Bladder purinergic receptors

Abstract

In rabbits the contractile response of the urinary bladder is only partially due to cholinergic innervation since atropine does not completely block neuronally mediated contractions. In the human bladder this atropine resistance is controversial with some reporting atropine resistance in vitro while others have stated that the atropine resistance is also tetrodotoxin resistant. Results of the present investigation demonstrate that an atropine resistant, tetrodotoxin sensitive contraction can be evoked in some, but not all human bladder strips. Evidence accumulated over the past few decades indicates that this atropine resistant contraction may be mediated by ATP or a related purine compound. Studies presented herein are designed to develop a radioligand assay for this purinergic receptor. Initial studies indicated that the hydrolysis resistant ATP analog beta, gamma methylene ATP offers several advantages over ATP as a potential radioligand. It is only slowly hydrolyzed by endogenous ATPase and does not inhibit the hydrolysis of ATP indicating that it probably does not bind to the active sites of endogenous ATP hydrolyzing enzymes. In addition beta, gamma methylene ATP is 10-100 fold more potent than ATP itself in stimulating contractions of the urinary bladder in-vitro. The radioligand binding assay herein described can be used to quantitate the density of purinergic receptors, an essential step for determining the role of this system in urinary bladder function and dysfunction. Application of this assay could form the foundation for development of a new class of therapeutic agents for the treatment of urinary bladder dysfunction based on modulation of the purinergic nervous system.