Mechanism of inhibitory action of TMB-8 [8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate] on aldosterone secretion in adrenal glomerulosa cells

Abstract

The mechanism of 8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) action was evaluated in isolated adrenal glomerulosa cells. TMB-8 inhibits both angiotensin II- and K+-stimulated aldosterone secretion in a dose-dependent manner. The ID50 for angiotensin II- and K+-stimulated aldosterone secretion is 46 and 28 microM, respectively. In spite of the fact that 100 microM-TMB-8 inhibits angiotensin II-stimulated aldosterone secretion almost completely, TMB-8 (100 microM) does not inhibit angiotensin II-induced 45Ca2+ efflux from prelabelled cells nor does it affect inositol 1,4,5-trisphosphate-induced calcium release from non-mitochondrial pool(s) in saponin-permeabilized cells. TMB-8 has no inhibitory effect on A23187-induced aldosterone secretion, but 12-O-tetradecanoylphorbol 13-acetate-induced aldosterone secretion is completely abolished. TMB-8 effectively inhibits both angiotensin II- and K+-induced increases in calcium influx but has no effect on A23187-induced calcium influx. TMB-8 inhibits the activity of protein kinase C dose-dependently. These results indicate that TMB-8 inhibits aldosterone secretion without inhibiting mobilization of calcium from an intracellular pool. The inhibitory effect of TMB-8 is due largely to an inhibition of plasma membrane calcium influx, but this drug also inhibits the activity of protein kinase C directly.

Irsogladine Inhibits Ionomycin-Induced Decrease in Intercellular Communication in Cultured Rabbit Gastric Epithelial Cells

“…However, it should be noted that TMB-8 may also act on protein kinase C and plasma membrane Ca 21 influx (23). In this experiment, TMB-8 also inhibited both the elevation of [Ca 2+]; and the decrease in intercellular communication induced by ionomycin.…”

The effects of TMB-8 on the shape changes of vascular endothelial cells resulting from exposure to various inflammatory agents

“…This enzyme is calcium dependent. It has since been demonstrated that TMB-8 (100 ~tM) inhibits protein kinase C in isolated adrenal glomerulosa cells, but does not inhibit mobilisation of calcium from an intracellular pool [15]. It has also been suggested that TMB-8 may act by antagonising some of the actions of intracellular calcium rather than its release; for example, calcium-dependent mechanisms associated with the activation of phospholipases [16,17] and the responses of rat isolated atria to conditions of simulated ischaemia which almost certainly involve intracellular calcium ions [18].…”

Downregulation of cell-to-cell communication by the viralsrc gene is blocked by TMB-8 and recovery of communication is blocked by vanadate

“…Continuity of the diacylglycerol pathway requires mobilization of Ca 2+ to the locale of protein kinase C; translocation of this enzyme from the cytoplasm to the plasma membrane requires 2-5 x 10 -7 M Ca 2+ (Wolf et al, 1985) and its activation requires (besides diacylglycerol) >10 -6 Ca 2+ (Kishimoto et al, 1980), concentrations higher than that normally in the cytosol (Baker, 1976). Since TMB-8 blocks Ca 2+ mobilization to cytosoi (Mix et al,, 1984;Sawamura, 1985; but see also Kojima et al, 1985), we are immediately drawn to protein kinase C as a possible site where such a blockade might critically in- terfere with the pathway. Alternatively or additionally, the blockade may occur further down the pathway at a critical Ca2+-dependent step closer to the channel or at the channel itself, as proposed and discussed in more detail elsewhere (Yada et al, 1985).…”

“…That inhibition requires relatively high TMB-8 concentrations. A 50% inhibition, in the presence of 12.5 /~g/ml phospholipid (and 150 /~M Ca2+), requires between 100 to 250 p~M TMB-8 in one in vitro system (Kojima et al, 1985) and 300 ~M in another (Sawamura, 1985;Y. Nishizuka, personal communication), and in the presence of higher lipid concentrations (160/~g/ml) even 400/~M TMB-8 produced only a <10% inhibition (Sawamura, 1985).…”

“…We asked whether the downregulation of junctional communication by src could be blocked by 8-N,N-(diethylamino)octyi-3,4,5-trimethoxybenzoate (TMB-8), an inhibitor of intracellular Ca 2+ mobilization (Chiou & Malagodi, 1975;Mix, Dinerstein & Villereal, 1984;Sawamura, 1985) and of protein kinase C (Kojima, Kojima & Rasmussen, 1985;Sawamura, 1985). Protein kinase C is the key enzyme in the diacylglycerol pathway and Ca 2+ is known to play a crucial role in its activation; the free ionized Ca 2+ concentration in the cytoplasm must rise to 10 -6 M for activation of protein kinase C (Kishimoto et al, 1980).…”