Gershon E, Weigl L, Lotan I, Schreibmayer W, Dascal N
Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Israel.
J Neurosci. 1992 Oct;12(10):3743-52. doi: 10.1523/JNEUROSCI.12-10-03743.1992.
The voltage-dependent Na+ channel of the brain is a good substrate for phosphorylation by the cAMP-dependent protein kinase (protein kinase A, or PKA), but the physiological effects of PKA on Na+ channels are poorly documented. We studied modulation by PKA of voltage-dependent Na+ channels expressed in Xenopus oocytes injected with RNA coding for the alpha-subunit of the channel protein (rat brain type IIA and its variant VA200), using the two electrode voltage-clamp technique. Intracellularly injected cAMP or catalytic subunit of PKA, or extracellularly applied forskolin, inhibited the Na+ current by 20-30%. The effect of cAMP was attenuated by prior injection of PKA inhibitors. Injection of small doses of protein phosphatase 2A increased the Na+ current by 10%, whereas larger doses of protein phosphatase 1 and alkaline phosphatase were without effect. The inhibition by PKA showed little voltage dependence, being only slightly stronger at holding potentials at which the availability of the channels was reduced. The voltage dependence of activation and inactivation processes was not altered by cAMP. Similar effects were exerted by forskolin and cAMP on the Na+ channels expressed after the injection of heterologous (total) RNA from rat brain. Thus, PKA modulates the Na+ channel by a mechanism that does not involve major changes in the voltage dependency of the current and is exerted on the channel-forming alpha-subunit.
大脑中的电压依赖性钠离子通道是环磷酸腺苷（cAMP）依赖性蛋白激酶（蛋白激酶A，即PKA）磷酸化的良好底物，但PKA对钠离子通道的生理作用却鲜有文献记载。我们采用双电极电压钳技术，研究了PKA对注射编码通道蛋白α亚基（大鼠脑IIA型及其变体VA200）RNA的非洲爪蟾卵母细胞中表达的电压依赖性钠离子通道的调节作用。向细胞内注射cAMP或PKA的催化亚基，或向细胞外施加福斯可林，可使钠离子电流抑制20%-30%。预先注射PKA抑制剂可减弱cAMP的作用。注射小剂量的蛋白磷酸酶2A可使钠离子电流增加10%，而大剂量的蛋白磷酸酶1和碱性磷酸酶则无此作用。PKA的抑制作用几乎不依赖电压，仅在通道可用性降低的钳制电位下稍强一些。cAMP并未改变激活和失活过程的电压依赖性。福斯可林和cAMP对注射大鼠脑异源（总）RNA后表达的钠离子通道也有类似作用。因此，PKA通过一种不涉及电流电压依赖性重大变化的机制调节钠离子通道，且该作用作用于形成通道的α亚基。
