Synaptic vesicle glycoprotein 2A modulates vesicular release and calcium channel function at peripheral sympathetic synapses

Abstract

Synaptic vesicle glycoprotein (SV)2A is a transmembrane protein found in secretory vesicles and is critical for Ca 2+‐dependent exocytosis in central neurons, although its mechanism of action remains uncertain. Previous studies have proposed, variously, a role of SV 2 in the maintenance and formation of the readily releasable pool (RRP) or in the regulation of Ca 2+ responsiveness of primed vesicles. Such previous studies have typically used genetic approaches to ablate SV 2 levels; here, we used a strategy involving small interference RNA (si RNA) injection to knockdown solely presynaptic SV 2A levels in rat superior cervical ganglion (SCG) neuron synapses. Moreover, we investigated the effects of SV 2A knockdown on voltage‐dependent Ca 2+ channel (VDCC) function in SCG neurons. Thus, we extended the studies of SV 2A mechanisms by investigating the effects on vesicular transmitter release and VDCC function in peripheral sympathetic neurons. We first demonstrated an si RNA‐mediated SV 2A knockdown. We showed that this SV 2A knockdown markedly affected presynaptic function, causing an attenuated RRP size, increased paired‐pulse depression and delayed RRP recovery after stimulus‐dependent depletion. We further demonstrated that the SV 2A–si RNA‐mediated effects on vesicular release were accompanied by a reduction in VDCC current density in isolated SCG neurons. Together, our data showed that SV 2A is required for correct transmitter release at sympathetic neurons. Mechanistically, we demonstrated that presynaptic SV 2A: (i) acted to direct normal synaptic transmission by maintaining RRP size, (ii) had a facilitatory role in recovery from synaptic depression, and that (iii) SV 2A deficits were associated with aberrant Ca 2+ current density, which may contribute to the secretory phenotype in sympathetic peripheral neurons.