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M.ª TERESA MIRAS-PORTUGAL Y COLS. ANAL. REAL ACAD. NAC. FARM.

modulation of P2X receptors by GABA metabotropic receptors can

give a clue to understand neuropathic pain, in which insufficient

GABAB signalling has been involved (55, 57, 59). Although the A1
adenosine and GABAB receptors are among the most abundant
located at a presynaptic level, the presence and effect of other Gi

coupled receptors among the dopamine family (D2, D3, D4) and

glutamatergic metabotropic family (group II and group III) should

be explored in specific brain areas.

PRESENCE AND FUNCTION OF P2 RECEPTORS IN
CULTURED NEURONS

In previous works by our group we proved that P2Y metabotropic
receptors can coexist with P2X ionotropic receptors in neurons, like
Purkinje, neurochromaffin cells from adrenal medulla and in
cerebellar granule neurons (52, 71-74). In endothelial cells and

FIGURE 5. P2X receptor modulation by ionotropic and metabotropic recep-
tors. A) Co-existence of nicotinic and P2X receptors. Agonistic effect on acetylcho-

line nicotinic receptors induces intracellular calcium increase, activation of
CaMKII and as a result inhibition of P2X responses in calcium entrance. B) Co-
existence of metabotropic GABAB and P2X receptors. Agonistic effect on GABAB
receptors coupled to Gi results in an affinity and calcium increase mediated by

P2X receptors agonists.

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