ATP, a partial agonist of atypical P2y purinoceptors in rat brain microvascular endothelial cells

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Abstract
1 Purinoceptor responses were analyzed in B10 cells, a clonal population of rat brain capillary endothelial cells. 2 B10 cells lack P2U receptors as evidenced by the lack of UTP responses and the failure to amplify P2u-related sequences by polymerase chain reaction. 3 B10 cells responded to adenine nucleotides by large increases in [Ca2+]i. Half maximum effective concentrations were 2-methylthio-ATP: 180 nM > 2-chloro-ATP: 310 nM = ADP: 330 nM> adenosine 5′-0-(3-thiotrisphosphate): 2.3 μm = ATP: 2.7 μm. The maximum response to ATP was only 55% of that to ADP while that to ATP derivatives was 75%. 4 The actions of adenine nucleotides were not associated with a measurable activation of phospholipase C. 5 Cross desensitizations of the actions of ADP and ATP were observed. 6 In additivity experiments, ADP superposed its action on top of that of ATP and ATP partially inhibited the action of ADP. 7 It is concluded that ATP acts as a partial agonist of the P2Y-like receptor of brain capillary endothelial cells.