DIFFERENCES IN NUCLEOTIDE EFFECTS ON INTRACELLULAR PH, NA+ H+ ANTIPORT ACTIVITY, AND ATP-BINDING PROTEINS IN ENDOTHELIAL-CELLS/

Bovine (BPAEC) and human (HPAEC) pulmonary artery endothelial cell mon olayers were incubated with either ATP, ATP analogues, or UTP, followe d by measurement of intracellular pH (pHi) and the rate of recovery fr om acidosis. ATP increased baseline pHi and the rate of acid recovery in BPAEC. This response was inhibited by the amiloride analogue, methy isobutylamiloride, demonstrating that activation of the Na+/H+ antipor t was responsible for the increase in baseline pHi and the recovery fr om acidosis. This response had the features of both a P-2Y and P-2U pu rinergic receptor, based on the responses to a series of ATP analogues and UTP. In contrast, none of the nucleotides had any significant eff ect on pHi and Na+/H+ antiport activity in HPAEC. This difference in t he response to extracellular nucleotides was not due to a difference i n ATP metabolism between cell types, since the ectonucleotidase-resist ant analogue. ATP(gamma)S, also had no effect on HPAEC.;IEC. Analogues of cAMP had no effect on pHi or acid recovery in either cell type. In cubation of BPAEC and HPAEC with the photoaffinity ligand [P-32] 8-AzA TP indicated that both BPAEC and HPAEC posses an ATP-binding protein o f 48 kDa. However, BPAEC exhibited an additional binding protein of 87 kDa. Thus, the contrasting response to extracellular ATP between bovi ne and human pulmonary artery endothelial cells may be related to diff erences in the signal transduction pathway leading to antiport activat ion, including different ATP-binding sites on the cell membrane.