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Activation of muscarinic cholinergic receptors (mAChRs) in SH‐SY5Y neuroblastoma cells potentiates both the influx and efflux of potassium following hypotonic stress
Author(s) -
Foster Daniel J,
Heacock Anne M,
Keep Richard F,
Fisher Stephen K
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.714.1
Subject(s) - efflux , chemistry , osmotic concentration , ouabain , tonicity , muscarinic acetylcholine receptor , endocrinology , biophysics , oxotremorine , osmole , potassium , medicine , receptor , sodium , biochemistry , biology , organic chemistry
Incubation of SH‐SY5Y neuroblastoma cells in buffers rendered increasingly hypotonic by a reduction in NaCl concentration resulted in an enhanced basal efflux of K + (threshold of release, 200 mOsM), but had no effect on K + influx. Addition of oxotremorine‐M (Oxo‐M) potently enhanced K + efflux (EC 50 = 0.45 μM) increasing the threshold of release to 280 mOsM, and elicited a similarly potent, volume‐independent, enhancement of K + influx (EC 50 = 1.35μM). When incubated under hypotonic conditions in which osmolarity was varied by the addition of sucrose to a fixed concentration of NaCl, both basal and Oxo‐M‐stimulated K + influx and efflux were dependent upon osmolarity. Basal and Oxo‐M‐stimulated K + influx (but not K + efflux) were inhibited by inclusion of ouabain or furosemide. In addition to the mAChR, activation of other GPCRs previously implicated in osmolyte release also enhanced both K + efflux and influx under hypotonic conditions. Oxo‐M had no effect on cellular K + content under physiologically relevant reductions in osmolarity (0–15%) unless K + influx was blocked by ouabain and furosemide. The results indicate that, although GPCR activation enhances K + efflux under hypotonic conditions, it also stimulates K + influx, and that this results in retention of K + by the cells. Supported by NS23831 (SKF) and GM007767 (DJF).