cAMP-dependent protein kinase inhibits [alpha]7 nicotinic receptor activity in layer 1 cortical interneurons through activation of D1/D5 dopamine receptors

Key points Protein kinases can modify the function of many proteins including ion channels. However, the role of protein kinase A in modifying nicotinic receptors in the CNS has never been investigated. We showed through whole-cell recordings of layer 1 prefrontal cortical interneurons that [alpha]7 nicotinic responses are negatively modulated by protein kinase A. Furthermore, we show that stimulation of dopamine receptors can similarly attenuate [alpha]7 nicotinic responses through the activation of protein kinase A. These results suggest how the interaction of the cholinergic and dopaminergic systems may influence neuronal excitability in the brain. Phosphorylation of ion channels, including nicotinic acetylcholine receptors (nAChRs), by protein kinases plays a key role in the modification of synaptic transmission and neuronal excitability. [alpha]7 nAChRs are the second most prevalent nAChR subtype in the CNS following [alpha]4[beta]2. Serine 365 in the M3-M4 cytoplasmic loop of the [alpha]7 nAChR is a phosphorylation site for protein kinase A (PKA). D1/D5 dopamine receptors signal through the adenylate cyclase-PKA pathway and play a key role in working memory and attention in the prefrontal cortex. Thus, we examined whether the dopaminergic system, mediated through PKA, functionally interacts with the [alpha]7-dependent cholinergic neurotransmission. In layer 1 interneurons of mouse prefrontal cortex, [alpha]7 nicotinic currents were decreased upon stimulation with 8-Br-cAMP, a PKA activator. In HEK 293T cells, dominant negative PKA abolished 8-Br-cAMP's effect of diminishing [alpha]7 nicotinic currents, while a constitutively active PKA catalytic subunit decreased [alpha]7 currents. In brain slices, the PKA inhibitor KT-5720 nullified 8-Br-cAMP's effect of attenuating [alpha]7 nicotinic responses, while applying a PKA catalytic subunit in the pipette solution decreased [alpha]7 currents. 8-Br-cAMP stimulation reduced surface expression of [alpha]7 nAChRs, but there was no change in single-channel conductance. The D1/D5 dopamine receptor agonist SKF 83822 similarly attenuated [alpha]7 nicotinic currents from layer 1 interneurons and this attenuation of nicotinic current was prevented by KT-5720. These results demonstrate that dopamine receptor-mediated activation of PKA negatively modulates nicotinic neurotransmission in prefrontal cortical interneurons, which may be a contributing mechanism of dopamine modulation of cognitive behaviours such as attent