Neuroscience Graduate Program, Department of Pharmacology, University of Vermont, Burlington, Vermont 05405, USA.
J Neurosci. 2012 Jul 4;32(27):9228-37. doi: 10.1523/JNEUROSCI.6504-11.2012.
The potassium channel Kv1.2 α-subunit is expressed in cerebellar Purkinje cell (PC) dendrites where its pharmacological inhibition increases excitability (Khavandgar et al., 2005). Kv1.2 is also expressed in cerebellar basket cell (BC) axon terminals (Sheng et al., 1994), where its blockade increases BC inhibition of PCs (Southan and Robertson, 1998a). Secretin receptors are also expressed both in PC dendrites and BC axon terminals (for review, see (Yuan et al., 2011). The effect of secretin on PC excitability is not yet known, but, like Kv1.2 inhibitors, secretin potently increases inhibitory input to PCs (Yung et al., 2001). This suggests secretin may act in part by suppressing Kv1.2. Receptor-mediated endocytosis is a mechanism of Kv1.2 suppression (Nesti et al., 2004). This process can be regulated by protein kinase A (PKA) (Connors et al., 2008). Since secretin receptors activate PKA (Wessels-Reiker et al., 1993), we tested the hypothesis that secretin regulates Kv1.2 trafficking in the cerebellum. Using cell-surface protein biotinylation of rat cerebellar slices, we found secretin decreased cell-surface Kv1.2 levels by modulating Kv1.2 endocytic trafficking. This effect was mimicked by activating adenylate cyclase (AC) with forskolin, and was blocked by pharmacological inhibitors of AC or PKA. Imaging studies identified the BC axon terminal and PC dendrites as loci of AC-dependent Kv1.2 trafficking. The physiological significance of secretin-regulated Kv1.2 endocytosis is supported by our finding that infusion into the cerebellar cortex of either the Kv1.2 inhibitor tityustoxin-Kα, or of the Kv1.2 regulator secretin, significantly enhances acquisition of eyeblink conditioning in rats.
钾通道 Kv1.2 α 亚基在小脑浦肯野细胞（PC）树突中表达，其药理学抑制可增加兴奋性（Khavandgar 等人，2005）。Kv1.2 也在小脑篮状细胞（BC）轴突末梢表达（Sheng 等人，1994），其阻断增加 BC 对 PCs 的抑制（Southan 和 Robertson，1998a）。促胰液素受体也在 PC 树突和 BC 轴突末梢表达（综述见（Yuan 等人，2011）。促胰液素对 PC 兴奋性的影响尚不清楚，但与 Kv1.2 抑制剂一样，促胰液素强烈增加对 PCs 的抑制性输入（Yung 等人，2001）。这表明促胰液素可能部分通过抑制 Kv1.2 起作用。受体介导的内吞作用是 Kv1.2 抑制的一种机制（Nesti 等人，2004）。该过程可受蛋白激酶 A（PKA）调节（Connors 等人，2008）。由于促胰液素受体激活 PKA（Wessels-Reiker 等人，1993），我们测试了促胰液素调节小脑 Kv1.2 转运的假设。通过大鼠小脑切片表面蛋白生物素化，我们发现促胰液素通过调节 Kv1.2 内吞转运来降低细胞表面 Kv1.2 水平。该作用可通过用 forskolin 激活腺苷酸环化酶（AC）模拟，并用 AC 或 PKA 的药理学抑制剂阻断。成像研究确定 BC 轴突末梢和 PC 树突为 AC 依赖性 Kv1.2 转运的位置。我们发现，将 Kv1.2 抑制剂 tityustoxin-Kα 或 Kv1.2 调节剂促胰液素注入小脑皮质，显著增强了大鼠眨眼条件反射的获得，这支持了促胰液素调节的 Kv1.2 内吞作用的生理意义。
