Nanoenviroments of the β-Subunit of L-Type Voltage-Gated Calcium Channels in Adult Cardiomyocytes.

Christoph Maack,Petra Eder-Negrin,Michael Kohlhaas,Erick Miranda-Laferte,Yiliam Cruz-Garcia,Kathy Pfeiffer,Cornelia Heindl,Katalin Barkovits,Simone Pickel,Michelle Gulentz,Michaela Kuhn,Katrin Marcus

doi:10.3389/fcell.2021.724778

Abstract

In cardiomyocytes, Ca2+ influx through L-type voltage-gated calcium channels (LTCCs) following membrane depolarization regulates crucial Ca2+-dependent processes including duration and amplitude of the action potentials and excitation-contraction coupling. LTCCs are heteromultimeric proteins composed of the Cavα1, Cavβ, Cavα2δ and Cavγ subunits. Here, using ascorbate peroxidase (APEX2)-mediated proximity labeling and quantitative proteomics, we identified 61 proteins in the nanoenvironments of Cavβ2 in cardiomyocytes. These proteins are involved in diverse cellular functions such as cellular trafficking, cardiac contraction, sarcomere organization and excitation-contraction coupling. Moreover, pull-down assays and co-immunoprecipitation analyses revealed that Cavβ2 interacts with the ryanodine receptor 2 (RyR2) in adult cardiomyocytes, probably coupling LTCCs and the RyR2 into a supramolecular complex at the dyads. This interaction is mediated by the Src-homology 3 domain of Cavβ2 and is necessary for an effective pacing frequency-dependent increase of the Ca2+-induced Ca2+ release mechanism in cardiomyocytes.

Highlights

Ca2+ ions play a very important role as signal transducers in cardiomyocytes
The free cytosolic Ca2+ concentration increases from a resting level of ∼100 nM to ∼1 μM (Marks, 2013). This 10-fold difference is caused by Ca2+ currents through L-type voltage-gated calcium channels (LTCCs) located at the transverse tubules (t-tubules) in the dyadic junctions, which lead to the activation of the ryanodine receptors 2 (RyR2) in the sarcoplasmic reticulum (SR) membrane and the release of high Ca2+ amounts from this compartment
During the preparation of the present manuscript, a similar study using transgenic mice overexpressing in the heart Cavβ2b fused to APEX2, identified diverse proteins in the nanoenvironments of LTCCs (Liu et al, 2020)

Summary

Introduction

Ca2+ ions play a very important role as signal transducers in cardiomyocytes. In these cells, Ca2+ influx through L-type voltage-gated calcium channels (LTCCs) following membrane depolarization regulates crucial processes including duration and amplitude of the action potentials, excitation-contraction coupling and gene expression (Catterall, 2011). The free cytosolic Ca2+ concentration increases from a resting level of ∼100 nM to ∼1 μM (Marks, 2013) This 10-fold difference is caused by Ca2+ currents through LTCCs located at the transverse tubules (t-tubules) in the dyadic junctions, which lead to the activation of the ryanodine receptors 2 (RyR2) in the sarcoplasmic reticulum (SR) membrane and the release of high Ca2+ amounts from this compartment. This process is termed Ca2+-induced Ca2+ release (CICR) and triggers sarcomeric contractions. At positive FFR, a rise in the heart rate enhances CICR leading to a significant increase in the cardiac contractile force (Krishna et al, 2013)

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Conclusion