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M Kao

Publications and source records attributed to M Kao.

At least 37 records · Page 2Linked to original sources
PubMed1988

Possible role of cytosolic free calcium concentrations in mediating insulin resistance of obesity and hyperinsulinemia.

Insulin- and glyburide-stimulated changes in cytosolic free calcium concentrations [( Ca2+]i) were studied in gluteal adipocytes obtained from six obese women (139 +/- 3% ideal body wt) and six healthy, normal weight age- and sex-matched controls. Biopsies were performed after an overnight fast and twice (at 3 and 6 h) during an insulin infusion (40 mU/m2 per min) (euglycemic clamp). In adipocytes obtained from normal subjects before insulin infusion, insulin (10 ng/ml) increased [Ca2+]i from 146 +/- 26 nM to 391 +/- 66 nM. Similar increases were evoked by 2 microM glyburide (329 +/- 41 nM). After 3 h of insulin infusion, basal [Ca2+]i rose to 234 +/- 21 nM, but the responses to insulin and glyburide were completely abolished. In vitro insulin-stimulated 2-deoxyglucose uptake was reduced by insulin and glucose infusion (25% stimulation before infusion, 5.4% at 3 h, and 0.85% at 6 h of infusion). In obese patients, basal adipocyte [Ca2+]i was increased (203 +/- 14 nM, P less than 0.05 vs. normals). The [Ca2+]i response demonstrated resistance to insulin (230 +/- 23 nM) and glyburide (249 +/- 19 nM) stimulation. Continuous insulin infusion increased basal [Ca2+]i (244 +/- 24 nM) and there was no response to either insulin or glyburide at 3 and 6 h of study. Rat adipocytes were preincubated with 1-10 mM glucose and 10 ng/ml insulin for 24 h. Measurements of 2-deoxyglucose uptake demonstrated insulin resistance in these cells. Under these experimental conditions, increased levels of [Ca2+]i that were no longer responsive to insulin were demonstrated. Verapamil in the preincubation medium prevented the development of insulin resistance.

Adipose Tissue↗
PubMed1988

Relationship between cytosolic free calcium concentration and 2-deoxyglucose uptake in adipocytes isolated from 2- and 12-month-old rats.

We have examined the relationship between insulin-stimulated 2-deoxyglucose uptake and cytosolic free calcium concentrations, [( Ca2+]i), in adipocytes isolated from 2- and 12-month-old rats. The basal rates of glucose uptake and the levels of cytosolic Ca2+ were only minimally reduced in 12-month-old animals. In contrast, insulin-stimulated glucose up-take and [Ca2+]i were significantly decreased in older adipocytes at all insulin concentrations (P less than 0.01). When the rate of glucose uptake was plotted as a function of [Ca2+]i, insulin-stimulated glucose uptake was almost identical in older and younger animals at any given level of [Ca2+]i. Similar to insulin, glyburide and K+ increased [Ca2+]i in both younger and older adipocytes. However, glyburide- and K+-elicited responses were lower in older rats (P less than 0.01). The effects of insulin, glyburide, and K+ on [Ca2+]i are mediated via voltage-dependent Ca2+ channels. Thus, the present observations suggest an impairment in either function and/or availability of the voltage-dependent Ca2+ channels in older animals. This was supported by the finding of reduced [3H]nitrendipine binding in adipocytes isolated from older animals (6.5% vs. 3.3% in 2- and 12-month-old rats, respectively; P less than 0.01). The results of these experiments indicate that the postreceptor changes in adipocyte responsiveness to insulin in aging may involve inadequate increases in [Ca2+]i. The latter probably occurs as a result of decreased availability and/or function of the voltage-dependent calcium channels.

Adipose Tissue↗
PubMed1987

The existence of an optimal range of cytosolic free calcium for insulin-stimulated glucose transport in rat adipocytes.

We have examined the effects of extracellular and intracellular Ca2+ concentrations upon basal and insulin-stimulated 2-deoxyglucose uptake in isolated rat adipocytes. In the absence of extracellular Ca2+, both basal and insulin-stimulated glucose uptake were significantly reduced. Insulin-stimulated glucose transport was optimal at 1 and 2 mM Ca2+. Further increases in extracellular Ca2+ concentration (3 mM) significantly diminished insulin-stimulated glucose uptake. When intracellular Ca2+ concentrations were augmented by ionomycin (1 microM), insulin-stimulated glucose uptake was significantly reduced at extracellular Ca2+ concentrations of 2 and 3 mM. The levels of intracellular free Ca2+ concentrations were then measured with Ca2+ indicator fura-2. The correlation between the levels of intracellular free Ca2+ and the magnitude of insulin-stimulated glucose uptake revealed that the optimal effect of insulin is observed at Ca2+ levels between 140 and 370 nM. At both extremes outside of this window, both low and high levels of intracellular Ca2+ result in diminished cellular responsiveness to insulin. These data suggest that intracellular calcium concentrations may exert a dual role in the regulation of cellular sensitivity to insulin. First, there must exist a minimal concentration of intracellular calcium to promote insulin action. Second, increased levels of intracellular calcium may provide a critical signal for diminution of insulin action.

Adipose Tissue↗
PubMed1987

Nuclear translocation of the insulin receptor. A possible mediator of insulin's long term effects.

The translocation of occupied surface insulin receptors to the nuclei of isolated hepatocytes was studied using the biologically active photosensitive insulin derivative, B2(2-nitro-4-azidophenylacetyl)-des-PheB1-insulin (NAPA-DP-insulin). When hepatocytes were photolabeled at 4 degrees C, extensively washed, and then further incubated at 37 degrees C for 1 h, photolabeled insulin receptors, which were initially localized to the cell surface, accumulated in the subsequently isolated nuclei. When the isolated nuclei were solubilized and subjected to polyacrylamide gel electrophoresis and radioautography, labeled proteins with Mr identical to the cell surface insulin receptor were detected. Light microscopic radioautography of nuclei isolated from cells incubated for 1 ha at 37 degrees C demonstrated that 28% of these nuclei were specifically labeled with one or more grains. Electron microscopic radioautography of intact cultured hepatocytes, incubated 60 min at 37 degrees C, revealed that 26% of the thin-sectioned nuclei contained at least a single grain and 8.3% of the total cell-associated associated grains were located over the nuclei. Only 1.6% of grains were localized to lysosomes. In contrast, if photolabeled hepatocytes were incubated at 4 degrees C for up to 2 h, negligible accumulation of nuclear radioactivity was observed by polyacrylamide gel electrophoresis on light or electron microscopic radioautography. Conclusions are as follows. Occupied cell surface insulin receptors can internalize and translocate to the nucleus of intact hepatocytes by a time- and temperature-dependent mechanism. Accumulation and possible degradation of insulin receptors in lysosomes involves only a small percentage of the receptors internalized. Nuclear translocation of occupied cell surface insulin receptors may be a mechanism which mediates insulin's long term effects.

Affinity Labels↗
PubMed1987

Insulin and glyburide increase cytosolic free-Ca2+ concentration in isolated rat adipocytes.

We investigated the effect of insulin and a hypoglycemic sulfonylurea agent glyburide on cytosolic free-Ca2+ concentrations [( Ca2+]i) in isolated rat adipocytes. Both insulin and glyburide increased [Ca2+]i in a dose-dependent manner. Half-maximal effects were seen at 0.5 ng/ml of insulin and 0.5 microM glyburide. Nifedipine (25 microM), a Ca2+-channel blocker, inhibited the effect of both agents. The effect of insulin on [Ca2+]i was 40 and 70% potentiated by ambient glucose concentrations at 180 and 300 mg/dl, respectively. Depolarizing doses of potassium (40 mM) induced an increase in cytosolic Ca2+ that was also inhibited by nifedipine. It is suggested that both insulin and glyburide increase cytosolic free Ca2+ levels at least in part by promoting Ca2+ influx through voltage-dependent Ca2+ channels.

Adipose Tissue↗
PubMed1985

[Borna virus infection (Borna disease) in naturally and experimentally infected animals: its significance for research and practice].

In this survey article on Borna Disease-many years after the review of Zwick (1939)-again a modern comprehensive summary of "Borna Disease virus infection" is given. The infection occurs in horses and sheep, furthermore, in laboratory animal species inoculated experimentally; its clinical, virological and neuropathological features have been described in numerous presentations. Clinical symptoms in naturally and experimentally infected animals are characterized by initial alterations in the sensorium. The neurological symptomatology of the disease (disturbances in coordination, motor, sensory and vegetative symptoms) reflect the presumed localisation of the virus in various brain areas and the course of the disease supports the assumption of intraneural spread of the agent. In horses the incidence is highest during spring. Experimental infections show an exceptionally broad spectrum of infectible animals extending from higher mammals to birds. Our investigations make it clear that we have to differentiate between infections followed by disease (e.g. horse, rabbit, older rat) and persistent infections without overt clinical symptoms (mouse, chicken). Persistent infections are sometimes associated with fine alterations in behaviour (tree shrew) or decreased learning ability (mice). Borna Disease virus, which has not been characterized up to now, is known to grow without any cytopathic effect in tissue cultures. All tested cell lines (including those from man) could be infected. The investigations indicate that Borna Disease virus comprises an enveloped RNS-containing agent. The infection induces the production of specific antigens such as a complex known as the soluble antigen, and a 14500 dalton protein. Under natural conditions and in experimentally infected animals antibodies are produced against such soluble proteins and determinants involved in neutralization of the virus. In the central nervous system (CNS) a local immune response accompanied by the production of oligoclonal immunoglobulins is demonstrable. Besides the humoral reaction it was possible to study the influence of cellular defence mechanisms on the disease process in monkeys, rats and rabbits. Histopathologically, Borna Disease is characterized by a non-purulent inflammation of the brain and the spinal cord. Most alterations are found in the grey matter, mainly in the Ammon's horn, olfactory lobe, caudate nucleus, thalamus, lamina quadrigemina and in he cerebellar nuclei. The perivascular infiltrations, consisting of lymphocytes, histiocytes and plasma cells are most conspicuous. Occasionally, degenerative alterations are observed in ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Adaptation of Borna disease virus to the mouse.

Borna disease virus has been adapted to the mouse, which required at least three passages in rat brains. Genetic specificity as studied with five inbred mouse strains was not evident. Newborn mice inoculated intracerebrally expressed antigen in neurons and remained persistently infected, with up to 10(7) infectious units per gram of brain tissue. Animals infected at different ages developed no disease and had high titres of antibodies.

Adaptation, Biological↗
PubMed1984

The role of the glucose transport system in the postreceptor defect in insulin action associated with human aging.

In an attempt to elucidate the cellular mechanisms of the insulin resistance associated with aging, insulin-mediated glucose transport was studied in isolated adipocytes obtained from 14 elderly subjects (mean age +/- SE, 69 +/- 2 yr) and 11 nonelderly (40 +/- 4 yr) subjects using the nonmetabolized glucose analogue 3-O-methylglucose. In elderly subjects with normal oral glucose tolerance tests, maximal insulin-stimulated glucose transport was reduced compared to nonelderly control levels [1.26 +/- 0.17 (+/- SE) vs. 1.96 +/- 0.26 pmol/2 X 10(5) cells X 15 sec; P less than 0.025). Elderly subjects with nondiagnostic oral glucose tolerance tests had more marked reductions in basal, submaximal, and maximal stimulated rates of glucose transport compared to the nonelderly group. The elderly group with the greatest decrease in in vitro glucose transport also had the greatest decrease in in vivo insulin-stimulated glucose disposal, whereas the elderly subjects with the mildest in vitro defect also had the smallest reduction in in vivo glucose disposal. A significant positive relationship existed between the maximal rate of in vitro glucose transport and the maximal rate of in vivo glucose disposal in the various subjects (Spearman rank correlation coefficient = 0.54; P less than 0.05). We conclude that aging is associated with a significant defect in the glucose transport system in isolated adipocytes, which may account for the post-receptor defect in in vivo insulin action in aging.

3-O-Methylglucose↗
PubMed1983

Persistent, tolerant or subacute infection in Borna disease virus-infected rats.

The rabbit-adapted Borna disease (BD) virus strain V was passaged by intracerebral infection of 1-day-old Wistar rats. Infectivity titres reached 10(8) infectious units per gram of brain 4 weeks after infection. No clinical signs were evident. The persistent infection could be induced with adapted or field strains of BD virus. Strains were identified by neutralization tests. The virulence of the rabbit-adapted BD virus for the rat increased with rat passages. The 5th passage induced clinical symptoms in animals infected at 1 week of age or older. Between 20% and 50% of diseased rats died. Virus-specific antigen was detectable immunohistologically in neurons of rats infected at all ages. Animals inoculated at 1 or 2 months of age, but not the neonatal rats, showed signs of inflammation in the brain. Infected rats produced specific antibodies. In the older groups (infected at ages of 1 or 2 months), and especially in surviving animals, occasionally, neutralizing antibodies with high titres were found. Transfer of primed spleen cells resulted in subacute disease. These findings demonstrate that neonatal rats can acquire a persistent, tolerant infection and that expression of disease is mediated by immunological factors.

Animals↗
PubMed1983

Insulin treatment reverses the postreceptor defect in adipocyte 3-O-methylglucose transport in type II diabetes mellitus.

The insulin resistance of type II diabetes mellitus is due to both receptor and postreceptor defects of in vivo insulin action, with the postreceptor defect being the predominant abnormality. Diminished glucose transport has been found in adipocytes from patients with type II diabetes, suggesting that decreased cellular glucose transport activity may be responsible in part for the in vivo postreceptor defect observed in these patients. Recent studies have shown that the in vivo postreceptor defect initially present in patients with Type II diabetes is significantly reversed by insulin therapy. For these reasons, we speculated that the defect in adipocyte glucose transport might also be corrected with exogenous insulin therapy. Therefore, we measured adipocyte 3-O-methylglucose transport in cells from five type II diabetic subjects before and after a 2-week period of intensive insulin treatment. Glycemic control was significantly improved by this regimen. The mean (+/- SE) fasting serum glucose level fell from 292 +/- 24 to 135 +/- 29 mg/100 ml (P less than 0.005), and the mean integrated glucose area under a 7-h meal tolerance test curve decreased from 171,212 +/- 20,403 to 72,408 +/- 9,292 mg/min . dl. The mean 3-O-methylglucose transport activity increased after treatment at all insulin concentrations studied, including basal (before, 0.18 +/- 0.05; after, 0.45 +/- 0.09 pmol/2 X 10(5) cells . 10 sec; P less than 0.005) and maximally effective (25 ng/ml) insulin concentrations (before, 0.50 +/- 0.14; after, 1.32 +/- 0.30 pmol/2 X 10(5) cells . 10 sec; P less than 0.025), although the mean maximal glucose transport activity was still 25% decreased compared to normal values, indicating that a residual in vitro postreceptor defect remained. These results corresponded well with the degree of reversal (75%) of the in vivo postreceptor defect, as assessed by the euglycemic glucose clamp technique. These studies demonstrated that the decrease in adipocyte glucose transport activity in type II diabetes is practically reversible by intensive insulin therapy. This closely corresponds to the reversal by insulin therapy of the postreceptor defect expressed in vivo and provides further evidence that a cellular cause of the postreceptor defect in type II diabetes is a decrease in glucose transport system activity in the major insulin target tissues.

3-O-Methylglucose↗
PubMed1983

Insulin binding to erythrocytes incubated in vitro at physiological temperature.

We have investigated the previously described time-dependent increase in specific insulin binding to freshly isolated human erythrocytes incubated at 37 C. We found that at 37 C, specific insulin binding to erythrocytes rose to and remained at equilibrium for the first 90 min of incubation; thereafter, it rose in a rapid linear fashion, directly related to the increase in the degradation of unbound insulin and paralleling the intensity of visible hemolysis. The rise in specific binding was intensified by conditions in which hemolysis was enhanced and attenuated by conditions designed to limit hemolysis or by agents capable of inhibiting the degradation of insulin despite hemolysis. Thus, gentle handling of the cells prevents hemolysis, the degradation of insulin, and the increase in apparent insulin binding. Furthermore, 5% albumin, 2.5 mM N-ethylmaleimide, or excess unlabeled insulin (100 micrograms/ml) inhibited insulin degradation (even in the presence of hemolysis) and prevented the rise in insulin binding. The rise in cell-associated radioactivity after 90 min of incubation at 37 C was due to cellular uptake of products of insulin degradation, since degraded [125I]insulin rapidly associated with freshly prepared erythrocytes. Acid extraction studies suggested that about 60% of the cell-associated degraded material was intracellular, while the remaining approximately 40% was bound to the cell surface. The data suggest that the rise in binding in erythrocytes incubated at 37 C is a result of insulin degradation products which associate with the cells. The generation of degraded insulin is due to hemolysate released from leaky cells, and this phenomenon is unique to the in vitro situation.

Adult↗
PubMed1978

Value of acid metabolic products in identification of certain corynebacteria.

Acid metabolic products of 23 strains of human and animal pathogenic corynebacteria, representing eight different species, were determined by gas chromatography. The results showed that the species examined were metabolically heterogeneous and could be presumptively identified based on the acid products produced. Corynebacterium equi did not produce any acids; C. renale produced lactate; and C. pyogenes produced major amounts of lactate, variable amounts of acetate, and minor amounts of succinate and pyruvate. C. kutscheri produced propionate and lactate as major products and pyruvate and oxalacetate as minor products. C. diphtheriae and C. pseudotuberculosis produced major amounts of propionate, acetate, and formate. In addition, C. pseudotuberculosis produced major amounts of pyruvate and minor amounts of succinate, lactate, and oxalacetate, whereas C. diphtheriae strains produced minor but variable amounts of lactate, succinate, fumarate, pyruvate, and oxalacetate. C. bovis produced aicd products similar to those of C. pyogenes but was readily distinguishable from the latter by the lack of hemolysis on blood agar, colony morphology, catalase reaction, and biochemicals. C. suis characteristically produced major amounts of ethanol, acetate, and formate and minor amounts of lactate and succinate but no propionate.

Carboxylic Acids↗