phorbol and 1-oleoyl-2-acetylglycerol

1. The effects of 1-oleoyl-2-acetyl-sn-glycerol (OAG), phorbol 12-myristate 13-acetate (PMA), 4-alpha-phorbol and muscarine on B-neurones from bull-frog sympathetic ganglion were studied by means of whole-cell patch-clamp recording. With the exception of 4-alpha-phorbol, all of these agonists reduced the steady-state outward current recorded at -30 mV as a result of suppression of a voltage-dependent, non-inactivating K(+)-current, the M-current, (IM). 2. Of the cells tested, 34% displayed bona fide responses to OAG (20 microM). The chance of recording a response was not decreased when the protein kinase inhibitor, 1-(5-isoquinolinylsulphonyl)-2-methyl-piperazine (H-7; 50 or 75 microM) was included simultaneously in the extracellular solution and in the pipette solution. 3. The presence of 50 microM H-7 on both sides of the membrane or 500 nM staurosporine in the pipette solution did not prevent responses to brief (1-2 min) or prolonged (> 20 min) applications of PMA. 4. Brief (1-2 min) extracellular application of H-7 (300 microM) suppressed IM by about 29%. 5. The most likely explanation of these data is that PMA and OAG modulate IM via a mechanism that is independent of protein kinase C (PKC). The availability of such a mechanism poses new questions as to the mechanism of muscarine-induced IM suppression.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Diglycerides; Ganglia, Sympathetic; Isoquinolines; Muscarinic Agonists; Neurons; Patch-Clamp Techniques; Phorbol Esters; Phorbols; Piperazines; Protein Kinase C; Protein Kinase Inhibitors; Rana catesbeiana; Receptors, Muscarinic; Tetradecanoylphorbol Acetate

Using a paced Lagendorff-perfused rabbit heart paradigm, we investigated the role of protein kinase C (PKC) in the development of ventricular fibrillation (VF) in hearts subjected to hypoxia (12 min) and re-oxygenation (40 min). We studied the effect of putative activators and inhibitors of PKC on the incidence of VF. Hearts exposed to 4 beta-phorbol,12,13-dibutyrate (PDBu), isophorbol or the membrane permeant diacylglycerol analog, 1-oleoyl-2-acetyl-rac-glycerol (OAG), during the prehypoxic phase had an increased incidence of VF during the hypoxic and reoxygenation periods. The incidence of VF was 90%, 83% and 75% in hearts exposed to PDBu, isophorbol and OAG, respectively (P < 0.05 vs control). Perfusion of hearts with PDBu was associated with a significant increase in the membrane fraction of cardiac PKC activity. In the presence of the inactive phorbol ester 4 alpha-phorbol didecanoate, the incidence of VF was 17% (P > 0.05 vs control). PKC activators were profibrillatory at concentrations that did not affect cardiac function: neither left ventricular developed pressure nor coronary perfusion pressure were affected. The effect of PDBu was antagonized by staurosporine: the incidence of VF was 17% in PDBu+staurosporine treated hearts (P < 0.05 vs control). To further study the profibrillatory effect of PDBu, hearts were exposed to PDBu in the presence of the ATP-dependent potassium channel antagonist glibenclamide. The latter prevented PDBu-induced VF. The results show that under the conditions employed, PDBu-induced activation of PKC induces redistribution of PKC activity and is associated with the development of VF.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Alkaloids; Animals; Diglycerides; Glyburide; Guanidines; Isoquinolines; Perfusion; Phorbol 12,13-Dibutyrate; Phorbol Esters; Phorbols; Pinacidil; Piperazines; Protein Kinase C; Rabbits; Staurosporine; Ventricular Fibrillation

Recent findings have demonstrated that prostanoid-generated calcium fluxes can trigger myoblast fusion and suggest inositol phospholipid turnover as part of the fusion mechanism. Here we demonstrate that a block imposed on myoblast fusion by antagonists of prostanoid biosynthesis can be overcome by either the membrane-permeable diacylglycerol, 1-oleoyl-2-acetyl-sn-glycerol (OAG), or 12-O-tetradecanoylphorbol 13-acetate (TPA). Both phorbol and the membrane-impermeable dioleoylglycerol were ineffective. These results implicate protein kinase C activation in prostaglandin E1-mediated myoblast fusion and add weight to the contention that inositol turnover is involved in the regulation of myoblast fusion.

Topics: Alprostadil; Animals; Cell Fusion; Cells, Cultured; Chick Embryo; Diglycerides; DNA; Enzyme Activation; Indomethacin; Muscles; Myosins; Phorbols; Protein Kinase C; Tetradecanoylphorbol Acetate

Miniature endplate potentials and nerve-evoked endplate potentials were studied in a phrenic nerve-diaphragm preparation of the mouse. A phorbol ester, phorbol-12 beta, 13 alpha-dibutyrate, and a diacylglycerol, 1-oleyl-2-acetyl-sn-glycerol, both increased the frequency of miniature endplate potentials. The effect of the phorbol ester on the frequency was still significant when the preparation was incubated in a calcium-deficient solution. The phorbol ester, but not the diacylglycerol, caused a significant increase in the amplitude of the miniature potentials. The phorbol ester also increased the amplitude of the endplate potentials in the presence of (+)-tubocurarine. The mechanisms of action of phorbol ester and diacylglycerol are discussed in relation to the control of acetylcholine release and action at the neuromuscular junction.

Topics: Animals; Benzylamines; Calcium; Diaphragm; Diglycerides; Electric Stimulation; Glycerides; In Vitro Techniques; Magnesium; Membrane Potentials; Mice; Motor Endplate; Neuromuscular Junction; Pargyline; Phorbol 12,13-Dibutyrate; Phorbol Esters; Phorbols; Phrenic Nerve; Stereoisomerism; Tubocurarine

The role of C-kinase in the triggering of the neutrophil oxidase by two stimuli (latex beads and the chemotactic peptide fMet-Leu-Phe), representative of endocytotic and exocytotic routes of activation, were investigated by using experimental agents that activate, or inhibit C-kinase, in intact cells. The activation by the phagocytotic stimulus latex beads was mimicked by C-kinase activators giving the same characteristic lag (20-30s), followed by a constant oxygen consumption rate with the same maximum rate and affinity for oxygen (Km approx. 13 microM), competed with activation by PMA (4 beta-phorbol 12-myristate 13-acetate) in a simple common-target manner, and was inhibited by retinal, an inhibitor shown to inhibit activation by PMA. In contrast, activation by chemotactic peptide was not mimicked by C-kinase activation alone, chemotactic peptide inducing biphasic oxygen consumption with a Km for oxygen of the second prolonged phase of 3.9 microM, did not compete with activation by PMA, and was not inhibited by retinal. However, PMA and retinal produced slight enhancements of activation by chemotactic peptide and production of monophasic oxygen consumption. It was concluded that C-kinase activation plays a simple central transducing role in activation of the oxidase by latex beads, but that its role in activation by chemotactic peptide is a part of a more complex set of interactions that involve other Ca2+-activated and non-Ca2+-activated processes.

Topics: Animals; Diglycerides; Diterpenes; Enzyme Activation; In Vitro Techniques; Latex; N-Formylmethionine Leucyl-Phenylalanine; NADH, NADPH Oxidoreductases; Neutrophils; Phorbols; Protein Kinase C; Rats; Terpenes; Tetradecanoylphorbol Acetate