ATP sensitive potassium channels are involved in adenosine A2 receptor mediated coronary vasodilatation in the dog.
OBJECTIVE
The aim was to determine a role of ATP sensitive potassium (KATP) channels in adenosine A2 receptor mediated coronary vasodilatation in anaesthetised dogs in vivo.


METHODS
Coronary blood flow in the left circumflex coronary artery, aortic pressure, and left ventricular pressure were measured during intracoronary infusions of the drugs into the left circumflex artery.


RESULTS
A non-selective A2 receptor agonist NECA (5'-N-ethylcarboxamidoadenosine) at 10(-10)-10(-8) mol.min-1 before and after an A1 receptor antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) increased coronary blood flow in a dose dependent manner, without affecting other haemodynamic variables. Glibenclamide at 10 micrograms.kg-1.min-1, which did not alter baseline haemodynamic variables, markedly inhibited the increases in coronary blood flow caused by NECA alone and after DPCPX (p < 0.01). A non-selective adenosine receptor antagonist 8-phenyltheophylline abolished the NECA induced increases in coronary blood flow after DPCPX. These results suggest that A2 receptor mediated coronary vasodilatation was mediated largely by opening of KATP channels. Glibenclamide did not alter the increase in coronary blood flow evoked by forskolin or acetylcholine, suggesting that KATP channels may not be involved in coronary vasodilatation induced by activation of adenylate cyclase or guanylate cyclase. Furthermore, DPCPX increased basal coronary blood flow, which was blocked by 8-phenyltheophylline and by glibenclamide, suggesting that it may have unmasked A2 receptor mediated coronary vasodilatation by inhibiting the A1 receptor mediated vasoconstricting action of endogenous adenosine.


CONCLUSIONS
Opening of KATP channels may be involved importantly in adenosine A2 receptor mediated coronary vasodilatation in canine hearts.
Akatsuka
Y
Y
Research Institute of Angiocardiology and Cardiovascular Clinic, Kyushu University School of Medicine, Fukuoka, Japan.
Egashira
K
K
Katsuda
Y
Y
Narishige
T
T
Ueno
H
H
Shimokawa
H
H
Takeshita
A
A
D000109:Acetylcholine / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D003326:Coronary Circulation / Q000187:drug effects*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005905:Glyburide / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D020110:Pinacidil; D015221:Potassium Channels / Q000187:drug effects*; D058915:Purinergic P1 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*; D014970:Xanthines / Q000494:pharmacology
D006146:Guanidines; D015221:Potassium Channels; D058915:Purinergic P1 Receptor Antagonists; D018048:Receptors, Purinergic P2; D014665:Vasodilator Agents; D014970:Xanthines; D005576:Colforsin; D019830:Adenosine-5'-(N-ethylcarboxamide); D020110:Pinacidil; D000255:Adenosine Triphosphate; C051360:1,3-dipropyl-8-cyclopentylxanthine; D013806:Theophylline; C028322:8-phenyltheophylline; D000241:Adenosine; D000109:Acetylcholine; D005905:Glyburide