Effects of 8-N,N-diethylamino-octyl-3,4,5-trimethoxybenzoate (TMB-8) HCL and verapamil on the metabolism of free fatty acid by hepatocytes

Olubadewo, Joseph O.; Cook, George A.; Heimberg, Murray

doi:10.1016/0006-2952(88)90007-x

Cited by 7 publications

(3 citation statements)

References 38 publications

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“…Results obtained with TMB-8 must also be interpreted with caution, even in cells exhibiting selective blockage of intracellular Ca2' release. In addition to the effects on choline transport and phospholipid metabolism described here, other Ca2+-independent effects of TMB-8 have also been reported for oxidative metabolism [9], ketogenesis [10] and superoxide production [8]. The mechanism of action is not known in these instances, and altered phospholipid metabolism may underlie some of the effects described.…”

Section: Measurement Of [3h]choline Incorporation Into Water-solublementioning

confidence: 55%

“…Phorbol ester activation of superoxide production in human polymorphonuclear leucocytes is also inhibited by TMB-8 by a mechanism that neither affects intracellular Ca2+ nor involves direct inhibition of protein kinase C [8]. TMB-8 may also interfere with oxidative metabolism [9], and is antiketogenic by inhibition of mitochondrial carnitine palmitoyltransferase [10]. At high concentrations [0.5-1 mM), TMB-8 is cytotoxic [6], decreases intracellular ATP [11], and disrupts membrane structure, causing leakage of cytoplasmic constituents [12].…”

Section: Introductionmentioning

confidence: 99%

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Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

Palmer

Byers

Spence

et al. 1992

Biochemical Journal

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TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.

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Section: Measurement Of [3h]choline Incorporation Into Water-solublementioning

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

Palmer

Byers

Spence

et al. 1992

Biochemical Journal

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“…In experiments with cultured hepatocytes verapamil inhibits in a concentration-dependent manner the secretion of verylow-density iipoproteins (VLDL) triglycerides (TG) without affecting the TG synthesis (Nossen et al 1985;Rustan et al 1987;Olubadewo et al 1988). Rustan et al (1987) concluded from their electron microscopic studies that the verapamil-induced inhibition of the VLDL secretion is primarily caused by an affection of the Golgi complex whose cisternal stacks revealed a strong swelling.…”

Section: Introductionmentioning

confidence: 98%

Biochemical and ultrastructural studies on the effect of verapamil on formation and secretion of lipoproteins in rat hepatocyte suspensions

et al. 1990

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The effect of the calcium channel blocker verapamil on structure, formation and secretion of very-low-density lipoproteins (VLDL) from rat hepatocytes in suspension was examined. After 30 min incubation at a verapamil dose of 200 microM neither free fatty acid (FFA) uptake nor triglyceride (TG) and phospholipid (PL) secretion into the incubation medium were significantly changed. After 90 min incubation the TG secretion was inhibited by about 60%, whereas the PL output was only insignificantly lowered, indicating the secretion of abnormally composed lipoprotein particles. Morphologically, after 30 min incubation the hepatocytes had lost their microvillous border and exhibited a 2-3-fold increase in volume density and average size of the lysosomes. In the Golgi-containing regions an accumulation of smooth-surfaced microvesicles was regularly evident. The configuration of the Golgi complexes was normal. After 90 min incubation the lysosomes showed a further significant elevation in volume and size. The Golgi complexes exhibited only minor changes, but their content in VLDL particles was reduced per microns 2 Golgi complex by about 75%. Commonly, the VLDL were larger and more heterogenous in size. The diameter of those VLDL secreted into the incubation medium ranged from 31 to 84 nm, thus surpassing the control values by 2-3 times. The secretion of large-sized VLDL was regularly associated with the intracytoplasmic appearance of dilated smooth-surfaced vesicles filled with size-modified VLDL. These vesicles were concentrated within Golgi-containing areas from where they were widely dispersed towards the cell periphery.(ABSTRACT TRUNCATED AT 250 WORDS)

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Effects of inositol trisphosphate on calcium mobilization in bone cells

et al. 1991

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The effect of inositol 1,4,5 trisphosphate (IP3) on calcium mobilization was studied in human osteosarcoma lines, Saos-2 and G292, as well as isolated rat osteoblastic and osteoclastic cells. Cells were permeabilized with saponin and calcium mobilization was studied with the fluorescent dye, fura-2 in a recording spectrofluorometer. IP3 (10 microM) increased calcium release in all cell types studied. The effect was dependent on ATP and occurred in the presence of mitochondrial inhibitors. The effect was not seen with inositol 1-phosphate (IP) or inositol 1,4-diphosphate (IP2). Inositol 1,3,4,5 tetrakisphosphate (IP4) appeared to elicit a decrease in the calcium released. Depletion of the intracellular pool with the calcium ionophore, ionomycin, as well as incubation with the inhibitor of intracellular calcium mobilization, TMB-8, obliterated the IP3 effect. The results are consistent with the hypothesis that increases in IP3 can cause a rapid elevation of bone cell cytosolic calcium.

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Effects of 8-N,N-diethylamino-octyl-3,4,5-trimethoxybenzoate (TMB-8) HCL and verapamil on the metabolism of free fatty acid by hepatocytes

Cited by 7 publications

References 38 publications

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

Biochemical and ultrastructural studies on the effect of verapamil on formation and secretion of lipoproteins in rat hepatocyte suspensions

Effects of inositol trisphosphate on calcium mobilization in bone cells

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