Intracellular Ca²⁺ signals evoked by stimulation of nicotinic acetylcholine receptors in SH‐SY5Y cells: contribution of voltage‐operated Ca²⁺ channels and Ca²⁺ stores

Journal of Neurochemistry - Tập 81 Số 3 - Trang 606-614 - 2002

Federico Dajas‐Bailador¹, Adrian J. Mogg¹, Susan Wonnacott¹

¹Department of Biology and Biochemistry, University of Bath, Bath, UK

Tóm tắt

Abstract

Neuronal nicotinic acetylcholine receptors (nAChR) can regulate several neuronal processes through Ca²⁺‐dependent 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 α3β2* nAChR subtype selective antagonists; α3β4* nAChR probably account for the remaining response (60%). A substantial blockade (80%) by CdCl₂ (100 µm) indicates that voltage‐operated Ca²⁺ channels (VOCC) mediate most of the nicotine‐evoked response, although the α7 selective antagonist α‐bungarotoxin (40 nm) further decreased the CdCl₂‐ resistant 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.

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