ATP, A PARTIAL AGONIST OF ATYPICAL P-2Y PURINOCEPTORS IN RAT-BRAIN MICROVASCULAR ENDOTHELIAL-CELLS

1 Purinoceptor responses were analyzed in B10 cells, a clonal population of rat brain capillary endothelial cells. 2 B10 cells lack P-2U receptors as evidenced by the lack of UTP responses and the failure to amplify P-2U-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'-O-(3-thiotrisphosphate) : 2.3 mu M=ATP: 2.7 mu M 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 P-2Y-like receptor of brain capillary endothelial cells.