The use of pHluorins for optical measurements of presynaptic activity

Genetically encoded reporters for optical measurements of presynaptic activ ity hold significant promise for measurements of neurotransmission within i ntact or semi-intact neuronal networks. We have characterized pH-sensitive green fluorescent protein-based sensors (pHluorins) of synaptic vesicle cyc ling at nerve terminals. pHluorins have a pK similar to 7.1, which make the m ideal for tracking synaptic vesicle lumen pH upon cycling through the pla sma membrane during action potentials. A theoretical analysis of the expect ed signals using this approach and guidelines for future reporter developme nt are provided.