β Adrenoceptor-induced cholinergic inhibition in human and rat urinary bladders involves the exchange protein directly activated by cyclic AMP 1 favoring adenosine release.

Background And Purpose: The mechanism by which β receptor agonists (e.g. mirabegron) control bladder overactivity may involve adenosine release from human and rat detrusor smooth muscle. Retrograde activation of adenosine A receptors reduces ACh release from cholinergic bladder nerves. β -Adrenoceptors usually couple to adenylyl cyclase. Here we investigated, which of the cAMP targets, protein kinase A or the exchange protein directly activated by cAMP (EPAC) could be involved in this cholinergic inhibition of the bladder.

Experimental Approach: [ H]ACh and adenosine release from urothelium-denuded detrusor strips of cadaveric human organ donors and rats were measured by liquid scintillation spectrometry and HPLC, respectively. In vivo cystometry was also performed in urethane-anaesthetized rats.

Key Results: The exchange protein directly activated by cAMP (EPAC) inhibitor, ESI-09, prevented mirabegron- and isoprenaline-induced adenosine release from human and rat detrusor strips respectively. ESI-09, but not the PKA inhibitor, H-89, attenuated inhibition of [ H]ACh release from stimulated (10 Hz) detrusor strips caused by activating β -adrenoceptors, AC (forskolin) and EPAC1 (8-CTP-2Me-cAMP). Isoprenaline-induced inhibition of [ H]ACh release was also prevented by inhibitors of PKC (chelerythrine and Go6976) and of the equilibrative nucleoside transporter 1 (ENT1; dipyridamole and NBTI), but not by PLC inhibition with U73122. Pretreatment with ESI-09, but not with H-89, prevented the reduction of the voiding frequency caused by isoprenaline and forskolin in vivo.

Conclusion And Implications: Data suggest that β -adrenoceptor-induced inhibition of cholinergic neurotransmission in human and rat urinary bladders involves activation of an EPAC1/PKC pathway downstream cAMP production resulting in adenosine outflow via ENT1.