P2X(2) characteristics of the ATP receptor coupled to [Ca2+](i) increases in cultured Purkinje neurons from neonatal rat cerebellum

P2X receptors present in cerebellar Purkinje cells have been studied by rec ording ATP-elicited [Ca2+](i) signals from immuno-identified (calbindin(+)) cells in culture using fura-2 microfluorescence. The [Ca2+](i) increases e voked by ATP were mimicked by 2MeSATP but not by alpha,beta-meATP and other purinoceptor agonists. The selective P2X(1) antagonist diinosine pentaphos phate failed to inhibit ATP-elicited [Ca2+](i) transients, but suramin and PPADS rapidly and reversibly blocked the [Ca2+](i) responses to ATP and 2Me SATP. The IC50 values for suramin and PPADS inhibition were 48.7 +/- 4.4 an d 5.9 +/- 0.3 mu M, respectively. Both antagonists blocked completely the s ignal elicited by ATP, revealing that there was not a separate antagonist-i nsensitive P2X receptor population in Purkinje cells. The effect of ATP was potentiated by Zn2+ and H+ ions. A one unit acidification from pH 7.4 to 6 .4 enhanced by 172% the [Ca2+](i) transient elicited by an intermediate con centration of ATP. Conversely, alkalinization of the medium to pH 8.4 reduc ed the ATP response by 88%. This combination of pharmacological and modulat ory properties indicates that endogenous P2X receptors present in Purkinje neurons are formed by P2X(2) subunits, rather than the more abundantly expr essed P2X(4) purinoceptor subunits. (C) 1999 Elsevier Science Ltd. All righ ts reserved.