Astrocytes and endothelial cells are in close contact with each other at th
e blood-brain barrier, where important molecular transports take place. Des
pite these key morphological and functional properties, little is known reg
arding the dynamic signalling processes that occur between these two cell t
ypes. We investigated astrocyte-endothelial cell calcium signalling mechani
sms in a coculture model prepared from primary rat cortical astrocytes and
ECV304 cells. We used flash photolysis of caged inositol-trisphosphate (IP3
) and gentle mechanical stimulation to trigger astrocyte-endothelial cell c
alcium signals and to investigate the underlying propagation mechanisms. Ph
otolytically releasing IP3 in a single cell triggered increases in cytoplas
mic calcium concentration that propagated between astrocytes and endothelia
l cells in either direction. These propagating calcium signals did not cros
s cell-free zones and were not affected by fast superfusion or by the purin
ergic inhibitors apyrase and suramin, indicating that they are communicated
through an intracellular pathway in conjunction with gap junctions. Electr
ophysiological experiments confirmed a tow degree of astrocyte-endothelial
cell electrical cell-to-cell coupling, Mechanical stimulation of a single c
ell also triggered astrocyte-endothelial cell calcium signals but, in contr
ast to the former triggering mode, these signals crossed cell-free zones an
d were significantly inhibited by apyrase, thus indicating the involvement
of an extracellular and purinergic messenger. Astrocyte-endothelial cell ca
lcium signalling also occurred in cocultures prepared with astrocytes and p
rimary rat brain capillary endothelial cells. We conclude that astrocytes a
nd endothelial cells can exchange fast-acting calcium signals (time scale o
f seconds) that can be communicated through an intracellular/gap junctional
pathway and an extracellular purinergic pathway.