Extracellular nucleotides modulate renal ion transport. Our previous results in M-1 cortical collecting duct cells indicate that luminal and basolateral ATP via P2Y2 receptors stimulate luminal Ca2+-activated Cl− channels and inhibit Na+ transport. Here we address the mechanism of ATP-mediated inhibition of Na+ transport. M-1 cells had a transepithelial voltage (V te ) of −31.4 ± 1.3 mV and a transepithelial resistance (R te ) of 1151 ± 28 Ωcm2. The amiloride-sensitive short circuit current (I sc ) was −28.0 ± 1.1 μA/cm2. The ATP-mediated activation of Cl− channels was inhibited when cytosolic Ca2+ increases were blocked with cyclopiazonic acid (CPA). Without CPA the ATP-induced [Ca2+]i increase was paralleled by a rapid and transient R te decrease (297 ± 51 Ωcm2). In the presence of CPA, basolateral ATP led to an R te increase by 144 ± 17 Ωcm2 and decreased V te from −31 ± 2.6 to −26.6 ± 2.5 mV. I sc dropped from −28.6 ± 2.4 to −21.6 ± 1.9 μA/cm2. Similar effects were observed with luminal ATP. In the presence of amiloride, ATP was without effect. This reflects ATP-mediated inhibition of Na+ absorption. Lowering [Ca2+]i by removal of extracellular Ca2+ did not alter the ATP effect. PKC inhibition or activation were without effect. Na+ absorption was activated by pHi alkalinization and inhibited by pHi acidification. ATP slightly acidified M-1 cells by 0.05 ± 0.005 pH units, quantitatively not explaining the ATP-induced effect. In summary this indicates that extracellular ATP via luminal and basolateral P2Y2 receptors inhibits Na+ absorption. This effect is not mediated via [Ca2+]i, does not involve PKC and is to a small part mediated via intracellular acidification.
The Journal of Membrane Biology – Springer Journals
Published: Sep 15, 2001
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