Presence of dinucleotide and ATP receptors in human cerebrocortical synaptic terminals

Human cerebrocortical synaptic terminals elicited concentration-dependent C a2+ transients after Ap(5)A (diadenosine pentaphosphate) and ATP stimulatio n, with EC50 values of 23.44 +/- 3.70 mu M and 11.48 +/- 2.12 mu M, respect ively. The lack of cross-desensitisation and the selective antagonism by Ip (5)I (diinosine pentaphosphate), suggests the activation of a dinucleotide receptor by Ap(5)A, and a P2X receptor by ATP. Ap(5)A Ca2+ transients were partially abolished by omega-conotoxin GVI-A (53%), suggesting the particip ation of a N-type Ca2+ channel in the dinucleotide response. ATP effect on Ca2+ entry was abolished by nicardipine (44%) and by omega-conotoxin CVI-A (52%), suggesting the participation of L- and N-type Ca2+ channels. These d ata suggest that Ap(5)A and ATP activate dinucleotide and P2X receptors, re spectively, in human brain synaptic terminals. (C) 1999 Elsevier Science B. V. All rights reserved.