The functional role of acid-sensing channel 3 in urinary bladders

Lisa Adjei1, Sui Guiping2,1, Rong Weifang3,1, Jian-Mei Li1, Changhao Wu1. 1University of Surrey, Guildford, UK, 2Oesophagael Physiology Laboratory, St Thomas Hospital, London, UK, 3Department of Physiology, Shanghai Jiao Tong University, Shanghai, UK

Acid-sensing ion channels (ASIC) are a class of ion-channels that are classically expressed in the neurones to sense extracellular acidification and pain. These molecules are also found in a variety of peripheral tissues as a sensory molecule. Recently several subtypes of ASICs have been identified in the urinary bladders, in particular ASIC3 which is preferentially expressed in the urothelium and has been suggested to have important pathological implications(1). However, the functional role of these channels in the bladder is poorly understood, in particular in native tissue. This study used a recently identified ASIC3-specific activator 2-guanidine-4-methylquinazoline (2GMQ) (2;3) to examine the role of ASIC3 channels in urothelium-mediated smooth muscle contraction and ATP release.

Guinea-pigs (male Dunkin-Hartley 450-550g) were sacrificed with schedule-1 procedure and urothelium-intact smooth muscle strips were isolated from the urinary bladders. The preparation was superfused in a HEPES-buffered Tyrode’s solution and isometric tension was recorded with a tension-transducer via a bridge-amplifier. ATP was measured by sampling the superfusate adjacent to the urothelium and using a luciferin-luciferase assay.

Spontaneous contractions were consistently observed in urothelium-intact smooth muscle strips which were absent in urothelium-denuded smooth muscle strips. 100µM 2GMQ increased the maximum contractile force (µN/mg tissue, median (25%-75% range); control: 364 (213-853); 2GMQ: 499 (339 -1302), n=4 bladders, paired Wilcoxon signed-rank test, p<0.01) and the mean contractions (102µN/mg tissue; control: 102 (57-199); 2GMQ: 120 (60 -312), n=4, p<0.01). ATP release from the tissue was also increased (ATP release pmolels/g tissue/min, median (25%-75% range); control: 6.9 (4.7 – 9.3); 2GMQ: 33.0 (26.4 – 43.4); n=4, p<0.01).

These data provide the first evidence that ASIC3 channels enhance urothelium-mediated smooth muscle contractions and stimulate ATP release in the bladder wall. The latter may exert an autocrine/paracrine effect on both motor and sensory function in the urinary bladder.

References

(1) Sanchez-Freire V, Blanchard MG, Burkhard FC, Kessler TM, Kellenberger S, Monastyrskaya K. Acid-sensing channels in human bladder: expression, function and alterations during bladder pain syndrome. J Urol 2011; 186(4):1509-1516.

(2) Alijevic O, Kellenberger S. Subtype-specific modulation of ASIC function by 2-guanidine-4-methylquinazoline. J Biol Chem 2012.

(3) Yu Y, Chen Z, Li WG, Cao H, Feng EG, Yu F et al. A nonproton ligand sensor in the acid-sensing ion channel. Neuron 2010; 68(1):61-72.