Intracellular Ca 2+ signals evoked by stimulation of nicotinic acetylcholine receptors in SH-SY5Y cells: Contribution of voltage-operated Ca2+ channels and Ca2+ stores

Abstract

Neuronal nicotinic acetylcholine receptors (nAChR) can regulate several neuronal processes through Ca2+ mechanisms. The versatility of nAChR-mediated responses presumably reflects the spatial and temporal characteristics of local changes in intracellular Ca2+arising from a variety of sources. The aim of this study was to analyse the components of nicotine-evoked Ca2+ signals in SH-SY5Y cells, by monitoring fluorescence changes in cells loaded with fluo-3 AM. Nicotine (30 μM generated a rapid elevation in cytoplasmic Ca2+ that was partially and additively inhibited (40%) by α7 and α3β2z.ast; nAChR subtype selective antagonists; α3β4* nAChR probably account for the remaining response (60%). A substantial blockade (80%) by CdCl1 (100 μM) indicates that voltage-operated Ca2+ channels (VOCC) mediate most of the nicotine-evoked response, although the α7 selective antagonist α-bungarotoxin (40 μM further decreased the CdCl2 component. The elevation of intracellular Ca2+ levels provoked by nicotine was sustained for at least 10 min and required the persistent activation of nAChR throughout the response. Intracellular Ca2+ stores were implicated in both the initial and sustained nicotine-evoked Ca2+ responses, by the blockade observed after ryanodine (30 μM and the inositoltriphosphate (IP3)-receptor antagonist, xestospongin-c (10 μM Thus, nAChR subtypes are differentially coupled to specific sources of Ca2+: activation of nAChR induces a sustained elevation of intracellular Ca2+ levels which is highly dependent on the activation of VOCC, and also involves Ca2+ release from ryanodine and IP3-dependent intracellular stores. Moreover, the α7, but not α3β2* nAChR, are responsible for a fraction of the VOCC-independent nicotine-evoked Ca2+ increase that appears to be functionally coupled to ryanodine sensitive Ca2+ stores.