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Elevation of cytosolic calcium by cholinoceptor agonists in SH‐SY5Y human neuroblastoma cells: estimation of the contribution of voltage‐dependent currents
Author(s) -
Forsythe Ian D.,
Lambert David G.,
Nahorski Stefan R.,
Linsdell Paul
Publication year - 1992
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1992.tb14488.x
Subject(s) - biophysics , depolarization , chemistry , membrane potential , tetraethylammonium , sh sy5y , resting potential , calcium , reversal potential , agonist , dihydropyridine , muscarinic acetylcholine receptor , patch clamp , endocrinology , potassium , biochemistry , receptor , biology , cell culture , neuroblastoma , genetics , organic chemistry
1 Muscarinic but not nicotinic receptor stimulation in SH‐SY5Y human neuroblastoma cells induces a concentration‐dependent increase in [ 3 H]‐inositol phosphate formation and a biphasic increase in [Ca 2+ ] i . The latter involves release from both an intracellular store and Ca 2+ entry across the plasma membrane. Here we examine the possibility that this agonist‐stimulated Ca 2+ entry occurs indirectly, as a consequence of depolarization. 2 Electrophysiological characterization, by whole cell patch‐clamp techniques revealed that SH‐SY5Y cells possess a tetrodotoxin‐sensitive inward sodium current, a dihydropyridine‐insensitive calcium current and an outward potassium current which was blocked by tetraethylammonium, 4‐aminopyridine and intracellular caesium ions. The outward potassium current showed voltage‐dependent activation and inactivation, similar to that seen for A‐currents. 3 Application of nicotinic agonists evoked an inward current in cells voltage‐clamped at negative holding potentials, but this current rectified, resulting in little or no outward current flow at positive potentials. The mean amplitude at a holding potential of — 60 mV was — 1.14 nA. Extrapolation of the current‐voltage relation gave a reversal potential of +8mV, indicative of a non‐specific cationic permeability. 4 Application of muscarinic agonists had no detectable effect in most of the cells tested. However, in one third of cells studied, a small slowly activating inward current was observed. The mean amplitude of this current at a holding potential of — 60 mV was — 8.3 pA. 5 This study confirms that SH‐SY5Y cells possess voltage‐dependent sodium, potassium and calcium currents. In addition, these cells are strongly depolarized by nicotinic agonists, which produce little change in [Ca 2+ ] i . On the other hand, muscarinic agonists produce profound changes in [Ca 2+ ] i with only a small inward current (depolarization). The contrasting effects of these two cholinoceptor agonists strongly implies that the Ca 2+ entry after muscarinic receptor activation is not primarily due to activation of voltage‐dependent calcium channels.