Article date: August 1999
By: John Bourke, Keith Abel, Graham Huxham, Vanessa Cooper, Simon Manley, in Volume 127, Issue 8, pages 1787-1792
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.
85% of the forskolin (10 μM)‐stimulated short‐circuit current was inhibited by phenamil (1 μM), which is a selective antagonist for epithelial type Na+ channels.
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.
The order of potency (with EC50 values given in μM) 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)>α,β‐methylene ATP (>150)>>adenosine (>1000).
P2 receptors mediating inhibition of sodium absorption were present on the apical membrane of the cells since addition of UTP (1–1000 μM) to the basal compartment of the Ussing chambers had little effect while subsequent addition to the apical compartment produced a normal response.
Cibachron blue (Reactive blue 2) (1–100 μM), an antagonist at some P2 receptor subtypes, inhibited phenamil sensitive current in a dose dependent manner with half maximal inhibition occurring at 14.25 μM.
Suramin (100 μM), pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS) (100 μM) and pyridoxal 5′‐phosphate (P5P) (100 μM) showed only slight competitive antagonism against the response to UTP.
These results indicate that a UTP‐preferring P2 receptor located on the apical membrane of thyroid epithelial cells mediates inhibition of Na+ absorption.
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.
85% of the forskolin (10 μM)‐stimulated short‐circuit current was inhibited by phenamil (1 μM), which is a selective antagonist for epithelial type Na+ channels.
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.
The order of potency (with EC50 values given in μM) 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)>α,β‐methylene ATP (>150)>>adenosine (>1000).
P2 receptors mediating inhibition of sodium absorption were present on the apical membrane of the cells since addition of UTP (1–1000 μM) to the basal compartment of the Ussing chambers had little effect while subsequent addition to the apical compartment produced a normal response.
Cibachron blue (Reactive blue 2) (1–100 μM), an antagonist at some P2 receptor subtypes, inhibited phenamil sensitive current in a dose dependent manner with half maximal inhibition occurring at 14.25 μM.
Suramin (100 μM), pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS) (100 μM) and pyridoxal 5′‐phosphate (P5P) (100 μM) showed only slight competitive antagonism against the response to UTP.
These results indicate that a UTP‐preferring P2 receptor located on the apical membrane of thyroid epithelial cells mediates inhibition of Na+ absorption.
British Journal of Pharmacology (1999) 127, 1787–1792; doi:10.1038/sj.bjp.0702733
DOI: 10.1038/sj.bjp.0702733
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