Studies on maitotoxin-induced intracellular Ca2+ elevation in Chinese hamster ovary cells stably transfected with cDNAs encoding for L-type Ca2+ channel subunits

Citation
M. Cataldi et al., Studies on maitotoxin-induced intracellular Ca2+ elevation in Chinese hamster ovary cells stably transfected with cDNAs encoding for L-type Ca2+ channel subunits, J PHARM EXP, 290(2), 1999, pp. 725-730
Citations number
24
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
ISSN journal
0022-3565 → ACNP
Volume
290
Issue
2
Year of publication
1999
Pages
725 - 730
Database
ISI
SICI code
0022-3565(199908)290:2<725:SOMICE>2.0.ZU;2-I
Abstract
The aim of the present study was to characterize the role played by differe nt L-type Ca2+ channel subunits in [Ca2+](i) increase induced by maitotoxin (MTX). In the presence of 5 mM extracellular K+, MTX (0.01-0.5 ng/ml) indu ced a significant concentration-dependent increase in Fura-2-monitored [Ca2 +](i) in single Chinese hamster ovary (CHO) cells expressing the alpha(1c) (CHOC alpha 9 cells) or the alpha(1c)beta(3)alpha(2)delta (CHOC alpha 9 bet a 3 alpha 2/delta 4 cells) subunits of voltage-gated Ca2+ channels (VGCCs), whereas the effect was much reduced in wild-type CHO cells lacking VGCCs. In addition, MTX effect on CHOC alpha 9, CHOC alpha 9 beta 3 alpha 2/delta 4, and GH(3) cells (0.01-0.1 ng/ml) was inhibited by the selective L-type C a2+ channel entry-blocker nimodipine (10 mu M); a nimodipine-insensitive co mponent was still present, particularly at high (>1 ng/ml) toxin concentrat ions. In CHOC alpha 9 beta 3 alpha 2/delta 4 cells, depolarizing concentrat ions of extracellular K+ (55 mM) reinforced the [Ca2+](i) increase induced by MTX(0.1 ng/ml), and this effect was prevented by nimodipine (10 mu M). F inally, patch-clamp experiments in CHOC alpha 9 beta 3 alpha 2/delta 4 cell s showed that low MTX concentrations (0.03 ng/ml) induced the occurrence of an inward current at -60 mV, which was completely prevented by Cd2+ (100 m u M) and by nimodipine (10 mu M), whereas the same dihydropyridine concentr ation (10 mu M) failed to prevent the electrophysiological effects of a hig her toxin concentration (3 ng/ml). In conclusion, the results of the presen t study showed that MTX-induced [Ca2+](i) elevation involves two components : 1) an action on L-type VGCCs at the pore-forming alpha(1c) subunit level, which is responsible for the greatest rise of [Ca2+](i); and 2) a VGCC-ind ependent mechanism that is present both in excitable and in nonexcitable ce lls and is responsible for a lower elevation of [Ca2+](i).