Differences in nucleotide effects on intracellular pH, Na+/H+ antiport activity, and ATP-binding proteins in endothelial cells |
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Authors: | Michael Cutaia Doloretta D Dawicki Lisa M Papazian Nancy Parks Ellen Clarke Sharon Rounds |
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Institution: | (1) Veterans Administration Medical Center, Brown University School of Medicine, USA;(2) Pulmonary and Critical Care Section, Providence Veterans Affairs Medical Center, 830 Chalkstone Avenue, 02908 Providence, Rhode Island |
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Abstract: | Summary Bovine (BPAEC) and human (HPAEC) pulmonary artery endothelial cell monolayers were incubated with either ATP, ATP analogues,
or UTP, followed by measurement of intracellular pH (pHi) and the rate of recovery from acidosis. ATP increased baseline pHi
and the rate of acid recovery in BPAEC. This response was inhibited by the amiloride analogue, methyisobutylamiloride, demonstrating
that activation of the Na+/H+ antiport was responsible for the increase in baseline pHi and the recovery from acidosis. This response had the features
of both a P2Y and P2U purinergic receptor, based on the responses to a series of ATP analogues and UTP. In contrast, none of the nucleotides had
any significant effect on pHi and Na+/H+ antiport activity in HPAEC. This difference in the response to extracellular nucleotides was not due to a difference in ATP
metabolism between cell types, since the ectonucleotidase-resistant analogue, ATPγS, also had no effect on HPAEC. Analogues
of cAMP had no effect on pHi or acid recovery in either cell type. Incubation of BPAEC and HPAEC with the photoaffinity ligand
32P] 8-AzATP indicated that both BPAEC and HPAEC possess an ATP-binding protein of 48 kDa. However, BPAEC exhibited an additional
binding protein of 87 kDa. Thus, the contrasting response to extracellular ATP between bovine and human pulmonary artery endothelial
cells may be related to differences in the signal transduction pathway leading to antiport activation, including different
ATP-binding sites on the cell membrane. |
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Keywords: | endothelial cells Na+/H+ antiport intracellular pH extracellular nucleotides purinergic receptors |
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