title: Stimulation of A(₂a) adenosine receptor abolishes the inhibitory effect of arachidonic acid on the basolateral 50-pS K channel in the thick ascending limb.
abstract: The basolateral 50-pS K channels are stimulated by a cAMP-dependent pathway and inhibited by cytochrome P-450-omega-hydroxylase-dependent metabolism of arachidonic acid (AA) in the rat thick ascending limb (TAL). We now used the patch-clamp technique to examine whether stimulation of adenosine A(₂a) receptor modulates the inhibitory effect of AA on the basolateral 50-pS K channels in the medullary TAL. Stimulation of adenosine A(₂a) receptor with CGS-21680 or inhibition of phospholipase A₂ (PLA₂) with AACOCF3 increased the 50-pS K channel activity in the TAL. Western blot demonstrated that application of CGS-21680 decreased the phosphorylation of PLA(2) at serine residue 505, an indication of inhibiting PLA₂ activity. In the presence of CGS-21680, inhibition of PLA₂ had no further effect on the basolateral 50-pS K channels. The possibility that CGS-21680-induced stimulation of the basolateral 50-pS K channels was partially achieved by inhibition of PLA₂ in the TAL was also supported by the observation that CGS-21680 had no additional effect in the presence of AACOCF3. Moreover, stimulation of adenosine A(₂a) receptor with CGS-21680 also abolished the inhibitory effect of AA and 20-hydroxyeicosatetraenoic acid (20-HETE) on the 50-pS K channels. The effect of CGS-21680 on AA and 20-HETE-mediated inhibition of the 50-pS K channels was mediated by cAMP because application of membrane-permeable cAMP analog, dibutyryl-cAMP, not only increased the 50-pS K channel activity but also abolished the inhibitory effect of AA and 20-HETE. We conclude that stimulation of adenosine A(₂a) receptor increased the 50-pS K channel activity in the TAL, an effect that is achieved by suppression of PLA₂ activity and 20-HETE-induced inhibition.
authors.affiliation: Dept. of Pharmacology, Harbin Med. Univ., Harbin 150086, China.
authors.forename: Mingxiao
authors.initials: M
authors.lastname: Wang
authors.forename: Hongyu
authors.initials: H
authors.lastname: Sui
authors.forename: Wennan
authors.initials: W
authors.lastname: Li
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Yujie
authors.initials: Y
authors.lastname: Liu
authors.forename: Li
authors.initials: L
authors.lastname: Gu
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Wang
authors.forename: Ruimin
authors.initials: R
authors.lastname: Gu
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D058908:Adenosine A2 Receptor Agonists / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D001095:Arachidonic Acids / Q000494:pharmacology; D015153:Blotting, Western; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008138:Loop of Henle / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010627:Phenethylamines / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A / Q000378:metabolism*
chemical_list: D058908:Adenosine A2 Receptor Agonists; D001095:Arachidonic Acids; D004791:Enzyme Inhibitors; D010627:Phenethylamines; D015221:Potassium Channels; D043705:Receptor, Adenosine A2A; C081565:arachidonyltrifluoromethane; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D016718:Arachidonic Acid; D000241:Adenosine