Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB253

Poster Communications

Role of the CaVβ and the actin cytoskeleton on synaptic transmission in mouse hippocampal neurons

G. Guzman1, R. Guzman1, N. Jordan1, P. Hidalgo1,2

1. Institute of Complex Systems, Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany. 2. Institute of Biochemistry, Heinrich-Heine University Düsseldorf, Düsseldorf, Germany.

Activation of voltage-gated calcium channels (Cav) initiates neurotransmitter release. The neuronal CaV core complex is formed by the CaVα1 ion-conducting and the CaVβ subunits. It is well established that the association of CaVβ with CaVα1 up-regulates calcium currents and that CaVβ interacts with several other partners fulfilling CaV-independent functions. Most recently, we reported that CaVβ associates directly with actin filaments that in synaptic terminals appears to organize synaptic vesicle clusters. Here, we investigated the role of CaVβ, type 4b, and actin cytoskeleton on synaptic transmission in hippocampal neurons from newborn (postnatal day P0-P3) mice using electrophysiological methods in autaptic and continental cultures. We found that exogenously expressed CaVβ4b enhances spontaneous and evoked postsynaptic currents without altering synaptogenesis. Moreover, CaVβ4b increases the readily releasable pool (RRP) size of synaptic vesicles at rest conditions, assessed by hypertonic sucrose application, and accelerates their recovery time after depletion. Either inserting a double mutation in the CaVβ4b that inhibits its association with CaVα1 or disrupting pharmacologically the actin cytoskeleton abolishes the potentiation of synaptic strength induced by CaVβ4b. Thus, CaVβ4b relies on an intact actin cytoskeleton to facilitate the mobilization of synaptic vesicles to a fusion competent state. However, a CaVβ4b mutant with impaired binding to CaVα1 does not alter the time course of the RRP recovery but preserves the ability to increase the RRP size suggesting an alternative path to mobilize synaptic vesicles to the RRP at rest conditions from a pool loosely coupled to the actin cytoskeleton. Altogether our results demonstrate that an interplay between CaVβ and F-actin support synaptic transmission and uncover a new function of the CaVβ that is independent of its association state with CaVα1.

Where applicable, experiments conform with Society ethical requirements