Stimulation of muscarinic receptor in hippocampal neuron induces characteristic increase in cytosolic free Ca2+ concentration.

Changes in cytosolic free Ca2+ concentration ([Ca2+]i) in response to acetylcholine (ACh) were examined by fura-2 fluorometry in cultured rat hippocampal neurons. ACh (greater than or equal to 10(-5) M) induced an increase in [Ca2+]i composed of fast transient and slow long-lasting phases. Atropine (10(-8) M) abolished the fast component and greatly reduced the slow component. The slow component was selectively blocked by pirenzepine (10(-6) M). The effect of ACh remained partially in a Ca2+-deficient medium where effects of L-glutamate and KCl (50 mM) were abolished. Present results suggest that ACh elevates [Ca2+]i by activation of muscarinic receptor subtypes, one of which is coupled with ion channels and the other of which transduces the ACh binding to mobilization of intracellularly stored Ca2+.