Abstract
Although multiple adenosine receptors have been identified, the subtype and underlying mechanisms involved in the relaxation response to adenosine in the urinary bladder remain unclear. The present study investigates changes in the membrane potential, as assessed by fluorescence-based techniques, of bladder smooth muscle cells by adenosine receptor agonists acting via ATP-sensitive potassium (KATP) channels. Membrane hyperpolarization evoked by adenosine and various adenosine receptor subtype-selective agonists was attenuated or reversed by the KATP channel blocker glyburide. Comparison of adenosine receptor agonist potencies eliciting membrane potential effects showed a rank order of potency 5′-N-ethyl-carboxamido adenosine (NECA; −log EC50 = 7.97) ∼ 2-p-(2-carboxethyl)phenethyl-amino-5′-N-ethylcarboxamidoadenosine hydrochloride (CGS-21680; 7.65) > 2-chloro adenosine (5.90) ∼ 2-chloro-N6-cyclopentyladenosine (CCPA; 5.51) ∼N6-cyclopentyladenosine ∼N6-(R)-phenylisopropyladenosine > 2-chloro- N6-(3-iodobenzyl)-adenosine-5′-N-methyl-carboxamide (2Cl-IBMECA; 4.78). Membrane potential responses were mimicked by forskolin, a known activator of adenylate cyclase, and papaverine, a phosphodiesterase inhibitor. The A2A-selective antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino] ethyl)phenol (ZM-241385), and the adenylate cyclase inhibitorN-(cis-2-phenyl-cyclopentyl) azacyclotridecan-2-imine-hydrochloride (MDL-12330A) inhibited the observed change in membrane potential evoked by adenosine and adenosine-receptor agonists. The rank order potency for relaxation of K+-stimulated guinea pig bladder strips, NECA (−log EC50 = 6.41) ∼ CGS-21680 (6.38) > 2-chloro adenosine (5.90) ≫ CCPA ∼ 2Cl-IBMECA (>4.0) was comparable to that obtained from membrane potential measurements. Collectively, these studies demonstrate that adenosine-evoked membrane hyperpolarization and relaxation of bladder smooth muscle is mediated by A2A receptor-mediated activation of KATP channels via adenylate cyclase and elevation of cAMP.
Footnotes
- Abbreviations:
- KATP channel
- ATP-sensitive K+ channel
- FLIPR
- fluorescent imaging plate reader
- ZM-241385
- 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol
- MECA
- 5′-N-methylcaboxamido adenosine
- P1075
- N-cyano-N′-(1,1-dimethylpropyl)-N"-3-pyridylguanidine
- CPA
- N6-cyclopentyl adenosine
- CCPA
- 2-chloro-N6-cyclopentyladenosine
- R-PIA
- (R)-N6-phenylisopropyladenosine
- CGS-21680
- 2-p-(2-carboxethyl)phenethyl-amino-5′-N-ethylcarboxamidoadenosine hydrochloride
- NECA
- 5′-N-ethyl-carboxamido adenosine
- CPCA
- 5′(N-cyclopropyl)-carboxamido adenosine
- DPCPX
- 8-cyclopentyl-3,7-dihydro-1,3-dipropyl-1H-purine-2,6-dione
- CGS-15943
- 9-chloro-2-(2-furyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine
- MDL-12330A
- N-(cis-2-phenyl-cyclopentyl) azacyclotridecan-2-imine-hydrochloride
- 2Cl-IBMECA
- 2-chloro-N6-(3-iodobenzyl)-adenosine-5′-N-methyl-carboxamide
- Received October 4, 2001.
- Accepted November 19, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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