Release of ATP from rat urinary bladder mucosa: role of acid, vanilloids and stretch.
OBJECTIVE
ATP, released from urothelial cells, modulates afferent nerve firing from the urinary bladder. Here, we have characterized ATP release from the rat bladder mucosa in response to acid, capsaicin, electrical field stimulation (EFS) and stretch, using agonists and antagonists at transient receptor potential vanilloid receptor 1 (TRPV1) and acid-sensing ion channels (ASICs).


METHODS
Rat mucosal strips (containing urothelium and lamina propria) in Perspex microbaths were superfused with Krebs solution. ATP was measured after exposure of matched strips to acid (pH 6.6-5.0), capsaicin (0.1-10 microM), EFS or stretch (150% of original length).


RESULTS
Median basal ATP release was 3.46 nmol g(-1). The mucosal strips responded to stimuli with potency order (median, IQR): acid (pH 5.6-6.0) 286 (103-555) > 10 microM capsaicin 188 (117-431) > 10 Hz EFS 63.0 (13.3-96.4) > stretch 24.4 (6.73-55.1) nmol ATP g(-1). ATP release in response to acid was pH dependent (P < 0.05). Responses to capsaicin did not desensitize nor were they concentration dependent. TRPV1 antagonist, capsazepine (10 microM) abolished capsaicin-evoked ATP release, and reduced acid-evoked (pH 6.5) release to 30% (P < 0.001). The ASIC channel antagonists gadolinium (0.1 mM) and amiloride (0.3 microM) reduced (P < 0.05) the acid-evoked (pH 6.5) release to 40 and 6.5% respectively. ASIC (ASIC1, ASIC2a, ASIC2b, ASIC3) and two TRPV1 gene products were detected in mucosal and detrusor extracts.


CONCLUSIONS
Capsaicin (at TRPV1) and acid (at both TRPV1 and ASIC) induce ATP release from the rat bladder mucosa. This ATP appears to be principally of urothelial origin. This study highlights the importance of ATP and acid as signalling molecules in modulating bladder function.
Sadananda
P
P
Department of Pharmacology, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia.
Shang
F
F
Liu
L
L
Mansfield
K J
KJ
Burcher
E
E
D062565:Acid Sensing Ion Channels; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006851:Hydrochloric Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D009092:Mucous Membrane / Q000187:drug effects / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
C568269:ASIC3 protein, rat; D062565:Acid Sensing Ion Channels; C568268:Asic1 protein, rat; D009419:Nerve Tissue Proteins; D015222:Sodium Channels; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D000255:Adenosine Triphosphate; D006851:Hydrochloric Acid; D002211:Capsaicin