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Voltage‐Sensitive Calcium Channels in Differentiated Neuroblastoma × Glioma Hybrid (NG108–15) Cells: Characterization by Quin 2 Fluorescence
Author(s) -
NoronhaBlob L.,
Richard C.,
U'Prichard D. C.
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb03020.x
Subject(s) - veratridine , tetrodotoxin , nimodipine , chemistry , dihydropyridine , biophysics , calcium , agonist , voltage dependent calcium channel , divalent , extracellular , tetraethylammonium , depolarization , sodium channel , sodium , biochemistry , biology , receptor , potassium , organic chemistry
Depolarization of differentiated neuroblastoma × glioma (NG108–15) cells with KC1 (50 m M ) or veratridine (50 μM ) stimulated Ca 2+ accumulation, was detected by quin 2 fluorescence. Intracellular Ca 2+ concentrations ([Ca 2+ ] i ) were elevated about threefold from 159 ± 7 to 595 ± 52 n M (n = 12). Ca 2+ entry evoked by high extracellular K + concentration ([K + ] o ) was voltage‐dependent and enhanced by the dihydropyridine agonists, BAY K 8644 and CGP 28 392, in a dose‐dependent manner. CGP 28 392 was less potent and less efficacious than BAY K 8644. The (+) and (‐) stereoisomers of 202–791 showed agonist and antagonist properties, respectively. (+)‐202–791 was less potent, but as efficacious as BAY K 8644. In the absence of KCl, BAY K 8644 had no effect on Ca 2+ entry. Voltage‐sensitive calcium channel (VSCC) activity was blocked by organic Ca 2+ channel antagonists (nanomolar range) both before and after KC1 treatment and also by divalent metal cations (micromolar range). High [K + ] o ‐in‐duced Ca 2+ accumulation was dependent on external Ca 2+ , but not on external Na + ions ([Na] o ), and was insensitive to both tetrodotoxin (3 μM ) and tetraethylammonium (10 μM ). In contrast, veratridine‐induced Ca 2+ accumulation required [Na + ] o , and was blocked by tetrodotoxin, but not by nimodipine (1 μM ). Veratridine‐induced Ca 2+ accumulation was slower (∼45 s), smaller in magnitude (∼30% of [K + ] o ‐induced Ca 2+ entry), and also enhanced by BAY K 8644 (∼50%). VSCC were identified in neuronal hybrid (NG108–15 and NCB‐20) cells, but not in glial (C6BU‐1), renal epithelial (MDCK), and human astrocytoma (1321N1) cells. NG108–15 cells differentiated with 1.0 mM dibutyryl cyclic AMP showed greater VSCC activity than undifferentiated cultures. These results suggest that cultured neural cells provide a useful system to study Ca 2+ regulation via ion channels.