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1136 TABLE 2. Characteristics of P2X homomeric purinoceptors M.ª TERESA MIRAS-PORTUGAL Y COLS.

Receptor Agonists Antagonists Ion Desensi- Major
modulation tization distribution

P2X1 ATP=2MeSATP=Ap6A NF449>TNP-ATP>Ip5I H+? Fast Brain, spinal cord,
Zn2+? smooth muscle, plate-
=a, ß-meATP >MRS2257>PPADS (nM) lets, sympathetic ganglia

>BzATP>ADP Suramin>RB 2 (µM)

P2X2 ATP=ATP?S=MeATP RB 2=NF279, NF770 H+? Slow Brain, spinal cord,
>Ap4A >PPADS=TNP-ATP Zn2+? smooth muscle, sympa-
a, ß-meATP y ADP =BBG=Suramin (µM) Cu2+? thetic ganglia, chroma-
inactives Ca2+? fin cells, retina

P2X3 2MeSATP=ATP= TNP-ATP>MRS2257= Zn2+? Fast Brain, spinal cord,
a,ß-meATP>Ap5A A317491>MRS2159= H+? smooth muscle, sym-
>ADP PPADS (nM)NF279= Ca2+? pathetic ganglia, sensory
NF449>Ip5I=Suramin> neurons
NF023>RB 2 (µM)
A317491, NF110, ANAL. REAL ACAD. NAC. FARM.
phenol red

P2X4 ATP>2MeSATP TNP-ATP>BBG (µM) H+? Slow Brain, spinal cord,
Zn2+? smooth muscle, sym-
a, ß-meATP y ADP phenolphthalein Cd2+? pathetic ganglia, testis,
colon
inactives

Potentiation by

Ivermectin,

Propofol and Cibacron

blue