Adenosine A₁ receptor signaling inhibits BK channels through a PKCα-dependent mechanism in mouse aortic smooth muscle

Adenosine receptors (AR; A₁, A_2A, A_2B, and A₃) 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. A₁AR 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 Ca²⁺/voltage-sensitive K⁺ (BK) channels that regulate smooth muscle contraction. We tested the hypothesis that activation of A₁AR inhibits BK channels via a PKC-dependent mechanism. Patch clamp recordings and Western blots were performed using aortae of wild type (WT) and A₁AR knockout (A₁KO) mice. There were no differences in whole-cell K⁺ current or α and β1 subunits expression between WT and A₁KO. 20-HETE (100 nM) inhibited BK current similarly in WT and A₁KO mice. NECA (5'-N-ethylcarboxamidoadenosine; 10 μM), a non-selective AR agonist, increased BK current in myocytes from both WT and A₁KO mice, but the increase was greater in A₁KO (52±15 vs. 17±3%; p<0.05). This suggests that A₁AR signaling negatively regulates BK channel activity. Accordingly, CCPA (2-chloro-N(6)-cyclopentyladenosine; 100 nM), an A₁AR-selective agonist, inhibited BK current in myocytes from WT but not A₁KO mice (81±4 vs. 100±7% of control; p<0.05). Gö6976 (100 nM), 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, A₁AR inhibits BK channel activity and that this occurs via a mechanism involving PKCα.