Muscarinic acetylcholine receptor activation enhances hippocampal neuron excitability and potentiates synaptically evoked Ca 2+ signals via phosphatidylinositol 4,5-bisphosphate depletion

Abstract

Using single cell Ca 2+ 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 M 1 mACh receptors produced a 2.48 ± 0.26-fold enhancement of Ca 2+ transients arising from spontaneous synaptic activity in hippocampal neurons. Combined imaging of spontaneous Ca 2+ signals with inositol 1,4,5-trisphosphate (IP 3) production in single neurons demonstrated that the methacholine (MCh)-mediated enhancement required activated G q/11α subunits and phospholipase C activity but did not require measurable increases in IP 3. 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 (PIP 2) enhanced neuronal excitability and prolonged the action of MCh. These studies suggest that, in addition to producing the second messengers IP 3 and diacylglycerol, mACh receptor activation may directly utilize PIP 2 hydrolysis to regulate neuronal excitability.