UTP‐preferring P₂ receptor mediates inhibition of sodium transport in porcine thyroid epithelial cells

Abstract

1 The e ects of adenosine 5'-triphosphate (ATP), uridine 5'-triphosphate (UTP) and analogues on forskolin-stimulated absorption of Na + by porcine thyroid epithelial cells were analysed in cultures grown as con¯uent monolayers on permeable supports in Transwell Ussing chambers. 2 85% of the forskolin (10 mM)-stimulated short-circuit current was inhibited by phenamil (1 mM), which is a selective antagonist for epithelial type Na + channels. 3 Phenamil-sensitive current was inhibited in a dose dependent manner by nucleotides added to the apical compartment of Ussing chambers. In contrast, the phenamil-resistant current, previously shown to represent anion secretion, was una ected by nucleotides. 4 The order of potency (with EC 50 values given in mM) was UTP (0.08)44ATP (6.3)=uridine 5'-diphosphate (UDP) (6.6)42methyl-thio-adenosine-5'-triphosphate (2MeSATP) (84.5)4adenosine 5'-diphosphate (ADP) (147.8)4a,b-methylene ATP (4150)44adenosine (41000). 5 P 2 receptors mediating inhibition of sodium absorption were present on the apical membrane of the cells since addition of UTP (1 ± 1000 mM) to the basal compartment of the Ussing chambers had little e ect while subsequent addition to the apical compartment produced a normal response. 6 Cibachron blue (Reactive blue 2) (1 ± 100 mM), an antagonist at some P 2 receptor subtypes, inhibited phenamil sensitive current in a dose dependent manner with half maximal inhibition occurring at 14.25 mM. 7 Suramin (100 mM), pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (100 mM) and pyridoxal 5'-phosphate (P5P) (100 mM) showed only slight competitive antagonism against the response to UTP. 8 These results indicate that a UTP-preferring P 2 receptor located on the apical membrane of thyroid epithelial cells mediates inhibition of Na + absorption.

Stimulation of rat erythrocyte P2X7 receptor induces the release of epoxyeicosatrienoic acids

“…The role of P2Y receptors was uncovered by inhibition of EET release from the rat erythrocyte in response to UTP, the prototypical P2Y agonist (Kochukov and Ritchie, 2004; Figure 3). Additionally, increased EET release from RBCs produced by suramin at 100 μ M (Table 2) can be explained by selective inhibition of P2Y receptors (King et al ., 1996; Bourke et al ., 1999) that exert a tonic inhibitory effect on EET release. In contrast, inhibition of EET release by RB‐2 (Table 2), a nonselective ATP antagonist, is a function of its capacity to block all P2 receptors.…”

ATP stimulates Cl− secretion and reduces amiloride‐sensitive Na+ absorption in M‐1 mouse cortical collecting duct cells

“…The finding that extracellular ATP inhibits amiloride‐sensitive Na + absorption in M‐1 cells is reminiscent of the reported inhibitory effect of ATP on Na + and Ca 2+ absorption in cultured rabbit connecting tubule and cortical collecting duct cells which is thought to be mediated by PKC activation (Koster et al 1996). An inhibitory effect of ATP on Na + transport has been observed in a variety of tissues including airway epithelia (Mason et al 1991; Iwase et al 1997; Devor & Pilewski, 1999; Ramminger et al 1999; Inglis et al 1999), and thyroid cells (Bourke et al 1999). Thus, the reciprocal regulation of Cl − secretion and Na + absorption by ATP may be a common theme in epithelia.…”

UTP-dependent Inhibition of Na+ Absorption Requires Activation of PKC in Endometrial Epithelial Cells

“…In contrast, more complete inhibition (40-75%) of amiloride-sensitive Na ϩ absorption after UTP was shown in porcine thyroid epithelial cells and airway epithelia (Bourke et al, 1999;Devor and Pilewski, 1999;Ramminger et al, 1999). In these studies, different hypotheses were proposed to account for inhibition of sodium absorption based on experiments where the actions of ATP or UTP on intracellular calcium or PKC activity were investigated.…”