ATP release from the human ureter on distension and P2X(3) receptor expression on suburothelial sensory nerves

Abstract

It is not clear how the increase in intraluminal pressure behind an obstructing ureteric calculus causes an increase in action potential frequency in ureteric sensory nerves so the pain messages are transmitted to the brain. It has been proposed that ureteric distension causes urothelial release of ATP, which activates purinoceptors on suburothelial nociceptive sensory nerves. The purpose of this study was to determine whether distension of the human ureter results in the release of ATP and whether the nociceptive P2 receptor, P2X(3), is expressed on suburothelial sensory nerves in the human ureter. Human ureter segments were perfused with Krebs solution and intermittently distended to a range of pressures. Samples of perfusate were collected throughout and the ATP concentration ([ATP]) was determined using a luciferin-luciferase assay. Sections of ureter were stained using antibodies against P2X(3) and capsaicin receptors (TRPV1). [ATP] rose to more than 10 times baseline levels after distension beyond a threshold of 25-30 cmH(2)O. Immunofluorescence studies on consecutive frozen sections showed that suburothelial nerves stained positively for P2X(3) and capsaicin receptors, with no staining in controls. These findings are consistent with the hypothesis that purinergic signalling is involved in human ureteric mechanosensory transduction, leading to nociception.

Fig. 1

Immunofluorescent staining of the suburothelial ureteric nerves. a P2X₃ receptor. b Capsaicin receptor (TRPV1). c P2X₃ receptor pre-absorption control. d No primary antibody control. Scale bar = 50 μm for each figure. U urothelium, S submucosa, arrows indicate suburothelial layer, arrowheads indicate sensory nerves

Fig. 2

A plot of [ATP] measured in aliquots of perfusate taken throughout a typical experiment with sequentially increasing ureteric distension pressures

Fig. 3

[ATP] in perfusate immediately before and after distension grouped in pressure ranges. The mean [ATP] after distension is significantly greater than before distension in each pressure range (**P < 0.01; n ≥ 7 for each group of distensions, error bars represent SEM)