The M muscarinic receptor, in association to M , regulates the neuromuscular PKA molecular dynamics.

Muscarinic acetylcholine receptor 1 subtype (M ) and muscarinic acetylcholine receptor 2 subtype (M ) presynaptic muscarinic receptor subtypes increase and decrease, respectively, neurotransmitter release at neuromuscular junctions. M involves protein kinase A (PKA), although the muscarinic regulation to form and inactivate the PKA holoenzyme is unknown. Here, we show that M signaling inhibits PKA by downregulating Cβ subunit, upregulating RIIα/β and liberating RIβ and RIIα to the cytosol. This promotes PKA holoenzyme formation and reduces the phosphorylation of the transmitter release target synaptosome-associated protein 25 and the gene regulator cAMP response element binding. Instead, M signaling, which is downregulated by M , opposes to M by recruiting R subunits to the membrane. The M and M reciprocal actions are performed through the anchoring protein A kinase anchor protein 150 as a common node. Interestingly, M modulation on protein expression needs M signaling. Altogether, these results describe the dynamics of PKA subunits upon M muscarinic signaling in basal and under presynaptic nerve activity, uncover a specific involvement of the M receptor and reveal the M /M balance to activate PKA to regulate neurotransmission. This provides a molecular mechanism to the PKA holoenzyme formation and inactivation which could be general to other synapses and cellular models.