Fig. 7.
The adenylyl cyclase/cAMP/protein kinase A (PKA) signaling system mediates DA D1 receptor inhibition ofID. A, Sp-cAMP (20 μm), a membrane-permeable cAMP analog that activates protein kinase A directly, inhibitedID (n = 6) but notIA. B, Forskolin (10 μm), a membrane-permeable stimulator of adenylyl cyclase, also inhibited ID(n = 6). Perfusion of the same neuron with H8 (10 μm), a membrane-permeable PKA inhibitor, increasedID (n = 5).C, The membrane-permeable protein phosphatase inhibitor okadaic acid (100 nm) inhibitedID (n = 4).D, The PKI subunit (1 U/ml) was included in the pipette solution and diffused into the cell when the whole-cell configuration was formed. Once the cAMP/PKA pathway was fully blocked by PKI, indicated as the VGKC reached steady state, the inhibitory effect of SKF 81297 (1 μm) was also blocked (n = 4). E, Perfusion of Rp-cAMP (50 μm), a membrane-permeable cAMP analog with strong inhibitory effects on PKA (n = 5), also blocked the inhibition by SKF 81297 (1 μm). F, This plot summarizes the contribution of each component of the AC/cAMP/PKA pathway to D1R-mediated modulation of VGKC. Perfusion of Sp-Br-cAMP suppresses VGKC by 26 ± 6% (n = 5). Perfusion of forskolin suppresses VGKC by 22 ± 4% (n = 6), whereas perfusion of H8 enhances VGKC by 21 ± 5%. Perfusion of okadaic acid suppresses VGKC by 17 ± 4% (n = 4). VGKCs become resistant to the stimulation of D1R when the cell is treated with either PKI (IRelative = 1.04 ± 0.05;n = 4) or Rp-cAMP (IRelative = 1.02 ± 0.05;n = 5).