Functional characterization of adenosine receptors and coupling to ATP-sensitive K+ channels in Guinea pig urinary bladder smooth muscle.
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 (K(ATP)) channels. Membrane hyperpolarization evoked by adenosine and various adenosine receptor subtype-selective agonists was attenuated or reversed by the K(ATP) 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) approximately 2-p-(2-carboxethyl)phenethyl-amino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS-21680; 7.65) > 2-chloro adenosine (5.90) approximately 2-chloro-N6-cyclopentyladenosine (CCPA; 5.51) approximately N6-cyclopentyladenosine approximately 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 A(2A)-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 inhibitor N-(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) approximately CGS-21680 (6.38) > 2-chloro adenosine (5.90) >> CCPA approximately 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 A(2A) receptor-mediated activation of K(ATP) channels via adenylate cyclase and elevation of cAMP.
Gopalakrishnan
Sujatha M
SM
Advanced Technology, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois 60064-6181, USA. sujstha.m.gopalakrishnan@abbott.com
Buckner
Steven A
SA
Milicic
Ivan
I
Groebe
Duncan R
DR
Whiteaker
Kristi L
KL
Burns
David J
DJ
Warrior
Usha
U
Gopalakrishnan
Murali
M
D018528:ATP-Binding Cassette Transporters; D000241:Adenosine / Q000494:pharmacology; D000243:Adenosine Deaminase / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D054086:KATP Channels; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D054086:KATP Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; D014665:Vasodilator Agents; C092520:uK-ATP-1 potassium channel; D000243:Adenosine Deaminase; D000262:Adenylyl Cyclases; D000241:Adenosine; D005905:Glyburide