The Dynamic pH Landscape At The Drosophila NMJ Synaptic Cleft And Its Implication In Neurotransmission

The intricate processes governing cellular pH and its impact on protein and cellular function have been extensively explored. However, our understanding of the pH fluctuations that occur during routine cellular activities and their potential to modulate cell function remains, particularly within the highly dynamic pH landscape of a synapse. Investigating the scale, directionality, and temporal characteristics of these activity-dependent pH fluctuations at synapses is of paramount interest, as it carries profound implications for neurotransmitter release and signal transduction. Employing both empirical and computational modeling methods, our research explores the dynamic pH environment within the synaptic cleft of Drosophila glutamatergic motor neuron Ib terminals during synaptic activity and reveals its significance in modulating neurotransmission. Contrary to popular belief, we discovered that these terminals undergo activity-dependent extracellular alkalinization in response to both single action potentials and burst stimulation. This surprising phenomenon was also observed at the mouse calyx of Held. We found activity-dependent alkalinization to be predominantly driven by Ca2+ movement across the postsynaptic membrane, and by targeting pH indicators to subcellular domains, we identified alkalinization to primarily occur within the cleft.