Rab3A Inhibition of Ca²⁺ -Dependent Dopamine Release From PC12 Cells Involves Interaction With Synaptotagmin I

Rab3 and synaptotagmin have been suggested to play important roles in the regulation of neurotransmitter release and, however, the molecular mechanism has not been completely clear. Here, we studied the effects of Rab3A and synaptotagmin I (Syt I) on dopamine release using PC12 cells as a model system. Rab3A was demonstrated to have effects on both Ca²⁺ -independent and Ca²⁺ -dependent dopamine releases from the PC12 cells. Application of Rab3A (up to 2500 nM) gradually decreased the amount of Ca²⁺ -dependently released dopamine, indicating that Rab3A is a negative modulator that was further supported by the increase in dopamine release caused by Rab3A knockdown. Syt I knockdown weakened the Ca²⁺ -dependent dopamine release, suggesting that Syt I plays a positive regulatory role in the cellular process. Treatment of the Syt I-knocked down PC12 cells with Rab3A further decreased Ca²⁺ -dependent dopamine release and, however, the decrease magnitude was significantly reduced compared with that before Syt I knockdown, thus for the first time demonstrating that the inhibitory effect of Rab3A on Ca²⁺ -dependent dopamine release involves the interaction with Syt I. This work has shed new light on the molecular mechanism for Rab3 and synaptotamin regulation of neurotransmitter release. J. Cell. Biochem. 118: 3696-3705, 2017. © 2017 Wiley Periodicals, Inc.