title: Independent receptors for diadenosine pentaphosphate and ATP in rat midbrain single synaptic terminals.
abstract: Diadenosine pentaphosphate (Ap5A) and adenosine 5'-triphosphate (ATP) stimulate a intrasynaptosomal calcium concentration [Ca(2+)](i) increase via specific purinergic receptors in rat midbrain synaptosomes, although nothing is known about their distribution in presynaptic terminals. A microfluorimetric technique to measure [Ca(2+)](i) increase using the dye FURA-2AM, has permitted study of the presence of dinucleotide and P2X receptors in independent isolated synaptic terminals. Our results demonstrate the existence of three populations of synaptosomes: one with dinucleotide receptors (12%), another with P2X receptors (20%) and a third with both (14%). It has been possible to demonstrate that the activation of these receptors occurs only in the presence of extracellular Ca(2+) and that it is also coupled with voltage-dependent Ca(2+) channels. Finally 54% of the synaptosomes that responded to K(+) did not present any calcium increase mediated by the nucleotides used. In summary, ATP and dinucleotides exhibit specific ionotropic receptors that can coexist or not on the same synaptic terminal.
authors.affiliation: Departamento de Bioquímica y Biología Molecular IV, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Díaz-Hernández
authors.forename: J
authors.initials: J
authors.lastname: Pintor
authors.forename: E
authors.initials: E
authors.lastname: Castro
authors.forename: M T
authors.initials: MT
authors.lastname: Miras-Portugal
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004396:Coloring Agents; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D008297:Male; D008636:Mesencephalon / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011955:Receptors, Drug / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D016708:Synaptophysin / Q000378:metabolism
chemical_list: D004396:Coloring Agents; D015226:Dinucleoside Phosphates; D011955:Receptors, Drug; D018048:Receptors, Purinergic P2; D016708:Synaptophysin; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; C012275:P(1),P(5)-di(adenosine-5'-)pentaphosphate; D011732:Pyridoxal Phosphate; D002118:Calcium