Einhorn, Z., Trapani, J.G., Liu, Q., and Nicolson, T. (2012) Rabconnectin3alpha promotes stable activity of the H+ pump on synaptic vesicles in hair cells. The Journal of neuroscience : the official journal of the Society for Neuroscience. 32(32):11144-11156.
Acidification of synaptic vesicles relies on the vacuolar-type ATPase (V-ATPase) and provides the electrochemical driving
force for neurotransmitter exchange. The regulatory mechanisms that ensure assembly of the V-ATPase holoenzyme on synaptic
vesicles are unknown. Rabconnectin3α (Rbc3α) is a potential candidate for regulation of V-ATPase activity because of its association
with synaptic vesicles and its requirement for acidification of intracellular compartments. Here, we provide the first evidence
for a role of Rbc3α in synaptic vesicle acidification and neurotransmission. In this study, we characterized mutant alleles
of rbc3α isolated from a large-scale screen for zebrafish with auditory/vestibular defects. We show that Rbc3α is localized to basal
regions of hair cells in which synaptic vesicles are present. To determine whether Rbc3α regulates V-ATPase activity, we examined
the acidification of synaptic vesicles and localization of the V-ATPase in hair cells. In contrast to wild-type hair cells,
we observed that synaptic vesicles had elevated pH, and a cytosolic subunit of the V-ATPase was no longer enriched in synaptic
regions of mutant hair cells. As a consequence of defective acidification of synaptic vesicles, afferent neurons in rbc3α mutants had reduced firing rates and reduced accuracy of phase-locked action potentials in response to mechanical stimulation
of hair cells. Collectively, our data suggest that Rbc3α modulates synaptic transmission in hair cells by promoting V-ATPase
activity in synaptic vesicles.