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VOL. 73 (4), 1127-1157, 2007 PHYSIOLOGICAL ROLE OF EXTRACELLULAR...

astrocytes multiple subtypes of P2Y receptors coexist. One of the
first references about this coexistence is our group’s work in vascular
endothelial cells (75). One data of extreme complexity that can reach
the nucleotide signalling system in neuronal cells is proved by the
presence in cerebellar granular neurons in culture, of most of the
P2Y and P2X receptors cloned so far, furthermore, with preferentially
somatic or axonic/dendritic distribution depending on the receptor
subtype (51, 52). The presence of P2 receptors and their function has
also been studied in neuroblastoma and other tumoral cell lines
from neural origin, where the expression of diverse members of P2Y
and P2X family has also been shown. The complex neural
architecture is also an element to keep in mind concerning the
toxicity, stress and neurodegeneration aspects, since the topographic
distribution of P2X and P2Y receptors is extremely complex and
could generate different responses in neural maintenance and
recuperation. Cerebellar granule neurons have been extensively
studied by our group and a brief summary concerning the presence
and signalling of P2X and P2Y is reported below.

Presence and function of P2X receptors from cultured
cerebellar granule neurons

The presence, distribution and function of P2X receptors have
been extensively studied in the experimental model of cultured
granule neurons obtained from young mice cerebellum. The relative
expression levels of P2X receptors have been analysed by real time
PCR, at 9 div, the most abundant are: P2X4, P2X7, P2X3, P2X2, and
P2X1, and by that order. The mRNA levels correlate well with the
Western blot protein levels, detected with specific antibodies (76).
Microfluorimetric techniques to study the calcium responses with
specific P2X agonists and antagonists show the presence of
functional receptors, being P2X7 and P2X3 the ones most relevant at
the axodendritic fibers, in agreement with their immunocytochemical
localization. Both receptors are able to induce calcium entrance and
calcium dependent exocytotic release, in this case due to the
glutamatergic nature of granule cells, the released neurotransmitter
is glutamate. The intracellular calcium increase also results in
cytoskeletal reorganization mediated by activation of the calcium

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