Stimulation of Ca super(2+) influx through ATP receptors on rat brain synaptosomes: identification of functional P2X sub(7) receptor subtypes

• Published in: British journal of pharmacology 2002-04, Vol.135 (7), p.1616-1626
• Main Authors: Lundy, P M, Hamilton, M G, Mi, L, Gong, W, Vair, C, Sawyer, T W, Frew, R
• Format: Article
• Language: English
• ISSN: 0007-1188

ATP receptors of the P2X class have previously been identified on autonomic nerve endings and on a limited population of CNS neurons. In the present study P2X receptors on mammalian cortical synaptosomes have been identified by a variety of functional and biochemical studies. In choline buffer ATP analogues caused concentration/time dependent Ca super(2+) influx. Relative to the effects caused by ATP, benzoylbenzoyl ATP (BzATP) was about seven times more active than ATP while 2-me-S-ATP and ATP gamma S were much less active. alpha , beta -me- ATP and beta , gamma -me-ATP were virtually inactive. In sucrose buffer, relative to choline buffer, the activity of BzATP was more than doubled while activity in sodium buffer was reduced. Moreover, the P2X antagonists PPADS or Brilliant Blue G both significantly attenuated influx. These observations suggest the presence of P2X receptors on synaptosomes which subserve Ca super(2+) influx. This activity profile of the ATP analogues and the response to blocking agents are characteristic of responses of P2X sub(7) receptors. Influx was unaffected by the VSCC inhibitors omega -CTx-MVIIC and (-) 202-791, indicating that ATP induced Ca super(2+) influx occurred primarily through P2X receptors. P2X sub(7) receptor protein was identified by Western blotting and immunohistochemical staining. Purified preparations were devoid of significant concentrations of GFAP or the microglial marker OX-42 but contained greatly enriched amounts of syntaxin and SNAP 25. The various pharmacological and biochemical studies were all consistent with the presence of functional P2X sub(7) receptors.