Biomedical subjects

M Horie

Publications and source records attributed to M Horie.

At least 127 records · Page 7Linked to original sources

PubMed1993

An inhibitor of squalene epoxidase, NB-598, suppresses the secretion of cholesterol and triacylglycerol and simultaneously reduces apolipoprotein B in HepG2 cells.

NB-598, a specific inhibitor of squalene epoxidase, suppressed the secretion of cholesterol and triacylglycerol from HepG2 cells into the medium. L-654,969, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, inhibited the secretion of cholesterol as potently as NB-598, but did not suppress the secretion of triacylglycerol. Both compounds decreased the intracellular cholesterol content almost equally, and neither of the compounds reduced the intracellular triacylglycerol content. The suppression of lipid secretion by NB-598 was associated with a significant reduction in apolipoprotein (apo) B secretion into the medium. Therefore, the suppression of lipid secretion by NB-598 may be caused by a reduction in the number of triacylglycerol-rich lipoprotein particles. In contrast, the suppression of cholesterol secretion by L-654,969 may be due to a modulation of lipoprotein lipid composition, since this agent did not reduce the secretion of apo B or triacylglycerol. The secretion of apo A-I was unaffected by either NB-598 or L-654,969. Pulse chase studies using [35S]methionine showed that the suppression of apo B secretion by NB-598 depended on an enhancement of intracellular degradation of apo B. These results indicate that the secretion of apo B from HepG2 cells is not regulated by the lipid synthesis alone, and suggest that the mechanism of the hypolipidemic effect of NB-598 involves the suppression of triacylglycerol-rich lipoprotein secretion from the liver as well as an inhibition of cholesterol synthesis in the liver.

Anticholesteremic Agents↗

PubMed1993

Involvement of immediate-early gene expression in the synergistic effects of steel factor in combination with granulocyte-macrophage colony-stimulating factor or interleukin-3 on proliferation of a human factor-dependent cell line.

Steel factor (SLF) synergizes with granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3) to stimulate proliferation of human factor-dependent cell line, MO7e. To elucidate molecular mechanisms underlying this synergism, induction of immediate-early genes was studied. Treatment of MO7e cells with SLF, GM-CSF, and IL-3 induced/enhanced expression of c-fos, junB, egr-1, and c-myc genes. SLF treatment of MO7e cells led to higher expression of c-fos, junB, and egr-1 genes than did treatment with GM-CSF or IL-3. However, GM-CSF and IL-3 had more prolonged effects on enhancement of the c-myc gene than SLF. Using optimal dosages for cell proliferation, induction of c-fos and junB was greater than additive with SLF plus GM-CSF or IL-3, as compared with each factor alone. Using suboptimal amounts of SLF with optimal GM-CSF or IL-3, induction of c-fos, junB, egr-1, and c-myc genes was greater than additive. De novo protein synthesis was not required for greater induction of these immediate-early genes by the combination of SLF plus GM-CSF. Based on nuclear run-on and actinomycin D experiments, the data suggest that the synergistic effects of SLF plus GM-CSF on the induction of immediate-early genes may be mediated in part at the level of transcription and mRNA stabilization for c-fos, at the level of mRNA stabilization for junB, and at the level of transcription for egr-1.

Cell Division↗

PubMed1993

Functionally distinct phospho-forms underlie incremental activation of protein kinase-regulated Cl- conductance in mammalian heart.

The regulation of cardiac Cl- conductance by cAMP-dependent protein kinase (PKA) and cellular phosphatases was studied in isolated guinea pig ventricular myocytes by using wide-tipped, perfused pipettes to record whole-cell currents. Exposure to forskolin (Fsk) or isoproterenol (Iso) elicits a Cl- conductance that results exclusively from PKA-dependent phosphorylation because it can be completely abolished, or its activation fully prevented, by switching to pipette solution containing PKI, a synthetic peptide inhibitor of PKA. The Cl- conductance activated by micromolar concentrations of either agonist reached its steady-state amplitude in 1-2 min and was deactivated promptly and entirely, usually within 2 min, upon washing out the agonist, implying a continuous high level of activity of endogenous protein phosphatases. Accordingly, intracellular application of okadaic acid or microcystin, both potent inhibitors of protein phosphatases 1 and 2A, during exposure to Fsk enhanced the steady-state Cl- conductance and slowed its deactivation after washing out the Fsk. Maximal potentiation of the conductance, by approximately 60%, was obtained with pipette concentrations of approximately 10 microM okadaic acid (or approximately 5 microM microcystin) and did not result from an increase in the apparent affinity for Fsk. In the presence of maximally effective concentrations of okadaic acid and/or microcystin, deactivation of the enhanced Cl- conductance upon washout of agonist was incomplete, with about half of the conductance persisting indefinitely. That residual conductance did not reflect continued action of PKA because it was insensitive to PKI, but was identified as a fraction of the activated Cl- conductance by its biophysical characteristics. The results suggest that complete deactivation of the PKA-regulated cardiac Cl- conductance requires dephosphorylation by a type 1 and/or 2A phosphatase, but that partial deactivation can be accomplished by activity of some other phosphatase(s). These findings are consistent with sequential phosphorylation of a protein, probably the Cl- channel itself, at two different kinds of sites. The resulting phosphoproteins can be distinguished on the basis of their different contributions to whole-cell Cl- conductance.

Animals↗

PubMed1993

Disopyramide blocks pancreatic ATP-sensitive K+ channels and enhances insulin release.

An antiarrhythmic agent, disopyramide, was found to enhance the insulin secretory capacity of Wistar rat pancreatic islets with a half-maximal concentration of 23.3 microM. Employing a patch-clamp technique, disopyramide was found to inhibit ATP-sensitive K+ (KATP) channel activity in rat pancreatic beta-cells in primary culture without altering the unitary conductance. Half-maximal inhibition was achieved by the addition of 3.6 microM disopyramide to the intracellular bathing solution in the inside-out mode, 11.0 microM to the extracellular bathing solution in the outside-out mode, and 87.4 microM in the cell-attached mode. The binding of [3H]glibenclamide to pancreatic islets was inhibited by unlabeled glibenclamide but not by unlabeled disopyramide. Based on these observations, it is concluded that disopyramide blocks pancreatic KATP channels via binding to a site(s) distinct from the sulfonylurea receptor. This effect may be causatively involved in disopyramide-induced hypoglycemia.

Adenosine Triphosphate↗

PubMed1993

Activation of Ca-permeable cation channels by myocarditis-associated antibody in guinea pig ventricular myocytes.

The pathogenesis of myocarditis and dilated cardiomyopathy is though to involve autoimmunological processes and myocardial calcium overload. Serum containing antiheart antibodies associated with a murine model of myocarditis increased [Ca2+]i in guinea pig ventricular myocytes only in the presence of extracellular Ca2+. The antiheart antibody-positive serum activated Ca(2+)-permeable cation channels that were insensitive to dihydropyridines and membrane stretch. The permeability sequence was Ba2+ > Ca2+ > Na+ approximately K+, and the single-channel conductance to Ba2+ was 12 pS. The channel was activated by extracellular application of the serum during on-cell recording, which suggests that a soluble intracellular messenger may be involved. The antibody-positive serum did not alter voltage-gated Ca2+ currents. We propose that excess Ca entry in myocarditis and dilated cardiomyopathy results from activation of a Ca(2+)-permeable cationic channel by the autoantibodies.

Animals↗

PubMed1993

Enzymatic properties of squalene epoxidase from Saccharomyces cerevisiae.

Squalene epoxidase is a microsomal membrane-associated enzyme that acts as an important regulator in the sterol biosynthetic pathway. In this study, the enzymatic properties of squalene epoxidase from Saccharomyces cerevisiae were examined. Unlike Candida squalene epoxidase, S. cerevisiae squalene epoxidase required NADPH for enzyme reaction. However, S. cerevisiae enzyme reaction did not require FAD or autologous S105 fraction. Unlike rat squalene epoxidase, the activity of S. cerevisiae was reduced by Triton X-100, a nonionic detergent. Terbinafine, an inhibitor of fungal squalene epoxidase, inhibited the enzyme in a non-competitive manner, while NB-598, an inhibitor of mammalian squalene epoxidase, barely inhibited it in a partially non-competitive manner. Thus, the properties of squalene epoxidase from S. cerevisiae were different from those of squalene epoxidase from rats and Candida, which were previously known. We propose that a species difference of squalene epoxidase exists not only between animals and fungi but between Candida and Saccharomyces.

Animals↗

PubMed1993

Serum hemolytic activity of Babesia gibsoni-infected dogs: the difference in the activity between self and nonself red blood cells.

The serum hemolytic activity of Babesia gibsoni-infected dogs varied when assayed with nonself red blood cells from different dogs, whereas it did not vary when assayed with red blood cells, irrespective of self or nonself, from a particular dog throughout the experiment. The variety in activity determined with nonself red blood cells was not related to the type of red blood cell by DEA, D and J systems. Serum hemolytic activity with self red blood cells was different in the course of infection from that with nonself red blood cells, especially in the late stage of infection, when the activity with self red blood cells decreased more rapidly than that with nonself red blood cells. The results indicate that the serum hemolytic activity of B. gibsoni-infected dogs determined with self red blood cells probably reflects the in vivo activity, suggesting that the rapid decrease in activity in the late stage of infection is a way of acquired resistances for the host to recover from hemolytic anemia in the infection. The facts that the hemolytic activity increased by heating the serum at 56 degrees C, that the osmotic fragility of red blood cells remained almost on the same during the course of infection and that Coombs' test for red blood cells of the infected animal was negative suggest that the immune-mediated hemolytic anemia is not a possible mechanism for the progressive and severe anemia in B. gibsoni-infection. The present results support the previous notion that the increased serum hemolytic activity is at least one of the causes of anemia in canine B. gibsoni-infection.

Animals↗

PubMed1993

Glucose sensitivity of ATP-sensitive K+ channels is impaired in beta-cells of the GK rat. A new genetic model of NIDDM.

In the Goto-Kakizaki rat, a new genetic model of NIDDM, insulin response to glucose is selectively impaired. To elucidate the mechanism of this abnormality, we studied the properties of ATP-sensitive K+ channels, the inhibition of which is a key step of insulin secretion induced by fuel substrates, using the patch-clamp technique. The glucose-sensitivity of KATP channels was considerably reduced in GK rats. However, the inhibitory effects of ATP on channel activity and unitary conductance were not significantly different between control and GK rats. Thus, it appears that the impaired insulinotropic action of glucose in beta-cells of GK rats is attributable to insufficient closure of the KATP channels, probably because of deficient ATP production by impaired glucose metabolism. KATP-channel activities in both control and diabetic beta-cells were found to be equally suppressed by glyceraldehyde and 2-ketoisocaproate. These results strongly suggest that the step responsible for the metabolic dysfunction of diabetic beta-cells is located within the glycolytic pathway before glyceraldehyde-3-phosphate or in the glycerol phosphate shuttle.

Adenosine Triphosphate↗

PubMed1993

Differential responses of myeloid progenitor cells from patients with myeloid leukemia and myelodysplasia to the costimulating effects of steel factor in vitro.

Steel factor (SLF, c-kit ligand), a potent costimulating cytokine in vitro for myeloid progenitor cells from normal donors, is currently being evaluated in clinical trials for effects on hematopoiesis. Based on a preliminary observation that colony-stimulating factor (CSF)-responsive myeloid progenitor cells (CFU-GM) from a few patients with acute myeloid leukemia (AML) did not respond to the costimulating effects of SLF, we evaluated responsiveness of bone marrow or blood CFU-GM from 26 patients with either AML, chronic myeloid leukemia (CML) or myelodysplastic syndrome (MDS) to the effects in vitro of SLF and/or granulocyte-macrophage CSF (GM-CSF). Cells from all 26 patients responded to the stimulating effects of GM-CSF, but marked heterogeneity was detected in each disease category to the costimulating effects of SLF. Nine of 13 patients with AML, 2 of 6 patients with CML and 4 of 7 patients with MDS had clonogenic cells that did not respond significantly to the costimulating effects of SLF. In a more limited study of cells from patients with MDS, it was noted that if the CFU-GM of that patient did not respond to SLF enhancement of CSF-induced colony formation, neither did the erythropoietin (Epo)-dependent erythroid (BFU-E) or multipotential (CFU-GEMM) cells of that patient (3 cases of refractory anemia [RA] evaluating bone marrow and in 1 case blood progenitors as well). If CFU-GM responded, BFU-E and CFU-GEMM responded (bone marrow from 1 patient with chronic myelomonocytic leukemia [CMMol]). Clinical criteria did not readily distinguish between patients who had SLF-responsive vs. -nonresponsive clonogenic cells. While the mechanistic reason for this heterogeneity in responsiveness is not clear, these differences should be carefully considered for possible clinical trials with SLF in patients with acute and chronic myeloid leukemia and MDS.

Adult↗

PubMed1993

Characterization of interleukin-7-induced changes in tyrosine phosphorylation and c-myc gene expression in normal human T cells.

Interleukin-7 (IL-7) is a growth factor involved in regulating lymphopoiesis. We have chosen to study the signal transduction pathway of IL-7 in normal human peripheral blood T lymphocytes. Two early events that occur as a consequence of specific ligand-receptor interaction were examined: activation of protein tyrosine kinases and induction of primary response gene expression. Following treatment of human peripheral blood T cells with IL-7, four cellular proteins with relative molecular weights of 95- (doublet), 105-, and 130-kd were rapidly tyrosine phosphorylated as detected by immunoblotting with an antiphosphotyrosine monoclonal antibody (MAB). The 105-kd tyrosine-phosphorylated protein was membrane-associated after IL-7 stimulation. Treatment of human peripheral blood T cells with IL-7 enhanced expression of the primary response gene c-myc approximately three-fold, as detected by Northern blotting, in the presence or absence of protein synthesis. The rate of c-myc gene transcription increased in the presence of IL-7 and could account for the observed elevation of c-myc RNA levels. In addition, IL-7 treatment induced a slight increase in c-myc message stability. Experiments performed with the protein tyrosine kinase inhibitor genistein and the serine-threonine kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7) demonstrated that these kinases were required for IL-7 enhancement of c-myc expression. Treatment with tetradecanoyl phorbol acetate (TPA), a potent activator of protein kinase C (PKC), in combination with IL-7 induced a level of c-myc expression greater than that elicited by either factor alone, suggesting that TPA and IL-7 utilize cooperative signaling pathways to increase c-myc gene expression.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1993

[Measurement and its fluctuation of urinary glucaric acid in newborns].

It is known that urinary excretion of glucaric acid(GA) is an indirect index of hepatic P-450 microenzyme induction. We measured and analyzed urinary excretion of GA in 56 newborns and 26 mothers by a new method for the inhibition of beta-glucuronidase activity and obtained the following results. 1. The concentration of urinary GA was correlated with that of urinary creatinine and total bilirubin in newborns. 2. There were no significant correlations between gestational age, sex, body weight at birth, placental weight and the urinary GA concentration. 3. The urinary excretion of GA in newborns was decreased the in first few days after birth, but a transitional increase was observed on the fifth day after birth. 4. The concentration of urinary GA was correlated with that of direct bilirubin in serum on the fifth day after birth. 5. There was a negative correlation between the urinary GA concentration on the first day after birth and that of direct bilirubin in serum on the fifth day after birth. These results suggested that hepatic P-450 microsomal enzyme was induced by bilirubin in newborns and it was possible to estimate the clinical course of jaundice by measuring the urinary excretion of GA.

Bilirubin↗

PubMed1993

Ionic mechanism of minoxidil sulfate-induced shortening of action potential durations in guinea pig ventricular myocytes.

Patch-clamp techniques were used to study pharmacological effects of minoxidil sulfate (MNXS) on the membrane currents of enzymatically isolated guinea pig ventricular myocytes. In the whole-cell current-clamp mode, MNXS (100 microM) shortened the action potential duration without affecting the resting membrane potential. This action was antagonized in part by 1 microM glibenclamide, a specific blocker of ATP-sensitive K+ channel. Under the whole-cell voltage-clamp condition, MNXS increased the time-independent outward current, in a dose-dependent manner, at voltages more positive to -73.5 mV. This MNXS-induced outward current was inhibited completely by 1 microM glibenclamide. In inside-out patch membranes, MNXS (100 microM) applied to the cytosolic side produced a reversible activation of ATP-sensitive K+ channels. This MNXS-dependent increase in the single-channel activity was abolished by increasing the ATP concentration to 3 mM or by adding 1 microM glibenclamide. Even after complete rundown of the channel activity in inside-out patches, MNXS could reactivate in part the channel in 22 of 35 patches. In addition, MNXS was found to suppress whole-cell L-type Ca++ channel currents in a dose-dependent manner. This MNXS effect on Ca++ currents was not antagonized by 1-3 microM glibenclamide. We conclude that MNXS shortens the cardiac action potential duration by both increasing ATP-sensitive K+ channel currents and decreasing L-type Ca++ channel currents.

Action Potentials↗

PubMed1992

High-performance liquid chromatography of histamine and 1-methylhistamine with on-column fluorescence derivatization.

An on-column fluorometric derivatization method was developed for the determination of histamine and 1-methylhistamine (HMs) by high-performance liquid chromatography. The system for the derivatization consisted only of a commercially available single-plunger pump and a reversed-phase C18 column supported on synthetic polymer with a mobile phase of acetonitrile and alkaline borate buffer solution containing o-phthalaldehyde as a derivatization reagent. It required no additional reaction system as for a post-column derivatization method. Injected HMs might be derivatized to a fluorophore on the inlet site of the high-performance liquid chromatographic column, followed by chromatography on the same column. Optimization of the on-column reaction conditions resulted in a simple and sensitive analytical method for the determination of HMs with excellent reproducibility and linearity of 0.05-5 micrograms/ml of both HMs. Application of this method to the determination of HMs in food samples resulted in a limit of quantification of 0.05 mg/100 g and in a greater than 95% overall mean recovery at a fortification of 0.1 mg/g of both HMs. This method was furthermore applicable to the determination of histamine released from rat peritoneal mast cells.

Animals↗

PubMed1992

Role of GTP-binding proteins in the regulation of mammalian cardiac chloride conductance.

Beta-Adrenoceptor agonists activate a time- and voltage-independent Cl- conductance in mammalian cardiac myocytes. To characterize the cellular signaling pathways underlying its regulation, wide-tipped pipettes fitted with a pipette perfusion device were used to record whole-cell current and to introduce nucleotides to the interior of guinea pig ventricular myocytes. Replacement of pipette GTP with GDP beta S prevented activation of the Cl- conductance by Iso, suggesting a requirement for G protein turnover. With GTP in the pipette, the effect of Iso could be abolished by the beta-adrenoceptor antagonist propranolol, and mimicked by histamine or forskolin. These actions of Iso and forskolin are mediated exclusively via cAMP-dependent protein kinase (PKA), because (a) maximal activation of the Cl- conductance by forskolin or pipette cAMP occluded the effect of Iso, and (b) switching to pipette solution containing a synthetic peptide inhibitor (PKI) of PKA completely abolished the Cl- conductance activated by Iso and prevented the action of forskolin, but had no further effect. These results argue against basal activation of the Cl- conductance, and make it extremely unlikely that the stimulatory G protein, Gs, has any direct, phosphorylation-independent influence. The muscarinic receptor agonists acetylcholine (ACh) and carbachol diminished, in a reversible manner, Cl- conductance activated by Iso or forskolin, but not that elicited by cAMP. The muscarinic inhibition was abolished by replacing pipette GTP with GDP beta S, or by preincubating cells with pertussis toxin (PTX), and was therefore mediated by an inhibitory G protein, presumably Gi, influencing adenylyl cyclase activity. Nonhydrolyzable GTP analogues (GTP gamma S or GppNHp) applied via the pipette did not themselves activate Cl- conductance, but rendered Cl- current activation by brief exposures to Iso or histamine, but not to forskolin, irreversible. The Cl- conductance persistently activated by Iso was insensitive to propranolol or ACh, but could still be abolished by pipette application of PKI. The data indicate that stimulation of beta-adrenergic or histaminergic receptors in the presence of nonhydrolyzable GTP analogues causes persistent activation of Gs and uncouples it from the receptors. We conclude that autonomic regulation of cardiac Cl- conductance reflects accurately the underlying modulation of adenylyl cyclase activity and, hence, that this system is a suitable mammalian model for in situ studies of the interactions between adenylyl cyclase, Gs, Gi, and forskolin.

Acetylcholine↗

PubMed1992

Comparative studies of ATP sensitive potassium channels in heart and pancreatic beta cells using Vaughan-Williams class Ia antiarrhythmics.

OBJECTIVE: Actions of cibenzoline and disopyramide, agents with Vaughan-Williams class Ia antiarrhythmic action, on ATP sensitive K+ (KATP) channels were examined in heart and pancreatic beta cells. METHODS: Single ventricular myocytes and beta cells were prepared enzymatically from adult Wistar rat hearts and pancreatic islets. Using patch clamp techniques, KATP channel activities were recorded in whole cell and single channel modes. In whole cell experiments, myocytes were bathed with Tyrode's medium (34 degrees C); inside out patches were bathed with internal solutions (22-24 degrees C) containing 1 microM ATP and varying concentrations of cibenzoline or disopyramide. Myocytes were voltage clamped at -40 mV and glibenclamide blockade conductance was produced by cromakalim. RESULTS: Micromolar concentrations of both cibenzoline and disopyramide suppressed cromakalim induced conductance. When applied to the cytosolic surface of the cell membrane in inside out configuration, both drugs reversibly inhibited single KATP channel activities. Neither unitary conductance nor intraburst fast kinetics was affected by the compounds. At a holding potential of -40 mV under symmetrical approximately 150 mM K+ conditions, half maximum doses (IC50) were 0.9 microM [Hill coefficient (h) = 1.3] for cibenzoline induced block of cardiac KATP channels and 1.8 microM (h = 1.0) for disopyramide block. At +40 mV, IC50 for cibenzoline block was 1.4 microM (h = 0.9). Thus there was little voltage dependence in cibenzoline induced channel block. A similar IC50 value of 2.5 microM (h = 1.2 at -60 mV under symmetrical approximately 150 mM K+) was observed for cibenzoline induced block of KATP channels. CONCLUSIONS: Near therapeutic concentrations of cibenzoline and disopyramide inhibit KATP channel activities in both heart and pancreatic beta cells. This may be causally related to the fasting hypoglycaemia which is sometimes reported in patients receiving the drugs. These antiarrhythmic agents may also modulate myocardial electrical properties during hypoxia or ischaemia.

Adenosine Triphosphate↗

PubMed1992

Pipette GTP is essential for receptor-mediated regulation of Cl- current in dialysed myocytes from guinea-pig ventricle.

1. Wide-tipped, low-resistance (approximately 1 M omega) pipettes were used to record the whole-cell Cl- current activated by cAMP-dependent protein kinase (PKA) in guinea-pig ventricular myocytes internally dialysed with or without GTP. Without GTP in the pipette, the response to 1 microM-isoprenaline declined with time and eventually disappeared, usually within approximately 20 min of rupturing the membrane and beginning cell dialysis. 2. This rundown of the isoprenaline response occurred more quickly with wider, lower-resistance pipette tips. 3. After complete rundown of the isoprenaline response, histamine (10 microM), another agonist known to elicit the Cl- current, also had no effect, but extracellular forskolin (1 microM) or intrapipette cAMP (1 mM) could still readily elicit the Cl- current. 4. In contrast, with 100 microM-GTP in the pipette, the response to 1 microM-isoprenaline was well maintained for periods greater than 20 min. But, if GTP was then withdrawn from the pipette, a rundown of the isoprenaline response was seen comparable to that in the experiments begun with GTP-free pipette solution. Moreover, in experiments begun without pipette GTP, the addition of 100 microM-GTP to the pipette solution, after the response to isoprenaline had disappeared, was able to restore that Cl- current response. 5. With GTP in the pipette, the forskolin-induced Cl- current could be suppressed by concurrent exposure to carbachol (10 microM). That inhibition was not seen in myocytes pretreated with pertussis toxin. In untreated myocytes dialysed with GTP-free pipette solution, after disappearance of the isoprenaline response, the muscarinic receptor-mediated inhibition was itself abolished. 6. We confirm that both beta-adrenoceptor-mediated activation of the Cl- current by isoprenaline, and muscarinic receptor-mediated inhibition of the forskolin-induced Cl- current, are mediated by G proteins, and conclude that the disappearance of both receptor-mediated responses during whole-cell recording with GTP-free pipette solution reflects the fall of cellular [GTP] below the level required to maintain G protein-dependent signal transduction.

Animals↗

PubMed1992

Effect of an inhibitor of squalene epoxidase, NB-598, on lipid metabolism in Hep G2 cells.

NB-598, a potent inhibitor of squalene epoxidase, inhibited cholesterol synthesis from [14C]acetate and induced intracellular squalene accumulation in Hep G2 cells. NB-598 inhibited cholesterol synthesis from [14C]acetate, [3H]mevalonate, and [3H]squalene, but not from [3H]2,3-oxidosqualene in Hep G2 cells. It reduced cholesterol ester synthesis remarkably in the absence of exogenous cholesterol. This compound did not have any effect on the synthesis of ubiquinone and dolichol. When Hep G2 cells were prelabeled with micellar [3H]cholesterol, NB-598 did not affect the excretion of bile acid incorporated from [3H]cholesterol. However, NB-598 decreased the secretion of free and esterified cholesterol, triacylglycerol, and phospholipids, and increased the secretion of squalene. NB-598 is thought not only to inhibit cholesterol synthesis, but also to inhibit the secretion of lipids.

Anticholesteremic Agents↗

PubMed1992

Impaired glucose sensitivity of ATP-sensitive K+ channels in pancreatic beta-cells in streptozotocin-induced NIDDM rats.

ATP-sensitive K+ channels (KATP channels) are known to play a key role in the cellular mechanism of insulin secretion from pancreatic beta cells. In order to examine the possible impairment of KATP channel function in non-insulin-dependent diabetes mellitus (NIDDM), we have studied the properties of the KATP channels in single beta cells of neonatally streptozotocin-induced diabetic rats (NSZ rats) using the patch-clamp technique. The unitary conductance of the channel in diabetic beta-cells was virtually identical to that in control beta cells and there was no difference in the sensitivity to ATP and glibenclamide of KATP channels between the NIDDM and control groups. In response to glucose, the activity of the KATP channels was diminished in a dose-dependent manner in both control and diabetic cells. However, the inhibition of the KATP channels in beta-cells of NSZ rats was significantly less than that in control cells. Even in the presence of 11.1 mM glucose, the openings of a few single KATP channels were consistently observed in cell-attached patch membranes of diabetic, but not control, beta-cells. Thus, it appears that the impaired insulinotropic action of glucose in beta-cells in NSZ rats is associated with a reduced sensitivity of the KATP channel to glucose, but not to ATP, presumably due to a deficiency in glucose metabolism.

Adenosine Triphosphate↗