionic innervation and target tissues (OV-/MB-). The amplitude of IA was unaffected by the operations. However, the activation and inactivation kinetics of IA were two- to threefold faster in OV- or OV-/MB- cells compared to neurons isolated from control OV+ ganglia at embryonic days 11-14 (E11-E14). There were no changes in the voltage dependence of activation or steady-state inactivation, or in the time course of recovery from inactivation. By contrast, neurons isolated from MB- ganglia expressed an IA with amplitude, voltage dependence, and kinetics that were indistinguishable from those of control MB+ and OV+ ganglia. Therefore, interactions with target tissues in the eye play a role in determining the characteristics of IA in developing ciliary ganglion neurons, whereas preganglionic innervation does not. Furthermore, the amplitude of IK[Ca] was reduced by 90-100% in OV-, MB-, and OV-/MB- neurons isolated at E12-E14 as compared to MB+ and OV+ controls. Voltage-activated Ca2+ currents were present at normal amplitudes in all of these neurons. Thus, the expression of IK[Ca] in chick ciliary ganglion neurons is regulated by both target tissue interactions and preganglionic innervation. Therefore, cell-cell interactions are necessary for the expression of a normal ensemble of ionic channels in chick ciliary ganglion neurons developing in situ.
离子通道适当组合的表达对于脊椎动物神经元的分化和正常功能是必需的。细胞间相互作用可能调节胚胎神经元中离子通道的表达和特性。先前的研究表明，在体外发育且缺乏正常细胞间相互作用的鸡睫状神经节神经元中，A型钾通道（IA）和钙激活钾通道（lK[Ca]）的表达异常。在这些条件下，其他电压激活电流正常发育。本研究旨在确定靶组织和节前神经支配在调节原位发育的胚胎鸡睫状神经节神经元中这些电流表达方面的作用。在睫状神经节形成之前，通过手术操作去除包含靶组织的发育中的视泡、包含节前神经核的中脑原基的中背区域或两者。然后在急性分离的神经元中检测IA和IK[Ca]，这些神经元在有（OV+）或无（OV-）正常靶组织、有（MB+）或无（MB-）节前神经支配以及无节前神经支配和靶组织（OV-/MB-）的情况下在卵内发育。IA的幅度不受手术影响。然而，与在胚胎第11 - 14天（E11 - E14）从对照OV+神经节分离的神经元相比，OV-或OV-/MB-细胞中IA的激活和失活动力学快两到三倍。激活或稳态失活的电压依赖性以及失活恢复的时间进程没有变化。相比之下，从MB-神经节分离的神经元表达的IA，其幅度、电压依赖性和动力学与对照MB+和OV+神经节的无法区分。因此，与眼中靶组织的相互作用在决定发育中的睫状神经节神经元中IA的特性方面起作用，而节前神经支配不起作用。此外，与MB+和OV+对照相比，在E12 - E14分离的OV-、MB-和OV-/MB-神经元中，IK[Ca]的幅度降低了90 - 100%。在所有这些神经元中，电压激活的钙电流以正常幅度存在。因此，鸡睫状神经节神经元中IK[Ca]的表达受靶组织相互作用和节前神经支配两者的调节。因此，细胞间相互作用对于原位发育的鸡睫状神经节神经元中正常离子通道组合的表达是必需的。
