We examined the mechanisms underlying dendritic calcium accumulation in lob
ula plate tangential cells of the fly visual system using an in vitro prepa
ration of the fly brain. Local visual stimulation evokes a localized calciu
m signal in the dendrites of these cells in vivo. Here we show that a simil
ar localized calcium accumulation can be elicited in vitro by focal iontoph
oretic application of the cholinergic agonist carbachol. The calcium signal
had at least two sources: first, voltage-dependent calcium channels contri
buted to the carbachol-induced signal and were concentrated on the dendrite
, the soma, and the terminal ramification of the axon. However, the dendrit
ic calcium signal induced by carbachol stimulation was only weakly dependen
t on membrane depolarization. The most likely explanation for the second, v
oltage-independent part of the dendritic calcium signal is calcium entry th
rough nicotinic acetylcholine receptors. We found no indication of second-m
essenger or calcium-mediated calcium release from intracellular stores. In
summary, the characteristic spatiotemporal calcium signals in the dendrites
of lobula plate tangential cells can be reproduced in vitro, and result fr
om a combination of voltage- and ligand-gated calcium influx.