Add time:08/13/2019         Source:sciencedirect.com

Trichosporin (TS) -B-VIa, a fungal α-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 μM) was completely dependent on the external Ca 2+, while that induced by TS-B-VIa at higher concentrations (10–30 μM) was partly independent of the Ca2+. The concentration-response curves (2–5 μM) for the TS-B-VIa-induced Ca2+ influx and secretion correlated well. The TS-B-VIa (at 5 μM) -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 μM) 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+]; were only slightly observed in Ca2+-free medium, indicating that TS-B-VIa causes Ca 21 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+]i 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 chromaffin cells) and non-excitable cells (the C6 cells and the platelets) and that TS-B-VIa per se may form Ca2+-permeable ion channels in biological membranes. On the other hand, the peptide at the higher concentrations seems to damage cell membranes.

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