Pathway for Ca2+ influx into cells by trichosporin-B-VIa, an alpha-aminoisobutyric acid-containing peptide, from the fungus Trichoderma polysporum.
Trichosporin (TS) -B-VIa, a fungal alpha-aminoisobutyric acid (Aib) -containing peptide consisting of 19 amino acid residues and a phenylalaninol, produced both 45Ca2+ influx into bovine adrenal chromaffin cells and catecholamine secretion from the cells. The secretion induced by TS-B-VIa at lower concentrations (2-5 microM) was completely dependent on the external Ca2+, while that induced by TS-B-VIa at higher concentrations (10-30 microM) was partly independent of the Ca2+. The concentration-response curves (2-5 microM) for the TS-B-VIa-induced Ca2+ influx and secretion correlated well. The TS-B-VIa (at 5 microM) -induced secretion was not antagonized by diltiazem, a blocker of L-type voltage-sensitive Ca2+ channels. The treatment of fura-2-loaded C6 glioma cells with TS-B-VIa (2-5 microM) led to an increase in the intracellular free Ca2+ concentration ([Ca2+]i) in a concentration-dependent manner but the stimulatory effects of TS-B-VIa on [Ca2+]i were only slightly observed in Ca(2+)-free medium, indicating that TS-B-VIa causes Ca2+ influx from the external medium into the C6 cells. The TS-B-VIa-induced increase in [Ca2+]i in the C6 cells was not antagonized by diltiazem and by SK&F 96365, a novel blocker of receptor-mediated Ca2+ entry. High K+ increased neither [Ca2+]1 in the C6 cells nor Mn2+ influx into the cells, while TS-B-VIa increased Mn2+ influx. Also in other non-excitable cells, bovine platelets, similar results were obtained. These results strongly suggest that the mechanism of Ca2+ influx by TS-B-VIa at the lower concentrations is distinct from the event of Ca2+ influx through receptor-operated or L-type voltage-sensitive Ca2+ channels in both excitable cells (the chrornaffin cells) and non-excitable cells (the C6 cells and the platelets) and that TS-B-VIa per se may form Ca(2+)-permeable ion channels in biological membranes. On the other hand, the peptide at the higher concentrations seems to damage cell membranes.
Tachikawa
E
E
Department of Pharmacology, School of Medicine, Iwate Medical University, Morioka, Japan.
Nogimori
K
K
Takahashi
S
S
Mizuma
K
K
Itoh
K
K
Kashimoto
T
T
Nagaoka
Y
Y
Iida
A
A
Fujita
T
T
D000311:Adrenal Glands / Q000187:drug effects / Q000502:physiology; D000621:Aminoisobutyric Acids / Q000032:analysis*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects / Q000502:physiology; D004110:Diltiazem / Q000494:pharmacology; D016232:Endothelins / Q000494:pharmacology; D005656:Fungal Proteins / Q000032:analysis / Q000494:pharmacology*; D005910:Glioma / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D010455:Peptides; D011188:Potassium / Q000494:pharmacology; D014242:Trichoderma / Q000737:chemistry*; D014407:Tumor Cells, Cultured
D000621:Aminoisobutyric Acids; D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D002395:Catecholamines; D016232:Endothelins; D005656:Fungal Proteins; D010455:Peptides; C089061:trichosporin B-VIa; C100049:2-aminoisobutyric acid; D008345:Manganese; D004110:Diltiazem; D011188:Potassium; D002118:Calcium