Pharmacological characterization of endothelin-stimulated phosphoinositide breakdown and cytosolic free Ca2+ rise in rat C6 glioma cells.
Because increasing evidence indicates that glial cells are a target of endothelin, we have characterized endothelin-induced phosphoinositide (PI) turnover and Ca2+ homeostasis in C6 glioma cells. Endothelin-1 (ET) increased formation of 3H-inositol phosphate (IP) from PI and elicited an increase in cytosolic free Ca2+ ([Ca2+]i) in rat C6 glioma. In the presence of Li+, the increase in 3H-inositol trisphosphate formation was rapid, reaching its peak at 5 min after stimulation. ET also elicited a rapid and sustained increase in [Ca2+]i in a dose-dependent manner (1-100 nM). The rank orders of efficacy for ET-related peptides in increasing [Ca2+]i were ET = ET-2 greater than sarafotoxin greater than ET-3. Both ET-mediated stimulation of IP formation and [Ca2+]i increase were largely inhibited in the absence of external Ca2+ but unaffected by the depletion of external Na+ and the presence of dihydropyridine derivatives or verapamil. Inorganic Ca2+ channel blockers Cd2+, La3+, and Mn2+ at 1 mM inhibited both responses induced by ET. Cross-desensitization and nonadditivity were observed for both events among ET-related peptides tested, but not between ET and ATP. Pretreatment of cells with pertussis toxin (PTX) attenuated the PI response to ET, but had no effect on ET-elicited [Ca2+]i increase. ET-induced Ca2+ mobilization (measured in Ca(2+)-free medium) was only transient and was inhibited by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate. Moreover, the intracellular Ca2+ pools mobilized by ET and ATP appeared to overlap, as indicated by their partial heterologous desensitization.(ABSTRACT TRUNCATED AT 250 WORDS)
Lin
W W
WW
Biological Psychiatry Branch, National Institute of Mental Health, Bethesda, Maryland 20892.
Kiang
J G
JG
Chuang
D M
DM
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D016232:Endothelins / Q000494:pharmacology*; D005910:Glioma / Q000378:metabolism* / Q000473:pathology; D006868:Hydrolysis; D009994:Osmolar Concentration; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured; D014757:Viper Venoms / Q000494:pharmacology
D016232:Endothelins; D010716:Phosphatidylinositols; D014757:Viper Venoms; C057354:sarafotoxins s6; D000255:Adenosine Triphosphate; D002118:Calcium