Luminal P2Y2 Receptor-Mediated Inhibition of Na+ Absorption in Isolated Perfused Mouse CCD

. Extracellular nucleotides regulate renal transport. A luminal P2Y 2 receptor in mouse cortical collecting duct (CCD) principal cells has been demonstrated elsewhere. Herein the effects of adenosine triphosphate (ATP) and uridine triphosphate (UTP) on electrogenic Na + absorption in perfused CCD of mice kept on a low-NaCl diet were investigated. Simultaneously, transepithelial voltage ( V te ), transepithelial resistance ( R te ), and fura-2 [Ca 2+ ] i fluorescence were measured. Baseline parameters were V te , −16.5 ± 1.2 mV; R te , 80.8 ± 7.1 Ω cm 2 ; and equivalent short-circuit current ( I sc ), −261.0 ± 25.1 μA/cm 2 ( n = 45). Amiloride (10 μM) almost completely inhibited I sc to −3.9 ± 3.8 μA/cm 2 ( n = 10). Luminal ATP (100 μM) reduced V te from −16.5 ± 2.1 to −12.5 ± 1.93 and increased R te from 113.1 ± 16.2 to 123.8 ± 16.7 Ω cm 2 , which resulted in a 31.7% inhibition of amiloride-sensitive I sc ( n = 12). Similarly, luminal UTP reversibly reduced V te from −22.0 ± 2.1 to −13.6 ± 2.1 mV and increased R te from 48.4 ± 5.3 to 59.2 ± 7.1 Ω cm 2 , which resulted in 49.1% inhibition of Na + absorption ( n = 6). In parallel, luminal ATP and UTP elevated [Ca 2+ ] i in CCD, increasing the fura-2 ratio by 2.7 ± 0.7 and 4.0 ± 1.2, respectively. Basolateral ATP and UTP (100 μM) also inhibited amiloride-sensitive I sc by 21.8 ( n = 14) and 20.1% ( n = 8), respectively. Inhibition of luminal nucleotide-induced [Ca 2+ ] i increase by Ca 2+ store depletion with cyclopiazonic acid (3 μM) did not affect nucleotide-mediated inhibition of Na + transport ( n = 7). No evidence indicated the activation of a luminal Ca 2+ -activated Cl − conductance, a phenomenon previously shown in M-1 CCD cells ( J Physiol 524: 77–99, 2000). In essence, these data indicate that luminal ATP and UTP, most likely via P2Y 2 receptors, mediate inhibition of amiloride-sensitive I sc in perfused mouse CCD. This inhibition appears to occurs independently of an increase of cytosolic Ca 2+ .