Luminal P2Y2 Receptor-Mediated Inhibition of Na+ Absorption in Isolated Perfused Mouse CCD
ABSTRACT. Extracellular nucleotides regulate renal transport. A luminal P2Y2 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 (Vte), transepithelial resistance (Rte), and fura-2 [Ca2+]i fluorescence were measured. Baseline parameters were Vte, −16.5 ± 1.2 mV; Rte, 80.8 ± 7.1 Ω cm2; and equivalent short-circuit current (Isc), −261.0 ± 25.1 μA/cm2 (n = 45). Amiloride (10 μM) almost completely inhibited Isc to −3.9 ± 3.8 μA/cm2 (n = 10). Luminal ATP (100 μM) reduced Vte from −16.5 ± 2.1 to −12.5 ± 1.93 and increased Rte from 113.1 ± 16.2 to 123.8 ± 16.7 Ω cm2, which resulted in a 31.7% inhibition of amiloride-sensitive Isc (n = 12). Similarly, luminal UTP reversibly reduced Vte from −22.0 ± 2.1 to −13.6 ± 2.1 mV and increased Rte from 48.4 ± 5.3 to 59.2 ± 7.1 Ω cm2, which resulted in 49.1% inhibition of Na+ absorption (n = 6). In parallel, luminal ATP and UTP elevated [Ca2+]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 Isc by 21.8 (n = 14) and 20.1% (n = 8), respectively. Inhibition of luminal nucleotide-induced [Ca2+]i increase by Ca2+ 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 Ca2+-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 P2Y2 receptors, mediate inhibition of amiloride-sensitive Isc in perfused mouse CCD. This inhibition appears to occurs independently of an increase of cytosolic Ca2+.