Trichosporin-B-III, an alpha-aminoisobutyric acid-containing peptide, causes Ca(2+)-dependent catecholamine secretion from adrenal medullary chromaffin cells.
We examined the effect of trichosporin-B-III, an alpha-aminoisobutyric acid-containing antibiotic peptide consisting of 19 amino acid residues and a phenylalaninol, on catecholamine secretion from cultured bovine adrenal chromaffin cells. Incubation of the cells with trichosporin-B-III (3-20 microM) caused an increase in the secretion of catecholamines. The secretion induced by trichosporin-B-III at low concentrations (3 and 5 microM) was completely dependent on external Ca2+, whereas that induced by higher concentrations (10 and 20 microM) was partly independent of Ca2+. Trichosporin-B-III at low concentration (5 microM) did not increase the release of lactate dehydrogenase, a marker enzyme of cytoplasm, from the cells. In contrast, the peptide at higher concentration (10 microM) increased the release of the enzyme. Trichosporin-B-III also caused both 45Ca2+ influx into the cells and an increase in the intracellular free Ca2+ concentration. The increases in catecholamine secretion and 45Ca2+ influx behaved similarly in relation to trichosporin-B-III concentration (3-10 microM). The time courses of the increases in secretion, 45Ca2+ influx, and intracellular free Ca2+ concentration induced by trichosporin-B-III were also quite similar. Trichosporin-B-III-induced (at 5 microM) secretion was not affected by the elimination of Na+ from the incubation medium or by the addition of tetrodotoxin, a blocker of highly selective voltage-dependent Na+ channels, or hexamethonium, a blocker of nicotinic acetylcholine receptors. On the other hand, both diltiazem (2-200 microM) and nicardipine (1-200 microM), blockers of voltage-dependent Ca2+ channels, inhibited the secretion induced by trichosporin-B-III (5 microM) in a concentration-dependent manner. Trichosporin-B-III-induced (at 5 microM) secretion also was suppressed by the addition of Mn2+ (5 mM) to the medium. The diltiazem (20 microM) inhibition of trichosporin-B-III-induced (at 5 microM) secretion was reversed by increasing the external Ca2+ concentration. These results indicate that trichosporin-B-III causes the secretion of catecholamines from bovine adrenal chromaffin cells by two mechanisms, Ca2+ dependent and Ca2+ independent (only at high concentrations of trichosporin-B-III). Furthermore, these results strongly suggest that trichosporin-B-III, in Ca(2+)-dependent secretion, activates endogenous voltage-dependent Ca2+ channels, or itself forms the channels in the membranes, and induces Ca2+ influx into the cells.
Tachikawa
E
E
Department of Pharmacology, School of Medicine, Iwate Medical University, Japan.
Takahashi
S
S
Furumachi
K
K
Kashimoto
T
T
Iida
A
A
Nagaoka
Y
Y
Fujita
T
T
Takaishi
Y
Y
D000313:Adrenal Medulla / Q000378:metabolism; D000595:Amino Acid Sequence; D000621:Aminoisobutyric Acids / Q000494:pharmacology*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002837:Chromaffin Granules / Q000378:metabolism*; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D036341:Intercellular Signaling Peptides and Proteins; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology
D000621:Aminoisobutyric Acids; D000900:Anti-Bacterial Agents; D015220:Calcium Channels; D002395:Catecholamines; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C056809:trichosporin B-IIIa; C056810:trichosporin B-IIId; C071661:trichosporin B-IIIb; C071663:trichosporin B-IIIc; C100049:2-aminoisobutyric acid; D012964:Sodium; D007770:L-Lactate Dehydrogenase; D004110:Diltiazem; D002118:Calcium