1 ATP receptors of the P2X class have previously been identi®ed on autonomic nerve endings and on a limited population of CNS neurons. 2 In the present study P2X receptors on mammalian cortical synaptosomes have been identi®ed by a variety of functional and biochemical studies. In choline bu er ATP analogues caused concentration/time dependent Ca 2+ in¯ux. Relative to the e ects caused by ATP, benzoylbenzoyl ATP (BzATP) was about seven times more active than ATP while 2-me-S-ATP and ATPgS were much less active. a,b-me-ATP and b,g-me-ATP were virtually inactive. In sucrose bu er, relative to choline bu er, the activity of BzATP was more than doubled while activity in sodium bu er was reduced. Moreover, the P2X antagonists PPADS or Brilliant Blue G both signi®cantly attenuated in¯ux. These observations suggest the presence of P2X receptors on synaptosomes which subserve Ca 2+ in¯ux. This activity pro®le of the ATP analogues and the response to blocking agents are characteristic of responses of P2X 7 receptors. 3 In¯ux was una ected by the VSCC inhibitors o-CTx-MVIIC and (7) 202 ± 791, indicating that ATP induced Ca 2+ in¯ux occurred primarily through P2X receptors. 4 P2X 7 receptor protein was identi®ed by Western blotting and immunohistochemical staining. Puri®ed preparations were devoid of signi®cant concentrations of GFAP or the microglial marker OX-42 but contained greatly enriched amounts of syntaxin and SNAP 25. 5 The various pharmacological and biochemical studies were all consistent with the presence of functional P2X 7 receptors.

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1 In isolated bladder strips of the rat, a substantial component (46%) of the Ca2"-dependent contractile response to electrical field stimulation (5 Hz) was resistant to combined block of both N and P type Ca2`channels by o-conotoxin-GVIA (300 nM) and co-agatoxin-IVA (100 nM) respectively.2 The resistant portion (non-N, non-P) was sensitive to co-conotoxin-MVIIC (3 gM), which in addition to N and P also blocks Q type channels at this concentration. co-Conotoxin-MVIIC administered alone, inhibited the neurogenic response to the same degree as that observed in the combined presence of coagatoxin-IVA, co-conotoxin-GVIA and o-conotoxin-MVIIC. 3 co-Agatoxin-IVA (100 nM), a concentration that fully inhibits P type channels, had a negligible effect on the neurogenic response. Following blockade of N type Ca2`channels with co-conotoxin-GVIA (300 nM), co-agatoxin-IVA (3 jM) (a concentration well above that used to block P channels, inhibits Q type channels, but spares N type channels), inhibited the residual response to the same degree as cconotoxin-MVIIC alone. 4 Results suggest that neurotransmission in rat urinary bladder is supported by both N and Q type Ca2" channels.

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