UTP-preferring P2 receptor mediates inhibition of sodium transport in porcine thyroid epithelial cells.
1. The effects 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 confluent monolayers on permeable supports in Transwell Ussing chambers. 2. 85% of the forskolin (10 microM)-stimulated short-circuit current was inhibited by phenamil (1 microM), 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 unaffected by nucleotides. 4. The order of potency (with EC50 values given in microM) was UTP (0.08)>>ATP (6.3)=uridine 5'-diphosphate (UDP) (6. 6)>2methyl-thio-adenosine-5'-triphosphate (2MeSATP) (84.5)>adenosine 5'-diphosphate (ADP) (147.8)>alpha,beta-methylene ATP (>150)>>adenosine (>1000). 5. P2 receptors mediating inhibition of sodium absorption were present on the apical membrane of the cells since addition of UTP (1-1000 microM) to the basal compartment of the Ussing chambers had little effect while subsequent addition to the apical compartment produced a normal response. 6. Cibachron blue (Reactive blue 2) (1-100 microM), an antagonist at some P2 receptor subtypes, inhibited phenamil sensitive current in a dose dependent manner with half maximal inhibition occurring at 14.25 microM. 7. Suramin (100 microM), pyridoxalphosphate-6-azophenyl-2', 4'-disulphonic acid (PPADS) (100 microM) and pyridoxal 5'-phosphate (P5P) (100 microM) showed only slight competitive antagonism against the response to UTP. 8 These results indicate that a UTP-preferring P2 receptor located on the apical membrane of thyroid epithelial cells mediates inhibition of Na+ absorption.
Bourke
J
J
Department of Physiology and Pharmacology, The University of Queensland, St Lucia, Australia 4072.
Abel
K
K
Huxham
G
G
Cooper
V
V
Manley
S
S
D000818:Animals; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects* / Q000502:physiology; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000187:drug effects* / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects* / Q000502:physiology; D013552:Swine; D013961:Thyroid Gland / Q000187:drug effects* / Q000502:physiology; D014544:Uridine Triphosphate / Q000494:pharmacology* / Q000502:physiology
D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D005576:Colforsin; D000254:Sodium-Potassium-Exchanging ATPase; D014544:Uridine Triphosphate