Endogenous SNAP-25 Regulates Native Voltage-gated Calcium Channels in Glutamatergic Neurons

Michela Matteoli,Steven B. Condliffe,Irene Corradini,Claudia Verderio,Davide Pozzi

doi:10.1074/jbc.m110.145813

Michela Matteoli, Steven B. Condliffe

Open Access

https://doi.org/10.1074/jbc.m110.145813

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Abstract

In addition to its primary role as a fundamental component of the SNARE complex, SNAP-25 also modulates voltage-gated calcium channels (VGCCs) in various overexpression systems. Although these studies suggest a potential negative regulatory role of SNAP-25 on VGCC activity, the effects of endogenous SNAP-25 on native VGCC function in neurons are unclear. In the present study, we investigated the VGCC properties of cultured glutamatergic and GABAergic rat hippocampal neurons. Glutamatergic currents were dominated by P/Q-type channels, whereas GABAergic cells had a dominant L-type component. Also, glutamatergic VGCC current densities were significantly lower with enhanced inactivation rates and shifts in the voltage dependence of activation and inactivation curves compared with GABAergic cells. Silencing endogenous SNAP-25 in glutamatergic neurons did not alter P/Q-type channel expression or localization but led to increased VGCC current density without changes in the VGCC subtype proportions. Isolation of the P/Q-type component indicated that increased current in the absence of SNAP-25 was correlated with a large depolarizing shift in the voltage dependence of inactivation. Overexpressing SNAP-25 in GABAergic neurons reduced current density without affecting the VGCC subtype proportion. Accordingly, VGCC current densities in glutamatergic neurons from Snap-25(+/-) mice were significantly elevated compared with wild type glutamatergic neurons. Overall, this study demonstrates that endogenous SNAP-25 negatively regulates native VGCCs in glutamatergic neurons which could have important implications for neurological diseases associated with altered SNAP-25 expression.

Highlights

Grant HEALTH F2-2009-241498 (EUROSPIN Project), EUSynapse Integrated Project, Cariplo 2008.2338, Cariplo 2006.0948, and Compagnia di S.Paolo Program 2005.1964
Mean I-V relations demonstrate that Ba2ϩ currents were significantly elevated in GABAergic neurons and peaked at a more depolarized potential compared with peak Ba2ϩ currents in glutamatergic neurons (Fig. 1D), suggesting differences in voltage-dependent gating between voltage-gated calcium channels (VGCCs) currents of glutamatergic and GABAergic neurons
The present study demonstrates that endogenous SNAP-25 negatively regulates native VGCC properties in glutamatergic neurons

Summary

Introduction

Grant HEALTH F2-2009-241498 (EUROSPIN Project), EUSynapse Integrated Project, Cariplo 2008.2338, Cariplo 2006.0948, and Compagnia di S.Paolo Program 2005.1964 If SNAP-25 is physiologically involved in regulating VGCC function, the reduction of endogenous SNAP-25 expression in neurons would remove a regulatory “brake” on calcium channel function, leading to alterations in VGCC properties. This would reveal the physiological role of SNAP-25 in controlling native VGCC function but would have important implications for brain pathologies where the levels of SNAP-25 are altered (9 –11). We found similar increases in VGCC function in glutamatergic neurons from SNAP-25 heterozygous mice These results demonstrate that levels of endogenous SNAP-25 negatively modulate native VGCC function, which could have important consequences for brain diseases characterized by a reduced SNAP-25 expression

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