Maitotoxin activates cation channels distinct from the receptor-activated non-selective cation channels of HL-60 cells.
We investigated whether maitotoxin activates non-selective cation channels, as was recently proposed [Soergel, Yasumoto, Daly and Gusovsky (1992) Mol. Pharmacol. 41, 487-493]. Stimulation of dibutyryl cyclic AMP-differentiated HL-60 cells with the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP; 0.1 microM), the Ca(2+)-ATPase inhibitor thapsigargin (0.1 microM) or maitotoxin (25 ng/ml) resulted in an increase in cytoplasmic free calcium concentration ([Ca2+]i). Unlike fMLP and thapsigargin, maitotoxin produced no increase in [Ca2+]i in the absence of extracellular Ca2+. The increase in [Ca2+]i induced by fMLP was blocked by pretreatment with pertussis toxin (100 ng/ml for 24 h) but not that induced by maitotoxin. Similarly, the increase in [Ca2+]i produced by fMLP but not that produced by maitotoxin was inhibited by pretreatment with phorbol myristate acetate (100 ng/ml). Both fMLP- and maitotoxin-induced increases in [Ca2+]i were blocked by 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenylethyl)-1H-imid azole hydrochloride (SKF 96365) in a concentration-dependent manner. However, the maitotoxin-induced increase in [Ca2+]i was more sensitive to inhibition by SKF 96365 than the fMLP-induced increase. fMLP-induced increases in [Ca2+]i were blocked by cations with Gd3+ being more effective than Cd2+, whereas for maitotoxin Cd2+ was more effective than Gd3+. Both fMLP and thapsigargin stimulated quenching of Fura-2 fluorescence in the presence of extracellular Mn2+, whereas maitotoxin produced no Mn2+ quenching. Taken together these results suggest that maitotoxin does not stimulate the nonselective cation channel activated by fMLP, but instead activates Ca2+ influx by a different mechanism.
Musgrave
I F
IF
Institut für Pharmakologie, Freie Universität Berlin, Germany.
Seifert
R
R
Schultz
G
G
D003994:Bucladesine / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002412:Cations; D005456:Fluorescent Dyes; D016257:Fura-2; D005682:Gadolinium / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects*; D008345:Manganese / Q000494:pharmacology; D008387:Marine Toxins / Q000494:pharmacology*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D035964:Oxocins; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured; D000095702:Polyether Toxins
D003994:Bucladesine; D002104:Cadmium; D002118:Calcium; D002412:Cations; D005456:Fluorescent Dyes; D016257:Fura-2; D005682:Gadolinium; D007093:Imidazoles; D007473:Ion Channels; D008345:Manganese; D008387:Marine Toxins; D009240:N-Formylmethionine Leucyl-Phenylalanine; D035964:Oxocins; D013729:Terpenes; D013755:Tetradecanoylphorbol Acetate; D019284:Thapsigargin; C020394:maitotoxin; D000095702:Polyether Toxins; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole