Table 1.

Adenosine receptors and their functions

Receptor	Subunit	Signaling pathway
Adenosine A1 receptor	Gαi-subunit	Inhibits adenylate cyclase, decreases cAMP formation [20, 38], leading to activation of KATP channels [4, 26, 35, 39] and inactivation of BKCa channels [28]
	Gβγ subunits	Stimulates PLC and increases IP3 [20, 38]
Adenosine A2A receptor	Gαs-subunit	Activates adenylate cyclase and increases cAMP formation [20, 38], leading to activation of KATP channels [27]
	Pertussis toxin insensitive Gα15 and Gα16 proteins	Activates PLC and upregulates IP3 [20]
Adenosine A2B receptor	Gαs-subunit	Stimulates adenylate cyclase, increases cAMP formation [38], leading to activation of KATP channels [27]
	Gq subunit	Activates PLC and upregulates IP3 [38]
Adenosine A3 receptor	Gαi -subunit	Inhibits adenylate cyclase and decreases cAMP [11, 20]
	Gβγ subunits	Increases the activity of PLC and PLD [38]
All		Modulates MAPK [20]

cAMP cyclic adenosine monophosphate, IP₃ inositol 1,4,5-triphosphate, MAPK mitogen-activated protein kinase, PLC phospholipase C, PLD phospholipase D