Intracellular calcium level is an important factor influencing ion channel modulations by PLC-coupled metabotropic receptors in hippocampal neurons

Signaling pathways involving phospholipase C (PLC) are involved in various neural functions. Understanding how these pathways are regulated will lead to a better understanding of their roles in neural functions. Previous studies demonstrated that receptor-driven PLC beta activation depends on intracellular Ca2+ concentration ([Ca2+](i)), suggesting the possibility that PLC beta-dependent cellular responses are basically Ca2+ dependent. To test this possibility, we examined whether modulations of ion channels driven by PLC-coupled metabotropic receptors are sensitive to [Ca2+](i) using cultured hippocampal neurons. Muscarinic activation triggered an inward current at -100 mV (the equilibrium potential for K+) in a subpopulation of neurons. This current response was suppressed by pirenzepine (an M-1-preferring antagonist), PLC inhibitor, non-selective cation channel blocker, and lowering [Ca2+](i). Using the neurons showing no response at -100 mV, effects of muscarinic activation on K+ channels were examined at -40 mV. Muscarinic activation induced a transient decrease of the holding outward current. This current response was mimicked and occluded by XE991, an M-current K+ channel blocker, suppressed by pirenzepine, PLC inhibitor and lowering [Ca2+](i), and enhanced by elevating [Ca2+](i). Similar results were obtained when group I metabotropic. glutamate receptors were activated instead of muscarinic receptors. These results clearly show that ion channel modulations driven by PLC-coupled metabotropic receptors are dependent on [Ca2+](i), supporting the hypothesis that cellular responses induced by receptor-driven PLC beta activation are basically Ca2+ dependent. (C) 2013 Elsevier B.V. All rights reserved.