Presence of diverse functional P2X receptors in rat cerebellar synaptic terminals.
Studies in individual synaptic terminals have demonstrated the presence of diverse functional P2X receptors in rat cerebellum. No immunolabelling for P2X1, P2X4, P2X5 and P2X6, and scarce presence of P2X2 were found at the cerebellar synaptic terminals. P2X3 immunolabelling was present in 28% of isolated synaptosomes. At these synaptic terminals, nucleotides as ATP or alpha,beta-meATP induced Ca2+ transients in the presence of extracellular Ca2+, showing homologous and heterologous receptor desensitization in 60% of cases. Ip5I 10 nM did not block responses to alpha,beta-meATP, but inhibition occurred when antagonist concentrations were equal or higher than 100 nM. These data agree with the presence of abundant P2X3 homomeric receptors. P2X7 immunolabelling was present in 60% of terminals and P2X7 receptor hallmarks in Ca2+ responses have been found. BzATP was more potent than ATP and responses were potentiated when assayed in Mg2+-free medium. EC50 values were, respectively, 39.4+/-0.4 and 0.3+/-0.1 microM for ATP in the presence or absence of Mg2+. Maximal values of synaptosomal calcium transients, in the presence or absence of Mg2+, were, respectively, 91.6+/-11.9 and 132.9+/-12.9 nM for ATP; and 104.3+/-9.4 and 169.7+/-17.1 nM for BzATP. In addition, Zn2+ inhibited ATP responses in the absence of Mg2+ and the P2X7 specific antagonist Brilliant Blue G completely blocked these responses in one half of synaptosomes. This study reports the presence of functional P2X3 and P2X7 receptors at synaptic sites, which provides complexity and regulatory possibilities to the cerebellar neurotransmission.
Hervás
Cristina
C
Department of Biochemistry, Veterinary Faculty, Universidad Complutense de Madrid, Avda. Puerta de Hierro s/n, 28040 Madrid, Spain.
Pérez-Sen
Raquel
R
Miras-Portugal
M Teresa
MT
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002531:Cerebellum / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D007150:Immunohistochemistry; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D017729:Presynaptic Terminals / Q000737:chemistry*; D051381:Rats; D017208:Rats, Wistar; D018048:Receptors, Purinergic P2 / Q000032:analysis* / Q000502:physiology; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D058486:Receptors, Purinergic P2X7
C546403:P2rx2 protein, rat; C546410:P2rx3 protein, rat; C546470:P2rx7 protein, rat; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D058486:Receptors, Purinergic P2X7; D000255:Adenosine Triphosphate; D008274:Magnesium; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium