Involvement of K+ channels in adenosine A2A and A2B receptor-mediated hyperpolarization of porcine coronary artery endothelial cells.
This study investigated the effects of the following adenosine agonists: 5;-ethylcarboxamidoadenosine (NECA), N6-cyclopentyadenosine (CPA) 2-[p-(2-carboxyethyl)]phenylamino-5;N-ethylcarboxamidoadenosine (CGS-21680), and 2-chloroadenosine (CAD) and its antagonist, 4-(2-[7-amino-2-[2-furyl]]1,2,4-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385), a selective A2A adenosine receptor antagonist, and the involvement of the K+ATP and KCa channels on the resting membrane potential (RMP) of confluent monolayers of cultured porcine coronary artery endothelial cells (PCAECs). Adenosine agonists and K+ATP channel openers (pinacidil, cromakalim) hyperpolarized cultured PCAECs. The average RMP was -32.31 +/- 1.2 mV. Adenosine agonists at 10-5 M caused a significant increase in RMP to -65.0 +/- 1.5 mV for CAD (a nonselective adenosine receptor agonist) to -75.9 +/- 1.6 mV for CGS-21680 (a selective A2A receptor agonist) and to -87.0 +/- 3.5 mV for NECA (a nonselective A1/A2A/A2B receptor agonist). Pinacidil and cromakalim at 10 microM increased the membrane potential to -76.2 +/- 1.2 mV and -75.22 +/- 0.12 mV, respectively. The hyperpolarization induced by adenosine receptor agonists and KATP openers was inhibited by an application of the K+ATP channel blocker glibenclamide (10 microM), indicating the involvement of the K+ATP channel in the adenosine-mediated hyperpolarization of PCAECs. Moreover, 1-EB10, a selective opener of the maxi-KCa channel, hyperpolarized PCAECs, and the effect of 1-EB10 was completely blocked by a selective, irreversible blocker of the high conductance KCa (maxi-K) channels (penitrem A), but it only partially blocked the effect of NECA. ZM-241385 has no effect on hyperpolarization elicited by K+ATP and KCa channel openers. However, ZM-241385 significantly blocked the hyperpolarization effect of CAD and CGS-21680. ZM-241385 partially blocked the hyperpolarizing effect of NECA, and a combination of ZM-241385 and penitrem A further blocked the hyperpolarizing effect of NECA. These results further support the involvement of K+ channels in adenosine A2A and A2B receptor-mediated hyperpolarization of PCAECs.
Olanrewaju
Hammed A
HA
Department of Pharmacology, The Brody School of Medicine, East Carolina University, Greenville, North Carolina 27858, USA. olanrewajuh@mail.ecu.edu
Gafurov
B S
BS
Lieberman
E M
EM
D000818:Animals; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1 / Q000502:physiology*; D013552:Swine
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1