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VOL. 76 (1), 3-22, 2010 CROSS-TALK BETWEEN GLUTAMATE AND NUCLEOTIDE...

in the decrease of ATP-mediated responses observed after L-Glu
exposition. Thus, granule neurons were stimulated with 200 µM ATP
three times at 5 min-intervals. Although both second and third peaks
of calcium resulted slightly reduced compared to the first one (95 ±
12% and 86 ± 11%, respectively), statistical analyses did not reveal
any significant differences between them (Figure 4D).

3.6. CaMKII is involved in the cross-talk between glutamate
3.6. and nucleotide receptors

In order to find a possible mechanism in the cross-talk between
glutamate and nucleotide receptors, we searched within the different
receptors sequences for possible phosphorylation consensus
sequences by protein kinases. Prediction of possible phosphorylation
sites were carried out by using computer programs such as GPS 1.10
(26), Scansite 2.0 and ExPASy (27, 28). Thus, GPS (cut-off value 2.5)
and Scansite (low stringency) analyses identified different residues
in both P2X and P2Y receptors susceptible to be phosphorylated
by CaMKII, whereas ExPASy checked that these residues faced the
cytoplasm (Table 1).

Table 1. Sequences for possible phosphorylation consensus sequences by

protein kinases. Prediction of possible phosphorylation sites were carried out by
using computer programs such as GPS 1.10, Scansite 2.0 and ExPASy.

Receptor Site Sequence GPS Scansite ExPASy

Score Cytoplasmatic

P2X2 Ser-431 PRPCSISAL 4.35 0.56 348-472
P2X3 Thr-382 SDQATVEKQ 0.54 339-397
Thr-388 EKQSTDSGA 3.64 0.58
P2X7 Ser-560 WRFVSQDMA 3.81 0.54 356-595
Ser-23 TRIQSVNYG 3.27 0.59 1-25
P2Y1 Ser-258 LRRKSIYLV 3.08 0.55
P2Y2 Ser-351 RKDLSISSD 3.68 0.49 239-265
P2Y6 Thr-59 RRTLTRSAV 3.38 0.60 309-374

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