Muscarinic acetylcholine receptor activation enhances hippocampal neuron excitability and potentiates synaptically evoked Ca2+ signals via phosphatidylinositol 4,5-bisphosphate depletion

Using single cell Ca2+ imaging and whole cell current clamp recordings, this study aimed to identify the signal transduction mechanisms involved in mACh receptor-mediated, enhanced synaptic signaling in primary cultures of hippocampal neurons. Activation of M1 mACh receptors produced a 2.48 ± 0.26-fold enhancement of Ca2+ transients arising from spontaneous synaptic activity in hippocampal neurons. Combined imaging of spontaneous Ca2+ signals with inositol 1,4,5-trisphosphate (IP3) production in single neurons demonstrated that the methacholine (MCh)-mediated enhancement required activated Gq/11α subunits and phospholipase C activity but did not require measurable increases in IP3. Electrophysiological studies demonstrated that MCh treatment depolarized neurons from −64 ± 3 to −45 ± 3 mV and increased action potential generation. Depletion of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2) enhanced neuronal excitability and prolonged the action of MCh. These studies suggest that, in addition to producing the second messengers IP3 and diacylglycerol, mACh receptor activation may directly utilize PIP2 hydrolysis to regulate neuronal excitability.