Extracellular ATP inhibits transport in medullary thick ascending limbs: role of P2X receptors

Silva GB, Garvin JL. Extracellular ATP inhibits transport in medullary thick ascending limbs: role of P2X receptors. Am J Physiol Renal Physiol 297: F1168-F1173, 2009. First published August 26, 2009; doi: 10.1152/ajprenal.00325.2009.-Absorption of NaCl by the thick ascending limb (TAL) involves active transport and therefore depends on oxidative phosphorylation. Extracellular ATP has pleiotropic effects, including both stimulation and inhibition of transport and inhibition of oxidative phosphorylation. However, it is unclear whether ATP alters TAL transport and how this occurs. We hypothesized that ATP inhibits TAL Na absorption by reducing Na entry. We measured oxygen consumption in TAL suspensions. ATP reduced oxygen consumption in a concentration-dependent manner. The purinergic (P2) receptor antagonist suramin (300 mu M) blocked the effect of ATP on TAL oxygen consumption (147 +/- 15 vs. 146 +/- 16 nmol O-2.min(-1).mg protein(-1)). In contrast, the adenosine receptor antagonist theophylline did not block the effect of ATP on oxygen consumption. When Na-K-2Cl cotransport and Na/H exchange were blocked with furosemide (100 mu M) plus dimethyl amiloride (100 mu M), ATP did not inhibit TAL oxygen consumption (from 78 +/- 13 to 98 +/- 5 nmol O-2.min(-1).mg protein(-1)). The Na ionophore nystatin (200 U/ml) increased TAL oxygen consumption to a similar extent in both ATP- and vehicle-treated samples (368 +/- 41 vs. 397 +/- 47 nmol O-2.min(-1).mg protein(-1)). The nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl ester (3 mM) blocked the ATP effects on TAL oxygen consumption (157 +/- 10 vs. 165 +/- 15 nmol O-2.min(-1).mg protein(-1)). The P2X-selective receptor antagonist NF023 blocked the effect of ATP on oxygen consumption, whereas the P2X-selective agonist beta-gamma-Me-ATP reduced oxygen consumption in a concentration-dependent manner. We conclude that ATP inhibits Na transport-related oxygen consumption in TALs by reducing Na entry and P2X receptors and nitric oxide mediate this effect.