SEARCH · PubMed Health

Results for “AMINOISOBUTYRIC ACID”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources

PubMed1998

A search for extraterrestrial amino acids in carbonaceous Antarctic micrometeorites.

Antarctic micrometeorites (AMMs) in the 100-400 microns size range are the dominant mass fraction of extraterrestrial material accreted by the Earth today. A high performance liquid chromatography (HPLC) based technique exploited at the limits of sensitivity has been used to search for the extraterrestrial amino acids alpha-aminoisobutyric acid (AIB) and isovaline in AMMs. Five samples, each containing about 30 to 35 grains, were analyzed. All the samples possess a terrestrial amino acid component, indicated by the excess of the L-enantiomers of common protein amino acids. In only one sample (A91) was AIB found to be present at a level significantly above the background blanks. The concentration of AIB (approximately 280 ppm), and the AIB/isovaline ratio (> or = 10), in this sample are both much higher than in CM chondrites. The apparently large variation in the AIB concentrations of the samples suggests that AIB may be concentrated in rare subset of micrometeorites. Because the AIB/isovaline ratio in sample A91 is much larger than in CM chondrites, the synthesis of amino acids in the micrometeorite parent bodies might have involved a different process requiring an HCN-rich environment, such as that found in comets. If the present day characteristics of the meteorite and micrometeorite fluxes can be extrapolated back in time, then the flux of large carbonaceous micrometeorites could have contributed to the inventory of prebiotic molecules on the early Earth.

Amino Acids↗

PubMed1972

The effects of amino acids on albumin synthesis by the isolated perfused rat liver.

Albumin synthesis was measured in the isolated perfused rat liver by using the livers of both well-fed and starved rats. Starvation markedly decreased albumin synthesis. The livers from starved rats were unable to increase synthesis rates after the addition to the perfusates of single amino acids or the addition of both glucagon and tryptophan. Arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine, added together to ten times their normal peripheral blood concentrations, restored synthesis rates to normal. The plasma aminogram (i.e. the relative concentrations, of amino acids) was altered by depriving rats of protein for 48h. The use of blood from the deprived rats as perfusate, instead of normal blood, decreased albumin synthesis rates significantly by livers obtained from well-fed rats. The addition of single amino acids, including the non-metabolizable amino acid, alpha-aminoisobutyric acid, to the above mixture increased albumin synthesis rates to normal values. It is concluded that amino acids play an important role in the control of albumin synthesis and that more than one mechanism is probably involved.

Albumins↗

PubMed1983

Non-metabolizable amino acids are potent stimulators of hepatic and renal ornithine decarboxylase activity.

The non-metabolizable amino acids alpha-aminoisobutyric acid (AIB) and cycloleucine and the poorly metabolizable amino acid D-alanine potently stimulated hepatic ornithine decarboxylase (ODC) activity in starved rats. The stimulation by AIB was shown to have several of the characteristics of stimulation by a protein meal and occurred in hypophysectomized animals. AIB also stimulated renal, but not brain or heart, ODC activity.

Alanine↗

PubMed1977

Effects of cyclic AMP and dibutyryl cyclic AMP on amino acid transport in the isolated rat ovary.

Prepubertal rat ovaries were incubated in medium containing the non-utilizable amino acids alpha-aminoisobutyric acid (AIB-14C) or 1-aminocyclo-pentane-carboxylic acid (cycloleucine-14C). The rate of uptake of the two amino acids was studied in the isolated ovaries after different incubation periods. Addition of 5mM cyclic AMP (cAMP) caused a slight stimulation of the AIB-transport but in higher concentrations (10-25 mM) an inhibition was noted. With dibutyrl cyclic AMP (dbcAMP) a dose-dependent increase was seen with 0.5-5 mM concentrations with no further effect of higher concentrations. Time course studies were performed with both AIB and cycloleucine in presence of 10 mM dbcAMP and increased uptake values were noted at each time studied (30-240 min). The phosphodiesterase inhibitor aminophyline in lower concentrations did not influence AIB-transport but 5-10 mM caused increased uptake values in the ovaries. The stimulatory action of dbcAMP on amino acid transport was augmented by a low concentration of aminophylline (0.5 mM). Experiments were in addition carried out in the presence of puromycin and under these circumstances it was still possible to enhance amino acid transport by addition of dbcAMP. The results are discussed in relation to earlier reported effects of gonadotropins on ovarian amino acid transport.

Amino Acids↗

PubMed1990

Effect of indomethacin on materno-fetal amino acid transfer in the dual-perfused human placental cotyledon.

Indomethacin (1, 10 and 100 mumol L-1) was incrementally infused (8 min for each concentration) into the maternal and fetal circulations of dual-perfused human placental lobules, and measurements were made of materno-fetal amino acid transfer (using the non-metabolizable amino acid alpha-aminoisobutyric acid, or AIB) and fetal effluent perfusate prostaglandin (PG) E levels. No significant changes in AIB transfer compared with controls were observed at any of the doses of indomethacin infused. There was, however, a significant dose-dependent reduction compared with controls in PGE in the fetal circulation with the infusion of indomethacin.

Amino Acids↗

PubMed1982

Placental amino acid uptake. VI. Regulation by intracellular substrate.

Amino acid uptake by human placental tissue is regulated by intracellular amino acids. alpha-Aminoisobutyric acid (AIB) uptake was reduced at intracellular AIB concentrations of 0.8 mM. The magnitude of reduction increased sharply between 1 and 3 mM and reached a maximum of 45% at 5 mM. Suppression was specific to the "A" system. It occurred only when both the amino acid used for preloading and that used as an uptake substrate were active with that system. In the "L" system, facilitation apparently occurs, and in the "ASC" system there is no apparent effect. The system specificity as well as other evidence indicated that suppression is caused by substrate present intracellularly rather than by dilution of extracellular substrate. Suppression was independent of inhibitors of protein synthesis and was not seen in membrane vesicles prepared from preloaded tissue, indicating that intracellular substrate interacts directly with the carrier (transinhibition) rather than altering its synthesis or degradation. The A system transinhibition has the potential to regulate syncytial uptake in vivo and limit variation due to changes in maternal plasma amino acid concentration.

Amino Acids↗

PubMed1987

Insulin stimulates amino acid transport by alveolar type II epithelial cells in primary culture.

The present experiments were designed to investigate the effect of insulin on amino acid transport by alveolar type II epithelial cells isolated from adult rats. The initial rates of amino acid transport were determined by measuring the uptake of the nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB). Alveolar type II epithelial cells transported AIB by a sodium-dependent process that displayed saturable kinetics. Insulin stimulated transport of 0.1 mM AIB (82.3 +/- 15.0%, mean +/- SE, n = 4) with a half-maximally effective insulin concentration of 2.2 +/- 1.0 ng/ml (mean +/- SE), which is within the physiologic range of rat serum insulin concentration. Kinetic analysis of AIB transport showed that insulin increased the Vmax from 6.7 +/- 1.2 nmol/10(6) cells/min to 9.3 +/- 1.8 nmol/10(6) cells/min and had no effect on the Km value (5.2 +/- 0.8 mM). Alpha-(methylamino) isobutyric acid, a specific substrate for amino acid transport system A, inhibited both the sodium-dependent and insulin-modulated transport of AIB. Thus, alveolar type II epithelial cells transport amino acids in a sodium-dependent process and insulin stimulates this transport. The present study indicates that insulin may play a physiologic role in regulating amino acid transport in alveolar type II epithelial cells.

Amino Acids↗

PubMed1990

Sodium-dependent neutral amino acid transport by human liver plasma membrane vesicles.

The activities of several selected Na(+)-dependent amino acid transporters were identified in human liver plasma membrane vesicles by testing for Na(+)-dependent uptake of several naturally occurring neutral amino acids or their analogs. Alanine, 2-(methylamino)isobutyric acid, and 2-aminoisobutyric acid were shown to be almost exclusively transported by the same carrier, system A. Kinetic analysis of 2-(methylamino)isobutyric acid uptake by the human hepatic system A transporter revealed an apparent Km of 0.15 mM and a Vmax of 540 pmol.mg-1 protein.min-1. Human hepatic system A accepts a broad range of neutral amino acids including cysteine, glutamine, and histidine, which have been shown in other species to be transported mainly by disparate carriers. Inhibition analysis of Na(+)-dependent cysteine transport revealed that the portion of uptake not mediated by system A included at least two saturable carriers, system ASC and one other that has yet to be characterized. Most of the glutamine and histidine uptake was Na(+)-dependent, and the component not mediated by system A constituted system N. The largest portion of glycine transport was mediated through system A and the remainder by system ASC with no evidence for system Gly activity. Our examination of Na(+)-dependent amino acid transport documents the presence of several transport systems analogous to those described previously but with some notable differences in their functional activity. Most importantly, the results demonstrate that liver plasma membrane vesicles are a valuable resource for transport analysis of human tissue.

Adult↗

PubMed1989

Damaging action of photodynamic treatment in combination with hyperthermia on transmembrane transport in murine L929 fibroblasts.

Photodynamic treatment of murine L929 fibroblasts with hematoporphyrin derivative caused inhibition of the 2-aminoisobutyric acid transport system. This was reflected by an increase in the apparent Km with a constant Vmax, indicating impairment of the carrier function rather than a decrease of the number of transport sites. Hyperthermic treatment of these cells resulted in a moderate decrease of the activity of the 2-aminoisobutyric acid transport system. Overall protein synthesis was severely inhibited both by photodynamic treatment and by hyperthermia. Hyperthermia subsequent to photodynamic treatment resulted in an additive inhibition of 2-aminoisobutyric acid transport and of protein synthesis. After photodynamic treatment both 2-aminoisobutyric acid transport and protein synthesis were repaired. The repair of 2-aminoisobutyric acid transport depended on protein synthesis, as shown by the virtually complete blockage of repair by anisomycin. After hyperthermia (either alone or subsequent to photodynamic treatment), no recovery of 2-aminoisobutyric acid transport was observed, although protein synthesis was restored to the initial level. Apparently, hyperthermia subsequent to photodynamic treatment blocks the repair of photodynamically induced damage of this transport system. The experimental results further indicate that protein synthesis is not the rate-determining step for the repair of 2-aminoisobutyric acid transport, although it is necessary in this process. Cell survival was decreased both by photodynamic treatment and by hyperthermia. The combined effects of these two treatments were additive. It is discussed that these results indicate that photodynamic inhibition of 2-aminoisobutyric acid transport is not causally related to loss of clonogenicity, contrary to earlier suggestions.

Aminoisobutyric Acids↗

PubMed1981

The involvement of the membrane oxidoreduction system in stimulating amino acid uptake in Ehrlich ascites tumor cells.

The addition of 5 mM ascorbate plus 0.09 mM phenazine methosulfate stimulated 2- to 3-fold the initial rate of 2-aminoisobutyric acid transport into Ehrlich cells. This was observed under the conditions in which glycolysis and mitochondrial electron transport were blocked by iodoacetate and KCN, and the cellular ATP level was maintained below 0.1 mM. Proton conductors, carbonylcyanide m-chlorophenylhydrazone and SF6847 did not affect the stimulation of 2-aminoisobutyric acid uptake caused by ascorbate plus phenazine methosulfate. Ascorbate was replaced by NADH but not by NADPH, and phenazine methosulfate was the only effective acceptor in stimulating 2-aminoisobutyric acid uptake. The stimulating effect of ascorbate plus phenazine methosulfate was due to an increase in the V value for 2-aminoisobutyric acid but not in the Km value. This effect required the presence of an Na+ gradient and was accompanied by an increase in 22Na+ influx. The molar ratio of 2-aminoisobutyric acid to Na+ uptake enhanced by ascorbate plus phenazine methosulfate was calculated to be 1 : 1. Quinacrine, an inhibitor of NADH oxidoreductase in the plasma membrane, inhibited both the enhanced rate of 2-aminoisobutyric acid and Na+ transport without affecting the basal transport activity. The stimulatory effect of ascorbate plus phenazine methosulfate was also observed with other amino acids, alanine, glycine, proline and cycloleucine which are known to be transported via an Na+-dependent system but not with leucine and threonine. These results suggest that a redox system in the plasma membrane participates in energy coupling for amino acid transport by increasing the rate of cotransport with Na+.

Adenosine Triphosphate↗

PubMed1982

Amino acid uptake and energy coupling dependent on photosynthesis in Anacystis nidulans.

The photoautotrophic cyanobacterium Anacystis nidulans was used to investigate the membrane transport of branched-chain, neutral amino acids and its dependence on photosynthetic reactions. The uptake of alpha-amino [1-14C]isobutyric acid and L-[1-14C]leucine followed Michaelis, Menten kinetics and resulted in an energy-dependent accumulation. As in bacteria, different uptake systems for neutral amino acids were present: two DAG (D-alanine, aminoisobutyric acid, and glycine) systems responsible for uptake of alpha-amino [1-14C]isobutyric acid, and one LIV (leucine, isoleucine, and valine) system, responsible for uptake of leucine. The low-affinity DAG system seemed to be dependent on the presence of Na+ ions. Uptake was enhanced by white light and by monochromatic light of 630 nm. In far red light (717 nm) with and without nitrogen flushing, considerable uptake dependent on light intensity and inhibition by dibromothymoquinone and by high concentrations of KCN were observed. Therefore, the energy generated by photosystem I reactions only could perform this membrane transport. The proton translocator carbonylcyanide m-chlorophenylhydrazone and N,N-dicyclohexylcarbodiimide as an ATPase inhibitor reduced amino acid uptake to a high degree. A pH dependence of aminoisobutyric acid and leucine uptake was obvious, with a maximum at pH 6 to 7 and some at a pH as high as 9.5. At higher pH, increasing concentrations of Na+ K+ and also of triphenylmethylphosphonium ions inhibited the transport of aminoisobutyric acid. These findings are consistent with the assumption that ATP from photosynthetic reactions drives a membrane-bound proton-translocating ATPase producing a proton motive force, consisting at higher pH chiefly in a delta psi amount, which promotes a secondary active H+ or Na+/amino acid symport carrier.

Amino Acids↗

PubMed1978

Inhibition by colchicine of changes in amino acid transport and initiation of DNA synthesis in regenerating rat liver.

The uptake of amino acids (measured with alpha-aminoisobutyric acid) by hepatocytes stimulated to proliferate by partial hepatectomy followed a biphasic pattern, with an initial peak 8-10 hr after surgery followed by a release of amino acids between 10 and 16 hr and a further increase between 16 and 20 hr after the operation. The second period of increased uptake coincided with the increase in DNA synthesis by the hepatocytes. Colchicine, and other microtubule disrupters administered at the time of partial hepatectomy, abolished the first period of increased amino acid uptake and prevented the cells from initiating DNA synthesis. Pulse-labeling experiments with alpha-aminoisobutyric acid revealed that colchicine did not inhibit amino acid transport per se, but prevented the increased capacity for amino acid transport induced by partial hepatectomy. An injection of colchicine 14 hr after hepatectomy prevented the release of amino acids by the liver and also substantially reduced the initiation of DNA synthesis. The data suggest that the microtubules may play a role in proliferative activation and also in the initiation of DNA synthesis of hepatocytes in vivo and that changes in amino acid transport are linked to these microtubule-requiring processes.

Amino Acids↗

PubMed1982

Polarized amino acid transport by an epithelial cell line of renal origin (LLC-PK1). The basolateral systems.

The transport of three neutral amino acid analogs has been studied in an epithelial cell line from a pig kidney. 2-Aminoisobutyric acid is accumulated by LLC-PK1 cells against a concentration gradient through a mechanism with several features of a carrier-mediated process. The influx is accounted for by a saturable Na+-dependent and nonsaturable Na+-independent process. The total influx of 2-(methylamino)isobutyric acid is also mediated through Na+-dependent and Na+-independent systems. Part of the Na+-dependent influx of 2-aminoisobutyric acid was competitively inhibited by 2-(methylamino)isobutyric acid (Ki = 4.2 mM).l Selectivity studies indicate that the 2-(methylamino)isobutyric acid-sensitive part of 2-aminoisobutyric acid influx is mediated through the A system, whereas the insensitive part occurs through the ASC system. Cycloleucine transport also involves a Na+-dependent and Na+-independent process. The Na+-dependent influx is completely inhibited by 2-aminoisobutyric acid but not perceptibly by 2-(methylamino)isobutyric acid. This influx probably represents entry through the ASC system. The Na+-independent component is completely inhibited by 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid, a specific substrate for the L system. Uptake studies from either side of the monolayers indicate that these transport systems are exclusively located in basolateral membranes of the cultured renal cells.

Amino Acids↗

PubMed1966

Discrimination of single transport systems. The Na plus-sensitive transport of neutral amino acids in the Ehrlich cell.

Uptake of methionine, alpha-aminoisobutyric acid, and alpha-(methyl-amino)-isobutyric acid has been shown to occur by at least two transport systems, one sensitive and the other insensitive to the Na(+) concentration. For alpha-aminoisobutyric acid and its N-methyl derivative, the Na(+)-insensitive uptake is not concentrative and its rate increases almost linearly with concentration within the range examined. In contrast, the Na(+)-insensitive uptake of methionine is concentrative and subject to inhibition by such amino acids as phenylalanine, leucine, and valine, although not in a manner to indicate that the uptake is mediated by a single agency. This component is not produced by a residual operation of the Na(+)-requiring transport system, handicapped by the absence of Na(+) or by its having combined with alpha-aminoisobutyric acid. The increase in the rate of methionine uptake is linear with concentration only above about 16 mM methionine. The Na(+)-sensitive uptakes of methionine, alpha-aminoisobutyric, and alpha-(methylamino)-isobutyric acid appear to occur by the same population of transport-mediating sites. Both K(m) and V(max) of the Na(+)-sensitive uptake of these three amino acids change with changes in the concentration of Na(+), an effect which is shown to have a theoretical basis. A similarity in the values of Vmax for ten amino acids entering principally by the Na(+)-sensitive agency indicates that differences in their K(m) values probably measure differences in their affinities for that transport-mediating system.

Aminoisobutyric Acids↗

PubMed1983

Inhibition of amino acid transport by cis-diamminedichloroplatinum(II) derivatives in L1210 murine leukemia cells.

The uptake of cis-diamminedichloroplatinum(II) (cisplatin) has been studied in the L1210 murine lymphoid leukemia cell line. Labeled cisplatin and its aquated derivatives were resolved by high-performance liquid chromatography on a strong cationic exchange column. After 10 min of incubation of cisplatin with the cells, the major portion of the non-protein-bound platinum was in the form of cisplatin. However, a portion of this platinum was converted with time to a derivative which coeluted with the monoaquo derivative of cisplatin. With the appearance of this derivative, there was a concomitant inhibition of sodium-dependent amino acid transport as measured by the uptake of aminoisobutyric acid and methionine. Furthermore, the exposure of L1210 cells to a preparation of predominantly aquated product(s) of cisplatin inhibited amino acid uptake following a brief (2-min) incubation, whereas measurable inhibition of amino acid uptake by cisplatin required a longer preincubation period. This inhibition of aminoisobutyric acid and methionine was dependent on the concentration of platinum. Aminoisobutyric acid and methionine were shown to be concentrated in L1210 cells in the presence of sodium ions, and competition experiments suggest similar uptake systems. Since L1210 cells are methionine-auxotrophic leukemic cells, inhibition of essential amino acid transport by cisplatin may be a mechanism of cytotoxic action.

Aminoisobutyric Acids↗

PubMed1983

Increased blood-brain transfer in a rabbit model of acute liver failure.

The blood-to-brain transfer of [14C]alpha-aminoisobutyric acid was investigated by quantitative autoradiography in normal rabbits and rabbits with acute liver failure induced by the selective hepatotoxin galactosamine. The blood-to-brain transfer of alpha-aminoisobutyric acid was similar in control animals and animals 2 and 7 h after galactosamine injections, but was increased five- to tenfold in certain gray-matter areas of the brain in animals 11 and 18 h after galactosamine treatment. No detectable differences in white-matter uptake of [14C]alpha-aminoisobutyric acid were found between the control and treated groups. The increase in alpha-aminoisobutyric acid transfer within the gray-matter areas suggested that a general or nonspecific increase in brain capillary permeability occurred in these areas. No clinical signs of early hepatic encephalopathy were observed in the treated rabbits, except for 1 animal from the 18-h postgalactosamine group. Thus, enhanced blood-brain transfer of alpha-aminoisobutyric acid preceded the development of overt hepatic encephalopathy. The distribution of radioactivity after the intravenous administration of [14C]galactosamine showed that virtually none of the hepatotoxin localized in the brain, suggesting that the drug itself does not have a direct effect upon the blood-brain barrier or the brain. The increased uptake of alpha-aminoisobutyric acid at 11 and 18 h implies that the transfer of other solutes would also be enhanced, that central nervous system homeostasis would be compromised, and that the resulting changes in brain fluid composition could contribute to or cause hepatic encephalopathy.

Aminoisobutyric Acids↗

PubMed1972

Transport of amino acids into the oestrogen-primed uterus. Enchancement of the uptake by a preliminary incubation.

1. Preincubation of the immature rat uterus under physiological conditions was found to increase its subsequent ability to transport alpha-aminoisobutyric acid, l-proline, l-alanine and 1-aminocyclopentanecarboxylic acid. Uptakes of l-valine, l-phenylalanine and l-leucine were not affected. With alpha-aminoisobutyric acid, a doubling of the uptake could be obtained after a 3-5h preincubation period. Uteri from oestradiol-primed rats gave increases similar to those found in tissues from untreated animals. In both cases the preincubation increased the V(max.) of alpha-aminoisobutyric acid uptake but did not affect the K(m). 2. The conditions during the preincubation period determined the increase in subsequent uptake of alpha-aminoisobutyric acid. No increase in uptake was found if the preincubation was carried out at 1 degrees C, in the presence of cyanide or dinitrophenol, under anaerobiosis or with a concentration of puromycin that depressed incorporation of l-leucine into protein by 95%. The puromycin was also shown to prevent the increase in V(max.) normally found after the preincubation period. In addition, no increase was found if Na(+) was omitted from the preincubation medium. Other inorganic ions had smaller effects. 3. The uptake of alpha-aminoisobutyric acid by uteri before and after a preincubation period showed the same general patterns of sensitivity to competitive inhibitors, K(+), pH, temperature and 2,4-dinitrophenol. 4. The results suggest that the preincubation leads to an increase in a protein component of the ;A system' for amino acid transport in the uterus, and that metabolic energy is required for the reactions involved.

Alanine↗

PubMed1991

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.

Adrenal Medulla↗