Junctophilin Proteins Tether a Cav1-RyR2-KCa3.1 Tripartite Complex to Regulate Neuronal Excitability

Giriraj Sahu,Rima-Marie Wazen,Pina Colarusso,S.R Wayne Chen,Gerald W Zamponi,Ray W Turner

doi:10.1016/j.celrep.2019.07.075

Giriraj Sahu, Rima-Marie Wazen + Show 4 more

Open Access

https://doi.org/10.1016/j.celrep.2019.07.075

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Abstract

The excitability of CA1 hippocampal pyramidal cells is mediated by a slow AHP (sAHP) that responds to calcium increases by Cav1 calcium channels and ryanodine receptors (RyR). We used super-resolution and FRET microscopy to investigate the proximity and functional coupling among Cav1.3/Cav1.2, RyR2, and KCa3.1 potassium channels that contribute to the sAHP. dSTORM and FRET imaging shows that Cav1.3, RyR2, and KCa3.1 are organized as a triprotein complex that colocalizes with junctophilin (JPH) 3 and 4 proteins that tether the plasma membrane to the endoplasmic reticulum. JPH3 and JPH4 shRNAs dissociated a Cav1.3-RyR2-KCa3.1 complex and reduced the IsAHP. Infusing JPH3 and JPH4 antibodies into CA1 cells reduced IsAHP and spike accommodation. These data indicate that JPH3 and JPH4 proteins maintain a Cav1-RyR2-KCa3.1 complex that allows two calcium sources to act in tandem to define the activation properties of KCa3.1 channels and the IsAHP.

Highlights

Control of neuronal excitability depends on calcium-dependent afterhyperpolarizations (AHPs) that activate over specific time frames, ranging from rapid spike repolarization to long-duration slow AHPs
Different JPH isoforms are found in brain, with JPH3 and JPH4 abundantly expressed in hippocampal pyramidal neurons at endoplasmic reticulum (ER)-plasma membrane (PM) junction sites (Nishi et al, 2003)
We find that Cav1.3 calcium channels, RyR2, and KCa3.1 potassium channels can form a tripartite complex at the membrane, as detected by direct stochastic optical reconstruction microscopy and fluorescent resonance energy transfer (FRET)

Summary

Introduction

Control of neuronal excitability depends on calcium-dependent afterhyperpolarizations (AHPs) that activate over specific time frames, ranging from rapid spike repolarization (in milliseconds) to long-duration slow AHPs (in seconds) This level of precision is enabled by functional coupling between specific isoforms of calcium-gated potassium channels and the underlying calcium source (Berkefeld and Fakler, 2008; Engbers et al, 2012, 2013b; Marrion and Tavalin, 1998; Vivas et al, 2017). There are isolated reports that Cav calcium channels can interact with ryanodine receptors (RyRs) in hippocampal neurons to release calcium (Kim et al, 2007; Qin et al, 2012; van de Vrede et al, 2007) Such a close interaction implies that RyRs localized to the endoplasmic reticulum (ER) are close enough to the plasma membrane (PM) to interact with Cav calcium channels. Different JPH isoforms are found in brain, with JPH3 and JPH4 abundantly expressed in hippocampal pyramidal neurons at ER-PM junction sites (Nishi et al, 2003)

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