Localization of SK2 channels relative to excitatory synaptic sites in the mouse developing Purkinje cells.

Carmen Ballesteros-Merino,Carolina Aguado,Masahiko Watanabe,Rafael Lujã¡N,Josã© Martã­Nez-Hernã¡Ndez,John P Adelman

doi:10.3389/fnana.2014.00154

Abstract

Small-conductance, Ca2+-activated K+ (SK) channels regulate neuronal excitability in a variety of ways. To understand their roles in different neuronal subtypes it is important to determine their precise subcellular distribution. Here, we used biochemical, light microscopy immunohistochemical and immunoelectron microscopy techniques, combined with quantitative approaches, to reveal the expression and subcellular localization patterns of SK2 in the developing cerebellum. Using western blots, the SK2 protein showed a progressive increase during postnatal development. At the light microscopic level, SK2 immunoreactivity was very prominent in the developing Purkinje cells (PC), particularly in the molecular layer (ML). Electron microscopy revealed that throughout development SK2 was mostly detected at the extrasynaptic and perisynaptic plasma membrane of dendritic shafts and dendritic spines of PCs. However, there was some localization at axon terminals as well. Quantitative analyses and 3D reconstructions further revealed a progressive developmental change of SK2 on the surface of PCs from dendritic shafts to dendritic spines. Together, these results indicate that SK2 channels undergo dynamic spatial regulation during cerebellar development, and this process is associated with the formation and maturation of excitatory synaptic contacts to PCs.

Highlights

The cerebellum plays a major role in fine motor control, contributes to memory, cognition, and emotional control (Ito, 2001, 2006)
Quantitative analyses and 3D reconstructions further revealed a progressive developmental change of SK2 on the surface of Purkinje cells (PCs) from dendritic shafts to dendritic spines. These results indicate that SK2 channels undergo dynamic spatial regulation during cerebellar development, and this process is associated with the formation and maturation of excitatory synaptic contacts to PCs
We determined the expression, cellular and subcellular locations in which SK2 channels perform their cerebellar functions during development, with particular emphasis to the postnatal development of PCs

Summary

Introduction

The cerebellum plays a major role in fine motor control, contributes to memory, cognition, and emotional control (Ito, 2001, 2006). Intracellular Ca2+ transients mediated by different types of Ca2+ channels are important in both developing and adult PCs (Gruol et al, 1992; Eilers et al, 1996). In PCs, P/Q-type Ca2+ channels that are essential for PC synaptogenesis provide the Ca2+ source for the activation of SK channels (Miyazaki et al, 2004, 2012). This functional coupling between P/Q-type and SK channels is highlighted by the findings that both of these channels have been implicated in cerebellar ataxia (Edgerton and Reinhart, 2003; Womack et al, 2004)

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Conclusion