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Biomedical subjects

I Niki

Publications and source records attributed to I Niki.

At least 37 records · Page 2Linked to original sources
PubMed1996

Ca2+ signaling and intracellular Ca2+ binding proteins.

Changes in cytosolic Ca2+ concentrations evoke a wide range of cellular responses and intracellular Ca(2+)-binding proteins are the key molecules to transduce Ca2+ signaling via enzymatic reactions or modulation of protein/protein interations (Fig.1). The EF hand proteins, like calmodulin and S100 proteins, are considered to exert Ca(2+)-dependent actions in the nucleus or the cytoplasm. The Ca2+/phospholipid binding proteins are classified into two groups, the annexins and the C2 region proteins. These proteins, distributed mainly in the cytoplasm, translocate to the plasma membrane in response to an increase in cytosolic Ca2+ and function in the vicinity of the membrane. Ca2+ storage proteins in the endoplasmic or sarcoplasmic reticulum provide the high Ca2+ capacity of the Ca2+ store sites, which regulate intracellular Ca2+ distribution. The variety and complexity of Ca2+ signaling result from the cooperative actions of specific Ca(2+)-binding proteins. This review describes biochemical properties of intracellular Ca(2+)-binding proteins and their proposed roles in mediating Ca2+ signaling.

Animals↗
PubMed1996

Increase in insulin release from rat pancreatic islets by quinolone antibiotics.

1. The present study was undertaken to elucidate the mechanism(s) of hypoglycaemia caused by quinolone antibiotics. We investigated the effects of various quinolone antibiotics on insulin release in rat pancreatic islets. 2. At a non-stimulatory concentration of 3 mM glucose, lomefloxacin (LFLX) or sparfloxacin at 1 mM and pipemidic acid (0.1-1 mM) induced slight insulin release but tosufloxacin or enoxacin up to 100 microM did not. 3. At the stimulatory concentration of 10 mM glucose, all quinolones augmented insulin release in a dose-dependent manner. LFLX (100 microM) shifted the dose-response curve of glucose-induced insulin release to the left without altering the maximal response. 4. At 10 mM glucose, LFLX (100 microM) increased insulin release augmented by forskolin (5 microM) or 12-O-tetradecanoyl phorbol-13-acetate (100 nM) but not by raising the K+ concentration from 6 to 25 mM. 5. Verapamil (50 microM) or diazoxide (50-400 microM) antagonized the insulinotropic effect of LFLX. 6. These data suggest that quinolone antibiotics may cause hypoglycaemia by increasing insulin release via blockade of ATP-sensitive K+ channels.

4-Quinolones↗
PubMed1996

Ca2+/calmodulin and cyclic 3,5' adenosine monophosphate control movement of secretory granules through protein phosphorylation/dephosphorylation in the pancreatic beta-cell.

We observed the movement of insulin granules in living transformed hamster pancreatic beta-cells (HIT T15) with a light microscope, where secretory granules are moving in the cytoplasmic space. Velocity of the typical granule movement was approximately 1.5 microns/sec. A stimulatory concentration of glucose activated the movement of the secretory granules. Forskolin, an activator of adenylate cyclase, increased the movement, resulting in changes in intracellular localization of the granules. Acetylcholine also activated the granule movement, whereas high K+ and tolbutamide, which cause Ca2+ influx through the voltage-dependent Ca2+ channel, had only little effect. The movement was abolished by BAPTA, the intracellular Ca2+-chelator. Activation of protein kinase C by 12-O-tetradecanoyl-phorbol 13-acetate failed to affect this movement. The motile events were inhibited by the calmodulin antagonist, W-7, and dramatically increased by okadaic acid, an inhibitor of protein phosphatases 1 and 2A. These results suggest protein phosphorylation by Ca2+/calmodulin- and cAMP-dependent protein kinases play a positive role in the control of the insulin granule movements, which results in potentiation of insulin release from the pancreatic beta-cell.

Acetylcholine↗
PubMed1995

The associations between alcohol drinking and dietary habits and blood pressure in Japanese men.

OBJECTIVE: To clarify the relationships between blood pressure and alcohol, nutrients and electrolytes intakes in Japanese men. DESIGN AND METHOD: A dietary survey was conducted in a rural population of Japan by the 2-day dietary record method, and blood pressure was measured with a standard sphygmomanometer. Blood pressure levels, nutrients and electrolytes intakes were compared among the non-drinkers and the tertiles of the alcohol-drinking subjects. The relationships between blood pressure and nutrients, electrolytes and alcohol intakes were also determined by multiple regression analysis. RESULTS: Age and systolic blood pressure (SBP) were positively, and percentage of energy from fat and carbohydrates was negatively, related to the drinking categories. Univariate analysis showed that SBP was significantly related to age, body mass index (BMI) and alcohol intake, and diastolic blood pressure (DBP) was also significantly related to age, BMI and alcohol intake. Both SBP and DBP had a significant inverse relationship with the percentage of energy from fat (P < 0.01). Both SBP and DBP were significantly related to drinking categories when the effects of age, BMI and percentage energy from fat intake on blood pressure were adjusted for (P < 0.001). Multiple regression analysis revealed SBP to be significantly and positively associated with age, BMI and alcohol intake, and negatively associated with potassium intake, whereas DBP was significantly and positively associated with BMI and total energy intake, and was negatively associated with potassium and the percentage of energy intake from fat and carbohydrates. CONCLUSION: The positive association between alcohol drinking and blood pressure persisted even after consideration of the effects of age, BMI and other macronutrient and electrolytes intakes. The reduction of alcohol intake should be an important public health strategy in the primary prevention of hypertension in this population.

Adult↗
PubMed1994

A role of calcyclin, a Ca(2+)-binding protein, on the Ca(2+)-dependent insulin release from the pancreatic beta cell.

Exocytosis is an important example of cell activation. Ca2+ and calcium-binding proteins are considered to modulate signal transduction in exocytosis. We examined the role of calcyclin, calcium-binding protein, in the stimulus-secretion coupling in pancreatic beta cells. The presence of calcyclin in these cells was demonstrated immunologically. We permeabilized rat pancreatic islets with streptolysin-O and examined the effects of calcyclin on insulin release. The Ca(2+)-stimulated insulin release was enhanced by calcyclin, in a dose-dependent manner, whereas this calcium-binding protein had no effect on insulin release from islets in low Ca2+ buffer or from the islets not subjected to the streptolysin-O treatment. Calgizzarin, another member of the S-100 protein family, had no apparent effect on the Ca(2+)-stimulated secretion under parallel conditions. An anticalcyclin antibody suppressed the increase in insulin release induced by calcyclin. We propose that calcyclin may be involved in signal transduction of the Ca(2+)-induced release of insulin.

Animals↗
PubMed1993

Presence and possible involvement of Ca/calmodulin-dependent protein kinases in insulin release from the rat pancreatic beta cell.

Roles of Ca/calmodulin-dependent protein kinase II (Ca/CaM kinase II) and myosin light chain kinase (MLCK) in insulin release from rat pancreatic islets were investigated. Western blotting using polyclonal antibody to Ca/CaM kinase II suggested the presence of this kinase in the pancreatic islets. Extracts of pancreatic islets phosphorylated exogenous myosin light chain, which was inhibited by ML-9, an inhibitor of MLCK. KN-62 and KN-93, inhibitors of Ca/CaM kinase II, and ML-9 at microM concentrations inhibited insulin release stimulated by glucose or high K+. KN-62 and KN-93, but not ML-9, inhibited insulin release increased by glucose and forskolin, an activator of adenylate cyclase. These inhibitors had no effect on insulin release evoked by 12-O-tetradecanoyl phorbol-13-acetate, an activator of Ca(2+)-sensitive, diacylglycerol-dependent protein kinase. These results suggest that Ca/CaM kinase II and MLCK may participate in the control of insulin release.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

Characterization and solubilization of the sulphonylurea receptor in rat brain.

The binding characteristics of the sulphonylurea receptor were investigated using rat brain microsomes. Scatchard plots for binding of [3H]glibenclamide, a potent sulphonylurea which inhibits the ATP-sensitive K-channel, suggested the presence of both high and low affinity binding sites with Kd of 0.58 and 17 nM, and beta max of 123 and 392 fmol/mg protein, respectively. When brain microsomes were solubilized with CHAPS, high affinity sites were retained with Kd and beta max of 1.2 nM and 42.1 fmol/mg protein, respectively, whereas the low affinity sites disappeared. The specific binding was displaced by non-labelled glibenclamide, meglitinide, and tolbutamide with IC50 at 5 nM, 25 microM and 130 microM, respectively. ATP and GTP inhibited [3H]glibenclamide binding in a Mg-dependent manner whereas the inhibition by ADP and GDP was Mg-independent [3H]Glibenclamide binding to the solubilized receptor was similarly inhibited by those nucleotides. Diazoxide inhibited [3H]glibenclamide binding in the presence of MgATP, but after CHAPS-solubilization diazoxide failed to inhibit [3H]glibenclamide binding even with MgATP. These findings suggest the brain sulphonylurea receptor has similar features to the beta-cell receptor. However, inhibition of the binding by nucleotides is not identical, possibly reflecting differences in the nucleotide-binding subunit.

ATP-Binding Cassette Transporters↗
PubMed1992

Stimulation of insulin release by vasopressin in the clonal beta-cell line, HIT-T15: the role of protein kinase C.

We have studied the effects of vasopressin and tetradecanoyl phorbol acetate (TPA) on cytosolic free Ca2+ ([Ca2+]i) and insulin release in HIT-T15 beta-cells. Saturable binding of [3H] [Arg8]-vasopressin to HIT cell microsomes indicated a single class of receptors with a dissociation constant (Kd) of 2.5 nM and a total number of binding sites (Bmax) equal to 120 fmol/mg protein. [Arg8]-vasopressin (0.1-100 nM) elicited dose-dependent insulin release from HIT cells by up to 25-fold. This increase was dependent on the presence of extracellular glucose and was blocked by omission of extracellular Ca2+ or addition of verapamil. The stimulation was biphasic; a rapid but short-lived large increase in release was followed by a smaller sustained rise. Vasopressin also evoked a marked, concentration-dependent increase in [Ca2+]i which was also biphasic; an initial spike was followed by a sustained elevation. This increase also required glucose and was blocked by the absence of extracellular Ca2+ or the addition of verapamil. Pretreatment of the cells with TPA overnight to deplete protein kinase C activity did not affect the [Ca2+]i or insulin responses to vasopressin. However, short-term exposure to TPA markedly reduced glucose-induced steady-state [Ca2+]i, despite potentiating glucose-stimulated insulin release sevenfold, and blocked the [Ca2+]i increase induced by vasopressin. These inhibitory effects of TPA were absent in protein kinase C-depleted cells and were prevented by staurosporine. TPA had no significant effect on vasopressin-induced insulin release. Vasopressin did not modify the activity of ATP-sensitive K+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1991

Possible involvement of protein phosphorylation in the regulation of the sulphonylurea receptor of a pancreatic beta-cell line, HIT T15.

The possible role of protein phosphorylation in modulation of [3H]glibenclamide binding to the sulphonylurea receptor, a putative ATP-sensitive K-channel, was investigated in the cloned pancreatic beta-cell line, HIT T15. Diazoxide, an opener of ATP-sensitive K-channels, increased HIT cell 86Rb-efflux, inhibited insulin secretion and decreased non-competitively [3H]glibenclamide binding to intact HIT cells. ATP-depletion reduced the [3H]glibenclamide binding activity of intact cells but did not change diazoxide-insensitive binding. Although diazoxide alone did not change the binding of [3H]glibenclamide to HIT cell membranes, the simultaneous presence of MgATP revealed an inhibition of [3H]glibenclamide binding by diazoxide. This effect of MgATP was reproduced by MgATP gamma S, but not by MgADP, MgAMP-PNP or MgAMP-PCP. These findings suggest that protein phosphorylation may be involved in the response of ATP-sensitive K-channels to diazoxide.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Characterization of the solubilized glibenclamide receptor in a hamster pancreatic beta-cell line, HIT T15.

The glibenclamide receptor, a putative ATP-sensitive K+ channel in the hamster pancreatic beta-cell line HIT T15, was solubilized by using the zwitterionic detergent CHAPS. [3H]Glibenclamide binding was dependent on the incubation time and on the concentration of soluble membrane protein. Over 80% of [3H]glibenclamide bound could be displaced with 1 microM non-labelled glibenclamide. The curve relating specific binding to the concentration of [3H]glibenclamide (1-20 nM) showed saturation kinetics. Scatchard analysis suggested a single class of non-interacting binding sites with a Kd of 3.3 nM and a Bmax. of 90 fmol/mg of protein. [3H]Glibenclamide binding to solubilized membranes was inhibited by glibenclamide, tolbutamide and meglitinide. The relative potency of these agents on binding of [3H]glibenclamide to solubilized membranes was similar to that observed with microsomal preparations and paralleled their effects on K-ATP channel activity, measured as 86Rb efflux. These data show that the sulphonylurea receptor in the pancreatic beta-cell can be solubilized in an active form retaining specificity for sulphonylureas. ADP, which inhibits [3H]glibenclamide binding to microsomal preparations or intact HIT beta-cells, did not inhibit binding to the solubilized receptor. Incubation of intact HIT beta-cells with 125I-glibenclamide derivative followed by exposure to u.v. light resulted in covalent labelling of a peptide of 65 kDa on SDS/PAGE. The extent of labelling increased with 125I-glibenclamide derivative concentration (1-20 nM) and was inhibited in the presence of excess unlabelled glibenclamide.

Affinity Labels↗
PubMed1990

The beta-cell glibenclamide receptor is an ADP-binding protein.

The effects of ADP on [3H]glibenclamide binding to membranes and whole cells, the activity of the ATP-sensitive K+ channel (K-ATP channel), intracellular Ca2+ concentration and insulin secretion were studied in a hamster pancreatic beta-cell line, HIT T15. ADP dose-dependently inhibited [3H]glibenclamide binding to membranes and to whole cells in a competitive manner. ADP-agarose also inhibited the binding to whole cells. The activity of the K-ATP channel was assayed by measuring 86Rb efflux from whole cells. ADP inhibited the 86Rb efflux elicited either by diazoxide or by ATP depletion. In the presence, but not in the absence, of extracellular Ca2+, ADP evoked a rapid and sustained increase in intracellular Ca2+ concentration as estimated with the fluorescent dye quin 2. Insulin release from HIT cells was also increased by 0.5-2 mM-ADP in the presence of 0.5 mM-glucose. These effects of ADP on glibenclamide binding, K-ATP channel activity and insulin release were specific for ADP, and were not reproduced by any other nucleotide so far tested. The present findings strongly suggest that ADP and sulphonylureas have common binding sites on the extracellular side of beta-cell plasma membranes, where they inhibit the activity of the K-ATP channel, resulting in an increase in intracellular Ca2+ concentration and insulin release.

ATP-Binding Cassette Transporters↗
PubMed1989

The dependence on intracellular ATP concentration of ATP-sensitive K-channels and of Na,K-ATPase in intact HIT-T15 beta-cells.

We have studied the effects of changes of intracellular ATP concentration ([ATP]i) on the activity of ATP-sensitive K-channels (IK(ATP] and of Na,K-ATPase in intact cells of the insulin-secreting cell-line HIT-T15. Pre-exposure of HIT beta-cells to oligomycin caused a dose-dependent reduction in [ATP]i. Marked activation of IK(ATP) activity was found when ATP was lowered below 3 mM. Na,K-ATPase was progressively inhibited as ATP was lowered to 1.5 mM. These data demonstrate that changes in intracellular ATP in the millimolar range markedly influence the activity of two beta-cell membrane proteins having affinities for ATP in the micromolar range. This suggests that submembrane [ATP] may be considerably below the measured bulk cytosolic concentration. The findings also support the proposed role of intracellular ATP in mediating effects of changes in glucose concentration on the activity of beta-cell IK(ATP) and insulin secretion.

Adenosine Triphosphate↗
PubMed1989

ATP-sensitive K-channels in HIT T15 beta-cells studied by patch-clamp methods, 86Rb efflux and glibenclamide binding.

ATP-sensitive K-channels in the cloned beta-cell line HIT T15 were studied by patch-clamp methods; by measurement of 86Rb efflux; and by [3H]glibenclamide binding to isolated membrane preparations. In inside-out patches a 50 pS K-channel was found which was blocked by ATP or tolbutamide applied to the intracellular membrane surface. A minimum estimate of about 500 channels per beta-cell was obtained by combining whole-cell and single-channel data. The rate of efflux of 86Rb from 86RbCl-loaded HIT cells was markedly increased by intracellular ATP-depletion; 86Rb-efflux was progressively inhibited by increasing concentrations of glibenclamide or tolbutamide. In non-ATP-depleted cells, diazoxide elicited a concentration-dependent stimulation of 86Rb-efflux which was completely blocked by 1 microM glibenclamide. Isolated membranes showed dose-dependent saturable binding of [3H]glibenclamide to both high (Kd = 1.12 nM) and low (Kd = 136 nM) affinity binding sites. We estimate about 5000 high-affinity binding sites per cell. [3H]-glibenclamide binding was inhibited by tolbutamide (IC50 = 125 microM) but was not affected by diazoxide. ADP (0.5 or 1.0 mM) markedly reduced binding; other nucleotides tested were ineffective.

Adenosine Diphosphate↗
PubMed1989

Insulin release by D-glucose anomers in a non-insulin-dependent diabetes rat model.

The alpha anomer of D-glucose is more potent than the beta anomer in stimulating insulin release. We have studied the effects of D-glucose anomers on insulin release from the perfused pancreas isolated from a rat model of non-insulin-dependent diabetes (NIDD) induced by streptozotocin injection at 2 days of age. Insulin release from the pancreas of the diabetic rat in response to 10 mM alpha-D-glucose was markedly impaired, while insulin response to the same concentration of beta-D-glucose was only slightly reduced as compared to that in the control pancreas. Thus, the pancreatic B cell of the diabetic rat did not discriminate between the alpha and beta anomers of D-glucose. Insulin release induced by 5 mM D-glyceraldehyde was decreased in the diabetic pancreas, while insulin release induced by 0.15 mg/ml tolbutamide did not differ from that in the control pancreas. Glucose oxidation in the islets isolated from the diabetic pancreas was not lower than that in comparable control islets. Treatment of the diabetic pancreas with 5 microM forskolin or 0.15 mg/ml tolbutamide did not restore its defective discrimination between the two anomers, although forskolin potentiated insulin release more markedly in the diabetic pancreas. The findings may provide some insight into the pathophysiology of the pancreatic B cell in NIDD.

Animals↗