Adenosine A 1 receptor signaling inhibits BK channels through a PKC α‐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.