Fig. 4. The apSyn-induced enhancement of neurotransmitter release requires phosphorylation of domain A. (A) Sample recordings of sniffer depolarization induced by C1 firing (10 Hz for 10 seconds) representative of the different experimental groups in which the soma of the C1 neuron paired with C3 was loaded with either wild-type apSyn, apSynASP9, apSynALA9 or GST. (B) Bar graph showing that the mean amplitude of sniffer depolarization recorded after firing of C1 neurons loaded with either apSyn or the pseudophosphorylated apSynASP9 mutant was significantly higher than that recorded after the stimulation of control neurons injected with GST alone. In contrast, the mean sniffer depolarization amplitude measured after stimulation of C1 neurons loaded with the non-phosphorylatable apSynALA9 mutant was not different from that recorded after firing of GST-injected neurons.