Adenosine A(1) receptor signaling inhibits BK channels through a PKCα-dependent mechanism in mouse aortic smooth muscle

Adenosine receptors (AR; A(1), A(2A), A(2B), and A(3)) contract and relax smooth muscle through different signaling mechanisms. Deciphering these complex responses remains difficult because relationships between AR subtypes and various end-effectors (e.g., enzymes and ion channels) remain to be identified. A(1)AR stimulation is associated with the production of 20–hydroxyeicosatetraenoic acid (20–HETE) and activation of protein kinase C (PKC). 20–HETE and PKC can inhibit large conductance Ca(2+)/voltage-sensitive K(+) (BK) channels that regulate smooth muscle contraction. We tested the hypothesis that activation of A(1)AR inhibits BK channels via a PKC-dependent mechanism. Patch clamp recordings and Western blots were performed using aortae of wild type (WT) and A(1)AR knockout (A(1)KO) mice. There were no differences in whole-cell K(+) current or α and β1 subunits expression between WT and A(1)KO. 20–HETE (100 nmol/L) inhibited BK current similarly in WT and A(1)KO mice. NECA (5′–N–ethylcarboxamidoadenosine; 10 μmol/L), a nonselective AR agonist, increased BK current in myocytes from both WT and A(1)KO mice, but the increase was greater in A(1)KO (52 ± 15 vs. 17 ± 3%; P < 0.05). This suggests that A(1)AR signaling negatively regulates BK channel activity. Accordingly, CCPA (2–chloro–N(6)-cyclopentyladenosine; 100 nmol/L), an A(1)AR-selective agonist, inhibited BK current in myocytes from WT but not A(1)KO mice (81 ± 4 vs. 100 ± 7% of control; P < 0.05). Gö6976 (100 nmol/L), a PKCα inhibitor, abolished the effect of CCPA to inhibit BK current (99 ± 3% of control). These data lead us to conclude that, in aortic smooth muscle, A(1)AR inhibits BK channel activity and that this occurs via a mechanism involving PKCα.