Fast calcium and voltage-sensitive dye imaging in enteric neurones reveal calcium peaks associated with single action potential discharge

Slow changes in [Ca2+](i) reflect increased neuronal activity. Our study demonstrates that single-trial fast [Ca2+](i) imaging (>= 200 Hz sampling rate) revealed peaks each of which are associated with single spike discharge recorded by consecutive voltage-sensitive dye (VSD) imaging in enteric neurones and nerve fibres. Fast [Ca2+](i) imaging also revealed subthreshold fast excitatory postsynaptic potentials. Nicotine-evoked [Ca2+](i) peaks were reduced by.-conotoxin and blocked by ruthenium red or tetrodotoxin. Fast [Ca2+](i) imaging can be used to directly record single action potentials in enteric neurones. [Ca2+](i) peaks required opening of voltage-gated sodium and calcium channels as well as Ca2+ release from intracellular stores.