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R Seifert

Publications and source records attributed to R Seifert.

At least 19 recordsLinked to original sources
PubMed1995

Synthetic lipopeptides activate nucleoside diphosphate kinase in HL-60 membranes.

We have put forward the hypothesis that lipopeptides (LPs) activate GTP hydrolysis by Gi-proteins in HL-60 membranes via activation of nucleoside diphosphate kinase (NDPK) as does mastoparan (MP). Therefore, we compared the effects of LPs and MP on NDPK- and GTPase activation in HL-60 membranes. In native membranes, LPs effectively activated GTP hydrolysis and moderately activated GTP formation. In solubilized membranes, the effect of LPs on GTP formation was enhanced whereas the one on GTP hydrolysis was abolished. The NDPK substrate GDP enhanced the relative stimulatory effect of LPs and MP on GTP hydrolysis in HL-60 membranes in the absence of a NTP-regenerating system. A NTP-regenerating system abrogated the potentiating effect of GDP on MP-action, whereas the effect on LP-stimulated GTP-hydrolysis was enhanced. Our data show that LPs activate NDPK in HL-60 membranes and that this activation may account for their G-protein-stimulatory activity. Membrane solubilization may impair the transfer of GTP from NDPK to Gi-protein alpha-subunits and subsequent GTP hydrolysis, whereas GTP formation remains intact, augmenting the effect of LPs on the kinase. Finally, LP- and MP-induced NDPK activation may involve different pools of GDP.

Amino Acid Sequence↗
PubMed1995

Histamine receptor-dependent and/or -independent activation of guanine nucleotide-binding proteins by histamine and 2-substituted histamine derivatives in human leukemia (HL-60) and human erythroleukemia (HEL) cells.

In dibutyryl cAMP-differentiated human leukemia (HL-60) cells, the potent histamine H1-receptor agonist, 2-(3-chlorophenyl)histamine, activates pertussis toxin (PTX)-sensitive guanine nucleotide-binding proteins (G-proteins) of the Gi-subfamily by a mechanism which is independent of known histamine receptor subtypes (Seifert et al. Mol Pharmacol 45: 578-586, 1994). In order to learn more about this G-protein activation, we studied the effects of histamine and various 2-substituted histamine derivatives in various cell types and on purified G-proteins. In HL-60 cells, histamine and 2-methylhistamine increased cytosolic Ca2+ concentration ([Ca2+]i) in a clemastine-sensitive manner. Phenyl- and thienyl-substituted histamines increased [Ca2+]i as well, but their effects were not inhibited by histamine receptor antagonists. 2-Substituted histamines activated high-affinity GTPase in HL-60 cell membranes in a PTX-sensitive manner, with the lipophilicity of substances increasing their effectiveness. Although HEL cells do not possess histamine receptors mediating rises in [Ca2+]i, 2-(3-bromophenyl)histamine increased [Ca2+]i in a PTX-sensitive manner. It also increased GTP hydrolysis by Gi-proteins in HEL cell membranes. All these stimulatory effects of 2-substituted histamine derivatives were seen at concentrations higher than those required for activation of H1-receptors. In various other cell types and membrane systems, 2-substituted histamine derivatives showed no or only weak stimulatory effects on G-proteins. 2-Substituted histamine derivatives activated GTP hydrolysis by purified bovine brain Gi/Go-proteins and by pure Gi2 (the major PTX-sensitive G-protein in HL-60 and HEL cells). Our data suggest the following: (1) histamine and 2-methylhistamine act as H1-receptor agonists in HL-60 cells; (2) incorporation of bulky and lipophilic groups results in loss of H1-agonistic activity of 2-substituted histamine derivatives in HL-60 cells but causes a receptor-independent G-protein-stimulatory activity; (3) the effects of 2-substituted histamine derivatives on G-proteins are cell-type specific.

Animals↗
PubMed1995

Differential activation of Gi and Gs proteins by E- and I-type prostaglandins in membranes from the human erythroleukaemia cell line, HEL.

The group of prostaglandin (PG) E2- and prostacyclin receptors consists of different subtypes, which exhibit different affinities for prostaglandins and synthetic analogues. PGE2 activities the E-type PG receptor subtypes EP1, EP2 and EP3, whereas the PGE2 analogue, sulprostone, binds only to the EP1 and EP3 receptor subtypes. The stable PGI2 analogues, iloprost and cicaprost, both activate the PGI2 receptor (IP) and iloprost, additionally, bind to the EP1 subtype. Using these subtype-selective PG receptor agonists, we studied the interaction of PG receptor subtypes with Gs and Gi-type heterotrimeric guanine nucleotide-binding proteins (G proteins) in membranes from the human erythroleukaemia cell line, HEL. Sulprostone stimulated high-affinity GTPase in HEL membranes in a pertussis toxin (PTX)-sensitive manner. In contrast, the stimulations induced by PGE2, iloprost and cicaprost were only partially inhibited by PTX. PGE2, sulprostone, iloprost and cicaprost stimulated cholera toxin-catalysed ADP-ribosylation as well as labelling with GTP azidoanilide of membrane proteins comigrating with immunologically identified Gi protein alpha subunits. Furthermore, PGE2, iloprost and cicaprost enhanced GTP azidoanilide-labelling of Gs protein alpha subunits, whereas sulprostone did not. We suggest that in HEL cells (1) EP1 and EP3 receptor subtypes activate G1 proteins, that (2) the EP2 receptor subtype activates Gs proteins and that (3) the IP receptor activates both Gi and Gs proteins.

Cell Membrane↗
PubMed1995

Alpha 2A-adrenoceptors mediate activation of non-selective cation channels via Gi-proteins in human erythroleukaemia (HEL) cells. No evidence for a functional role of imidazoline receptors in modulating calcium.

Human erythroleukaemia (HEL) cells were investigated to characterize their alpha 2-adrenoceptor and imidazoline receptor sites. Membranes from HEL cells bound [3H]2-(2-methoxy-1, 4-benzodioxan-2yl)-2-imidazoline ([3H]RX821002) in a saturable and specific manner with a KD of 0.64 +/- 0.07 nM and a Bmax of 126 +/- 4 fmol/mg protein. [3H]RX821002 was displaced from HEL membranes by adrenergic drugs with the order of potency being yohimbine approximately oxymetazoline >> prazosin = 2-[2-[4-(o-methoxyphenyl)piperazin-1-yl]ethyl]-4,4-dimethyl- 1,3(2H,4H)-isochinolindione HCl (ARC 239), consistent with this site being an alpha 2A-adrenoceptor. HEL membranes also bound [3H]idazoxan in the presence of adrenaline to block alpha 2-adrenoceptors. This binding was saturable and specific with a KD of 3.5 +/- 1.0 nM and a Bmax of 31 +/- 6 fmol/mg protein. Adrenergic drugs from both the phenylethylamine and imidazoline classes increased high-affinity GTPase activity, an index of activation of regulatory heterotrimeric guanine-nucleotide binding proteins (G-proteins), and produced increases in cytosolic free calcium concentration ([Ca2+]i). The effects of these agonists in both systems were abolished by pertussis toxin pretreatment, and oxymetazoline and clonidine were antagonists. The potency of adrenergic drugs to inhibit 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14304)-induced increases in [Ca2+]i was yohimbine approximately oxymetazoline >> ARC 239, consistent with the binding data and an action at alpha 2A-adrenoceptors. No evidence was found for a role of imidazoline receptors in stimulating G-proteins or modulating [Ca2+]i. The adrenergic agonist-induced increases in [Ca2+]i were due to both release of Ca2+ from intracellular stores and entry of extracellular Ca2+. Ca2+ entry was blocked by 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenylethyl)-1H- imidazole hydrochloride (SKF 96365), but not by nitrendipine. Adrenaline also stimulated Mn2+ entry in HEL cells. Taken together, these results suggest that HEL cells have alpha 2A-adrenoceptors that activate non-selective cation channels via pertussis toxin-sensitive G-proteins, i.e. Gi-proteins.

Binding, Competitive↗
PubMed1995

Blood vessel formation in the avian limb bud involves angioblastic and angiotrophic growth.

The vasculature of the avian limb bud takes its origin from the intersomitic vessels as can be shown by ink perfusion of the embryo. While the primitive vessels form a central network in the early limb bud, an area of about 100 microns in width from the ectoderm inward remains free from lumenized vessels. However, this subectodermal avascular zone contains isolated angioblasts, which can be demonstrated by confocal laser scanning microscopy in connection with QH-1-staining. QH-1-positive cells from the avascular zone are capable of giving rise to endothelial cells when grafted ectopically into a "permissive" environment such as the dorso-lateral paraxial mesoderm. Several grafting sites are compared regarding their permissiveness for capillary formation. In order to investigate the origin of the QH-1-positive angioblasts we carried out injections of DiI-Ac-LDL, which is specifically taken up by endothelial cells and macrophages, and found the lumenized vessels and a few isolated cells in the peripheral limb mesoderm stained. In double-labelling studies combining DiI-Ac-LDL and QH-1, it can be shown that there exists a pool of isolated angioblasts that are only QH-1-positive, but have not incorporated DiI-Ac-LDL. In contrast to the lumenized vessels in the core of the limb bud, we found that angioblasts in the avascular zone do not proliferate, as shown by proliferation studies applying the BrdU-method to semithin sections in connection with QH-1-labelled parallel sections. We conclude that the vascularization of the avian limb bud is achieved by a combination of angiotrophic growth (sprouting of vessels) and angioblastic growth (recruitment of angioblasts from the limb mesoderm.

Animals↗
PubMed1995

Cationic-amphiphilic arpromidine-derived guanidines and a histamine trifluoromethyl-toluidide derivative may activate pertussis toxin-sensitive G-proteins by a receptor-independent mechanism.

Formyl peptides activate superoxide anion (O2-) formation in human neutrophils and in HL-60 cells via pertussis toxin (PTX)-sensitive guanine nucleotide-binding proteins (G-proteins), and histamine (HA) mediates inhibition of O2- formation via H2-receptors. We have studied the effects of lipophilic arpromidine-derived guanidines, which are potent, full H2-receptor agonists in the guinea pig atrium, on O2- formation and on activation of G-proteins in HL-60 membranes and on purified G-proteins. We have also studied the effects of a HA trifluoromethyl-toluidide derivative (HTMT), a cationic-amphiphilic HA derivative which activates O2- formation in HL-60 cells through a mechanism which is independent of known HA receptor subtypes, on G-protein activation. Guanidines, at concentrations, up to 30 mumol/l inhibited and, at concentrations above 30 mumol/l, enhanced formyl peptide-induce O2- formation in neutrophils. In HL-60 cells, guanidines per se activated O2- formation. The stimulatory effects of guanidines on O2- formation were not inhibited by H1- or H2-receptor antagonists. In HL-60 membranes, guanidines and HTMT, activated high-affinity GTPase in a PTX-sensitive manner. These substances also increased GTP hydrolysis effected by transducin and Gi/G(o)-proteins. Our data suggest that lipophilic guanidines and HTMT may act as receptor-independent activators of PTX-sensitive G-proteins, resulting in stimulation of O2- formation.

Biotransformation↗
PubMed1995

Profoundly different calcium permeation and blockage determine the specific function of distinct cyclic nucleotide-gated channels.

Sensory transduction in vertebrate photoreceptors and olfactory sensory neurons is mediated by cyclic nucleotide-gated (CNG) channels that conduct mono- and divalent cations. Ca2+ entering the cell through CNG channels intimately controls signaling pathways by regulating several key enzymes. Cloned CNG channels from photoreceptors and olfactory sensory neurons profoundly differ in their relative Ca2+ permeability, their blockage by external divalent cations, and the fraction of current carried by Ca2+. In particular, CNG channels from cone photoreceptors conduct significantly more Ca2+ than those from rod photoreceptors. Furthermore, the current through the olfactory CNG channel is entirely carried by Ca2+ at approximately 3 mM extracellular Ca2+. These results suggest that a major function of CNG channels is to provide a pathway for Ca2+ entry.

Animals↗
PubMed1995

A 240 kDa protein represents the complete beta subunit of the cyclic nucleotide-gated channel from rod photoreceptor.

The cyclic nucleotide-gated channel from rod photoreceptors is composed of two distinct subunits (alpha and beta). The properties of the alpha subunit, which can form functional channels by itself, are modified by coexpression with a homologous polypeptide, designated the beta subunit. However, the alpha subunit from rod photoreceptor membranes copurifies with a 240 kDa protein that is significantly larger than this putative beta subunit. We now demonstrate by peptide sequencing and by cloning and functional expression of cDNA that the 240 kDa protein represents the complete beta subunit with an unusual bipartite structure. The N-terminal part is essentially identical to a glutamic acid-rich protein (GARP), whereas the C-terminal part is highly homologous to the previously cloned human "beta subunit." Expression of the complete beta subunit in HEK 293 cells results in a polypeptide with the same apparent molecular weight as the 240 kDa protein of the native rod channel. Coexpression of the alpha subunit with the full-length beta subunit yields hetero-oligomeric channels with properties characteristic of the native channel.

Amino Acid Sequence↗
PubMed1995

[Quantitative EEG, basic disorders and smoking in etiopathogenetically different groups of paranoid-hallucinatory psychoses--an exploratory study].

We performed an exploratory study of quantitative EEG in aetiopathogenetically different paranoid-hallucinatory psychoses divided into the following groups: a) patients with familial psychoses (n = 12), b) patients with neuropsychological deficits (n = 16), c) patients with alcohol and drug abuse (n = 22) and d) patients with so-called sporadic psychoses (n = 12). We found a significant reduction of relative alpha power in the group with neuropsychological deficits. In the group with familial psychosis there was a significant reduction of absolute delta power and a significant increase of relative beta power and dominant beta frequency, especially for the frontal leads. Patients with drug abuse showed a reduction of absolute beta power and an increase of absolute and relative theta power. The group with sporadic psychosis showed a significant slowing of the dominant beta frequency and a significant increase of the absolute power of fast alpha rhythms. The group with sporadic psychoses showed lowered scores for the paranoid-hallucinatory basic symptom factor. The group with neuropsychological deficits showed the most visceral-somatoform basic symptoms, the highest nicotine consumption, increased dyskinesias and more perinatal complications. This group also showed the highest level of neuroleptic and antiparkinson medication. All in all, the group with neuropsychological deficits showed a complex interaction of somatic-exogenic and medical-iatrogenic factors. Furthermore, there was a significant positive correlation between paranoid-hallucinatory basic symptoms and nicotine abuse and high frequency beta waves.

Adult↗
PubMed1995

The class III antiarrhythmic drug amiodarone directly activates pertussis toxin-sensitive G proteins.

The class III antiarrhythmic drugs amiodarone and bretylium tosylate are cationic/amphiphilic, and various substances with these physico-chemical properties are known to directly activate heterotrimeric regulatory G proteins. We asked the question of whether class III antiarrhythmic drugs are also direct G protein activators, using HL-60 leukemic cells and purified bovine brain G proteins as model systems. In HL-60 cell membranes, aminodarone increased high affinity GTP hydrolysis with an EC50 of 7.5 microM. The stimulatory effect of amiodarone on GTP hydrolysis was inhibited by pertussis toxin. Amiodarone stimulated binding of guanosine-5'-O-(3-thio)triphosphate to, and incorporation of GTP azidoanilide into, Gi protein alpha subunits in HL-60 membranes. The drug increased the cytosolic Ca2+ concentration in HL-60 cells in the presence but not in the absence of extracellular Ca2+. Amiodarone-induced increases in the cytosolic Ca2+ concentration were reduced by pertussis toxin and by a blocker of non-selective cation channels, SK&F 96365. Amiodarone activated the GTPase of reconstituted Gi/G(o) proteins and G12 with EC50 values of 20 microM and 50 microM, respectively. Bretylium tosylate did not increase GTP hydrolysis in HL-60 membranes or with Gi/G(o) proteins. Our data suggest that amiodarone but not bretylium tosylate is a direct activator of Gi and G(o) proteins and that amiodarone activates nonselective cation channels in HL-60 cells via Gi proteins and independently of Ca2+ mobilization from intracellular stores. Future studies will have to test the hypothesis that direct G protein activation by amiodarone contributes to its toxic and/or therapeutic effects.

Amiodarone↗
PubMed1994

Differential activation of dibutyryl cAMP-differentiated HL-60 human leukemia cells by chemoattractants.

Dibutyryl cAMP-differentiated HL-60 human leukemia cells possess receptors for the chemoattractants N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), C5a and leukotriene B4 (LTB4). We compared the effects of these chemoattractants in HL-60 membranes and in intact HL-60 cells. fMLP, C5a and LTB4 stimulated GTP hydrolysis and guanosine 5'-O-[3-thio]triphosphate (GTP[gamma S]) binding in HL-60 membranes with similar effectiveness and in a pertussis toxin (PTX)-sensitive manner. They also stimulated photolabeling of the alpha-subunits of the guanine nucleotide-binding proteins (G-proteins), Gi2 and Gi3 with similar effectiveness. Chloride salts of monovalent cations differentially enhanced and inhibited chemoattractant-induced GTP hydrolyses. C5a was less effective than fMLP in enhancing cholera toxin-catalysed ADP-ribosylation of Gi alpha 2 and Gi alpha 3, and LTB4 was ineffective. fMLP was more effective than C5a and LTB4 in stimulating Ca2+ influx in HL-60 cells. C5a- and LTB4-induced rises in cytosolic Ca2+ concentration ([Ca2+]i) were PTX-sensitive, whereas the effect of fMLP was partially PTX-insensitive. LTB4-induced rises in [Ca2+]i were more sensitive towards homologous desensitization than those induced by C5a, and the effect of fMLP was resistant in this regard. C5a was considerably less effective than fMLP in activating superoxide anion formation and azurophilic granule release, and LTB4 was ineffective. Our data suggest that fMLP, C5a and LTB4 effectively activate the G-proteins, Gi2 and Gi3, in HL-60 cells and that fMLP may additionally activate PTX-insensitive G-proteins. fMLP, C5a and LTB4 are full, partial and incomplete secretagogues, respectively, and these differences may be due to differences in homologous receptor desensitization and qualitative Gi-protein activation.

Bucladesine↗
PubMed1994

Primary structure and functional expression of a Drosophila cyclic nucleotide-gated channel present in eyes and antennae.

Cyclic nucleotide-gated (CNG) ion channels serve as downstream targets of signalling pathways in vertebrate photoreceptors and olfactory sensory neurons. Whether CNG channels subserve similar functions in invertebrate photoreception and olfaction is unknown. We have cloned genomic DNA and cDNA encoding a cGMP-gated channel from Drosophila. The gene contains at least seven exons. Heterologous expression of cloned cDNA in both Xenopus oocytes and HEK 293 cells gives rise to functional ion channels. The Drosophila CNG channel is approximately 50-fold more sensitive to cGMP than to cAMP. The voltage dependence of blockage by divalent cations is different compared with the CNG channel of rod photoreceptors, and the Ca2+ permeability is much larger. The channel mRNA is expressed in antennae and the visual system of Drosophila. It is proposed that CNG channels are involved in transduction cascades of both invertebrate photoreceptors and olfactory sensillae.

Amino Acid Sequence↗
PubMed1994

Evidence that inhibition of phorbol ester-induced superoxide anion formation by cyclosporin A in phagocytes is not mediated by direct inhibition of protein kinase C.

Cyclosporin A (CsA) has been reported to inhibit phorbol myristate acetate (PMA)-induced superoxide anion (O2-) formation in human neutrophils and murine macrophages. We found that CsA inhibited O2- formation in HL-60 cells induced by PMA (30 nM) and phorbol dibutyrate (200 nM) with a half-maximal effect at 1 and 0.75 microM, respectively. One possible target of CsA action is protein kinase C (PKC) [EC 2.7.1.37] since phorbol esters activate this kinase. However, CsA did not inhibit PMA-mediated reduction of histamine-induced rises in cytosolic Ca2+ concentration in, and PMA-induced differentiation of, HL-60 cells and platelet aggregation. CsA did not reduce the activity of various recombinant c-PKC isoenzymes (alpha, beta 1 and gamma), n-PKC isoenzymes (delta and epsilon), an a-PKC isoenzyme (zeta) nor of PKC purified from rat brain in vitro. These data show that CsA inhibits phorbol ester-induced O2- formation in HL-60 cells but not other phorbol ester-mediated events and that inhibition by CsA of O2- formation cannot readily be attributed to direct PKC inhibition. We also show that CsA does not change the activity of nucleoside diphosphate kinase [EC 2.7.4.6] in HL-60 membranes nor the latter's physical properties.

Animals↗
PubMed1994

Maitotoxin activates cation channels distinct from the receptor-activated non-selective cation channels of HL-60 cells.

We investigated whether maitotoxin activates non-selective cation channels, as was recently proposed [Soergel, Yasumoto, Daly and Gusovsky (1992) Mol. Pharmacol. 41, 487-493]. Stimulation of dibutyryl cyclic AMP-differentiated HL-60 cells with the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP; 0.1 microM), the Ca(2+)-ATPase inhibitor thapsigargin (0.1 microM) or maitotoxin (25 ng/ml) resulted in an increase in cytoplasmic free calcium concentration ([Ca2+]i). Unlike fMLP and thapsigargin, maitotoxin produced no increase in [Ca2+]i in the absence of extracellular Ca2+. The increase in [Ca2+]i induced by fMLP was blocked by pretreatment with pertussis toxin (100 ng/ml for 24 h) but not that induced by maitotoxin. Similarly, the increase in [Ca2+]i produced by fMLP but not that produced by maitotoxin was inhibited by pretreatment with phorbol myristate acetate (100 ng/ml). Both fMLP- and maitotoxin-induced increases in [Ca2+]i were blocked by 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenylethyl)-1H-imid azole hydrochloride (SKF 96365) in a concentration-dependent manner. However, the maitotoxin-induced increase in [Ca2+]i was more sensitive to inhibition by SKF 96365 than the fMLP-induced increase. fMLP-induced increases in [Ca2+]i were blocked by cations with Gd3+ being more effective than Cd2+, whereas for maitotoxin Cd2+ was more effective than Gd3+. Both fMLP and thapsigargin stimulated quenching of Fura-2 fluorescence in the presence of extracellular Mn2+, whereas maitotoxin produced no Mn2+ quenching. Taken together these results suggest that maitotoxin does not stimulate the nonselective cation channel activated by fMLP, but instead activates Ca2+ influx by a different mechanism.

Bucladesine↗
PubMed1994

Lipophilic beta-adrenoceptor antagonists and local anesthetics are effective direct activators of G-proteins.

We studied the effects of various beta-adrenoceptor (beta AR) antagonists and local anesthetics (LAs), i.e. substances possessing one basic and one lipophilic domain each, on activation of regulatory heterotrimeric guanine nucleotide-binding proteins (G-proteins). In membranes of differentiated HL-60 cells, propranolol activated high-affinity GTP hydrolysis with a half-maximal effect at 0.19 mM and a maximum at 1 mM. There was a close correlation between the log Q values (logarithm of the octanol: water partition coefficient) of beta AR antagonists and the logarithm of their effectiveness at activating GTPase (EC 3.6.1.-) in HL-60 membranes. The lipophilic LA, tetracaine, was also an effective activator of GTPase in HL-60 membranes, whereas more hydrophilic LAs were less stimulatory (bupivacaine and lidocaine) or even inhibitory (procaine). Propranolol and tetracaine also stimulated binding of guanosine 5'-O-[3-thio]triphosphate (GTP[gamma S]) to HL-60 membranes, but their stimulatory effects on GTP[gamma S] binding were smaller than on GTP hydrolysis. The stimulatory effects of propranolol and tetracaine on GTPase and GTP[gamma S] binding were inhibited by pertussis toxin. Propranolol and tetracaine effectively activated GTP hydrolysis of a reconstituted mixture of bovine brain Gi/Go-proteins, but the concentrations of substances needed for GTPase activation were higher than in HL-60 membranes. Procaine showed stimulatory effects on the GTPase of Gi/Go-proteins. Our data show that beta AR antagonists and LAs activate pertussis toxin-sensitive G-proteins, presumably through interaction with the C-terminus of their alpha-subunits. Apparently, the lipophilic domain of beta AR antagonists and LAs is more important for G-protein activation than the basic domain. We discuss the possibility that activation of nucleoside diphosphate kinase by beta AR antagonists and LAs contributes to their stimulatory effects on GTP hydrolysis in HL-60 membranes.

Adrenergic beta-Antagonists↗
PubMed1994

N-protein kinase C isoenzymes may be involved in the regulation of various neutrophil functions.

The role of protein kinase C (PKC) isoenzymes in the regulation of cell functions is largely unknown. We studied the effects of 2-(1H-indol-3-yl)-3- [1-(3-dimethylaminopropyl)-1H-indol-3-yl]-maleinimide (Gö 6850), a selective inhibitor of c- and n-PKC isoenzymes, and 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo[2 ,3- a]pyrrolo[3, 4-c]-carbazole (Gö 6976), an inhibitor of c-PKC isoenzymes, on various human neutrophil functions. Gö 6850 inhibited 4 beta-phorbol 12-myristate 13-acetate (PMA)-, 1,2-dicaprylyl- glycerol- and chemotactic peptide-induced superoxide anion formation with half-maximal effects at 100 nM, 240 nM and 850 nM, respectively. Gö 6850 reverted PMA-mediated inhibition of chemotactic peptide-induced rises in cytosolic Ca2+ concentration with a half-maximal effect at 480 nM. Gö 6850 (1 microM) inhibited PMA-induced lysozyme release by 55%. Gö 6976 had no effect on the parameters studied. Our data suggest the following: (1) n- Rather than c-PKC isoenzymes are involved in the regulation of various human neutrophil functions. (2) Different n-PKC isoenzymes may mediate activation of NADPH oxidase by various stimuli. (3) Different n-PKC isoenzymes may be involved in the mediation of the effects of PMA on various cell functions.

Carbazoles↗
PubMed1994

Some taste substances are direct activators of G-proteins.

Amphiphilic substances may stimulate cellular events through direct activation of G-proteins. The present experiments indicate that several amphiphilic sweeteners and the bitter tastant, quinine, activate transducin and Gi/Go-proteins. Concentrations of taste substances required to activate G-proteins in vitro correlated with those used to elicit taste. These data support the hypothesis that amphiphilic taste substances may elicit taste through direct activation of G-proteins.

Animals↗