Plasma membrane ATP receptors in Trypanosoma cruzi trypomastigotes.

Trypomastigotes of Trypanosoma cruzi were impermeable to exogenous radiolabeled ATP for up to 2 h at 4 degrees C. Radioligand binding assays in the cold showed that trypomastigotes had two populations of saturable ATP receptors (ATP-Rs) and the radioligand interaction was reversed by nonlabeled ATP in concentration-dependent assays. The Kds of high- and low-affinity ATP-Rs were 7.27 x 10(-8) and 4.32 x 10(6)M, respectively. The BmaxS for ATP-R1 and ATP-R2 were 2.05 x 10(-14) and 2.50 x 10(-12) mol/4 x 10(-6) flagellates, respectively, or 3100 ATP-R1 copies per trypomastigote and 376,000 ATP-R2 copies per trypomastigote. ATP,2-methyl-thio-ATP,ITP, and ADP displaced ATP-Rs (IC50s: 2.59 x 10(-6) to 7.84 x 10(-6)M/4 x 10(6) trypomastigotes). UTP, CTP, ADP beta S, Cibacron blue, and azido-ATP were 10-100 times less effective. Atractyloside, adenosine, suramin, cAMP, Basilen blue, and GTP failed to displace T. cruzi ATP-Rs. Infective vertebrate stage trypomastigote ATP-Rs were localized to a family of 63 kDa surface glycopolypeptides and ATP-Rs appeared to be stage-regulated because the noninfective insect epimastigote forms had ATP-Rs with KdS that are not capable of metabolic interactions with host-cell micromolar ATP levels. Trypomastigote ATP-Rs may play an important role in the induction of the process of T. cruzi intracellular parasitosis.