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 (≧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+.
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