Remodeling of inward rectifying K+ currents in rat atrial myocytes by overexpression of A1-adenosine receptors

In rat atrial myocytes GIRK (Kir3) channels can be activated by acetylcholine and adenosine via M2 and A1 receptors coupled to Pertussis-toxin-sensitive G proteins, such as M2R or A1R. Owing to the lower density of A1R, the amplitude of current activated by a saturating concentration (10 μM) of Ado (IK(Ado)) amounts to about 40% of maximum IK(ACh). Adenovirus-driven overexpression of A1R results in an increase in IK(Ado). In a fraction of A1R-overexpressing cells, both ACh and Ado failed to activate GIRK channels. These cells had a large constitutive Ba2+-sensitive inward rectifying background K+ current, which was insensitive to the GIRK channel inhibitor tertiapin (200 nM), suggesting this current component to be carried by IK1 (Kir) channels. This effect of A1R overexpression was reduced by treatment (48 h) with the A1R antagonist DPCPX. siRNA-mediated knockdown of Kir2.1, simultaneously with A1R overexpression, substantially reduced IK1. The mechanisms underlying the upregulation of functional IK1 channels involve activation of the phosphatidylinositol 3-kinase (Pi3K)/Akt (protein kinase B) pathway. Kir2.1 transcripts are not increased in myocytes overexpressing A1R. These data demonstrate that manipulation of the expression level of a G protein-coupled receptor has unpredictable effects on functional expression of proteins that are supposed to be unrelated to the pathway controlled by that GPCR.