Biomedical subjects

F M Matschinsky

Publications and source records attributed to F M Matschinsky.

At least 73 records · Page 4Linked to original sources

PubMed1991

Effect of linogliride on hormone release from perfused rat pancreas. Fuel dependence and desensitization by tolbutamide.

We examined the effect of the hypoglycemic drug linogliride on hormone release from the in vitro perfused rat pancreas. Linogliride stimulated insulin release in the absence of glucose either in the presence or absence of a physiological mixture of amino acids. In addition, linogliride inhibited amino acid-induced glucagon release. Half-maximal effects of linogliride on insulin and glucagon release were achieved at concentrations as low as 26 and 3 microM, respectively. The effects of linogliride on hormone release largely resembled those of tolbutamide. In the absence of amino acids, the stimulation of insulin release by linogliride or tolbutamide was transient. When the pancreas had been preperfused for 20 min with tolbutamide, linogliride no longer had an effect on hormone release. Likewise, tolbutamide remained without effect in pancreases preperfused with linogliride. These data suggest that linogliride and tolbutamide may have a similar mechanism of action.

Amino Acids↗

PubMed1990

Glucose regulates glucokinase activity in cultured islets from rat pancreas.

In this study, we have used isolated pancreatic islets cultured for 7 days in 3 or 30 mM glucose to explore whether glucokinase is induced or activated by high glucose concentrations and has related enzyme activity to glucose-stimulated insulin release. Islets cultured in low glucose medium or low glucose medium plus 350 ng/ml insulin did not respond to high glucose stimulation. Islets cultured in medium containing high glucose concentrations showed a high rate of basal insulin secretion when perifused with 5 mM glucose, and the insulin release was greatly augmented in a biphasic secretion profile when the glucose concentration was raised to 16 mM. Islet glucokinase and hexokinase activities were determined by a sensitive and specific fluorometric method. Glucokinase activity was reduced to approximately 50% in islets cultured in low glucose medium with or without insulin present compared to results with fresh islets. However, islets cultured in 30 mM glucose showed that glucokinase activity was elevated to 236% compared to results with fresh islets. It is concluded that (a) glucose is the physiological regulator of glucokinase in the islet of Langerhans and that (b) the activity of glucokinase plays a crucial role in glucose-induced insulin secretion.

Animals↗

PubMed1990

Plasma from BB/Wor rats increases insulin secretion by perfused rat pancreas.

Diabetes-prone (DP) BB rats develop spontaneous autoimmune diabetes mellitus in the context of multiple abnormalities of humoral and cellular immunity. Diabetes-resistant (DR) BB rats have phenotypically normal immune systems and rarely become spontaneously hyperglycemic, but can be rendered diabetic by in vivo immune elimination of T cells that express the RT6 surface alloantigen. To determine if humoral factors in these animals influence beta-cell function, we studied the effect of BB rat plasma on glucose-induced insulin secretion from the isolated perfused rat pancreas. We found that plasma dialyzed to remove molecules less than 14 kD from nondiabetic DR and DP BB rats significantly enhanced total insulin secretion [4806 +/- 711 ng (+/- SEM; n = 6) and 4968 +/- 1235 ng (n = 7), respectively] from perfused pancreata when compared with the effects of either plasma from Wistar-Furth rats (2585 +/- 336 ng; n = 9) or medium containing no plasma (1862 +/- 92 ng; n = 38). The presence of chemically induced diabetes was also associated with enhanced insulin secretion [3276 +/- 414 ng (n = 8) using alloxan and 3956 +/- 470 ng (n = 7) using streptozocin], but the greatest degree of enhancement was observed with plasma from spontaneously diabetic BB rats (6521 +/- 751 ng; n = 17). The enhancement of insulin secretion by BB rat plasma, both diabetic and nondiabetic (DR and DP), was characterized by preservation of first and second phase hormone release. Heat inactivation of acutely diabetic BB rat plasma did not affect its ability to stimulate insulin secretion. We conclude that the plasma of BB rats, both before and after the onset of autoimmune diabetes mellitus, contains a factor other than complement of greater than or equal to 14 kD that enhances insulin secretion in vitro from the isolated perfused pancreas.

Animals↗

PubMed1990

Diabetes and the myo-inositol paradox.

To test the general applicability of the hypothesis that diabetes mellitus causes increased polyol pathway activity, decreased tissue free myo-inositol, and resultant pathological changes in tissues susceptible to the ravages of diabetes, we measured glucose, sorbitol, and myo-inositol with quantitative histochemical techniques in layers of the cornea, the aortic myointima, the cardiac left ventricle and atrioventricular node (AVN), and retina and kidney after 19 days or 2 mo (mildly diabetic non-insulin-treated [MD] and severely diabetic insulin-treated [SD] groups) in the alloxan-induced diabetes model. In the aqueous humor, glucose rose linearly with increased serum glucose, sorbitol was markedly increased in the MD and SD groups, and myo-inositol did not change in any diabetic group. There was no change in glucose or sorbitol in aortic myointima in any group, but myoinositol was decreased in 19-day diabetic rabbits by 26%, unchanged in MD rabbits but paradoxically increased by 60% in SD rabbits. Glucose, sorbitol, and myo-inositol increased in all three corneal layers in SD rabbits but only in epithelium and stroma in 19-day and MD rabbits. AVN glucose and sorbitol did not change in 19-day diabetic, MD, or SD diabetic rabbits. AVN myo-inositol was three times higher than ventricular myo-inositol and did not appear to change in SD rabbits. Retinal pigmented epithelium myo-inositol was decreased 30% in SD rabbits. Glomerular myo-inositol was also decreased, but not significantly, in SD rabbits. We conclude that the paradoxical increase in corneal and aortal myo-inositol raises fundamental questions about the general applicability of the myo-inositol-depletion hypothesis.

Animals↗

PubMed1990

Glucokinase as glucose sensor and metabolic signal generator in pancreatic beta-cells and hepatocytes.

This article reviews evidence for a pivotal role of glucokinase as glucose sensor of the pancreatic beta-cells. Glucokinase explains the capacity, hexose specificity, affinities, sigmoidicity, and anomeric preference of pancreatic islet glycolysis, and because stimulation of glucose metabolism is a prerequisite of glucose stimulation of insulin release, glucokinase also explains many characteristics of this beta-cell function. Glucokinase of the beta-cell is induced or activated by glucose in contrast to liver glucokinase, which is regulated by insulin. Tissue-specific regulation corresponds with observations that liver and pancreatic beta-cell glucokinase are structurally distinct. Glucokinase could play a glucose-sensor role in hepatocytes as well, and certain forms of diabetes mellitus might be due to glucokinase deficiencies in pancreatic beta-cells, hepatocytes, or both.

Animals↗

PubMed1989

A role for malonyl-CoA in glucose-stimulated insulin secretion from clonal pancreatic beta-cells.

To gain insight into the relationship between acyl coenzyme A (CoA) esters and glucose-induced insulin release, acyl-CoA profiles were determined in clonal pancreatic beta-cells (HIT). A high sensitivity high performance liquid chromatography method was used to measure malonyl, succinyl, beta-hydroxy beta-methylglutaryl and acetyl-CoA esters and free CoASH. Malonyl-CoA content increased more than 3-fold following exposure of HIT cells to 10 mM glucose. The rise in malonyl-CoA, which preceded insulin secretion, was evident 2 min after exposure to glucose and was sustained for at least 30 min. The increase in malonyl-CoA was associated with inhibition of fatty acid oxidation, increased de novo lipid synthesis and a rise in diacylglycerol content. Succinyl-CoA levels, which may reflect anaplerotic influx into the citric acid cycle, were elevated in the presence of glucose. The concentration of acetyl-CoA and the ratio of free CoASH to acetyl-CoA was unchanged. The data are consistent with a metabolic model in which malonyl-CoA mediates the switch from fatty acid catabolism to lipid synthesis during glucose stimulation of beta-cells. We suggest that these changes in lipid metabolism, by leading to increased diacylglycerol synthesis or protein acylation could play a pivotal role in the regulation of the sustained phase of insulin secretion.

Acyl Coenzyme A↗

PubMed1989

Selective activation of Ca2+ influx by extracellular ATP in a pancreatic beta-cell line (HIT).

The action of exogenous ATP on cytoplasmic free Ca2+ ([Ca2+]i) was studied in insulin secreting cells using fura-2. Stimulation of clonal pancreatic beta-cells (HIT) with ATP (range 2-20 microM) evoked a sustained elevation in [Ca2+]i. ATP selectively promoted Ca2+ influx and not Ca2+ mobilization since (1) the effect required external Ca1+ and (2) was observed in cells in which internal stores were depleted with ionomycin (3) the rate of Mn2+ influx, measured as the quenching of the fura-2 signal, was accelerated by ATP. The action of ATP was unaffected by the voltage-sensitive Ca2+ channel blockers nifedipine and verapamil as well as by a depolarizing concentration of K+. The effect on [Ca2+]i was highly specific for ATP since AMP, ADP, adenosine 5'-[gamma-thio]triphosphate, adenosine 5'-[beta, gamma-methylene]triphosphate, GTP and adenosine were ineffective. In normal pancreatic islet cells, both exogenous ATP (range 0.2-2 microM) and ADP induced a transient Ca2+ elevation that did not require external Ca2+. The nucleotide specificity of the effect on [Ca2+]i suggests that ATP activates P2 gamma purinergic receptors in normal beta-cells. Thus, ATP evokes a Ca2+ signal in clonal HIT cells and normal islet cells by different transducing systems involving distinct purinoreceptors. A novel mechanism for increasing [Ca2+]i by extracellular ATP is reported in HIT cells, since the nucleotide specificity and the selective activation of Ca2+ influx without mobilization of internal Ca2+ stores cannot be explained by mechanisms already described in other cell systems.

Adenine Nucleotides↗

PubMed1989

Biochemical manifestations of diabetes mellitus in microscopic layers of the cornea and retina.

Biochemical evidence of glucose toxicity was found in the retinal and corneal layers of diabetic rabbits. It can be reasonably assumed that the observed changes are causally related to the morphological and physiological diabetic pathologies of the retinal and corneal cells. Intracellular glucose is greatly increased, and the polyol pathway activity appears to be enhanced, resulting in an accumulation of intracellular sorbitol, which can be assumed to be oxidized to fructose. Accompanying the alterations of glucose metabolism are disturbances in myoinositol and Na+ handling by the affected structures. The detailed relationship of the observed metabolic effects of hyperglycemia to changes in cellular ion handling and the observed morphological and functional disturbances has yet to be elucidated. The morphologically and functionally discrete populations of RPE and CEN cells, which are readily amenable to experimental manipulation in situ and in cell culture may serve as unique models for systematic examination of the causes and the consequences of diabetes leading to ocular complications in particular and to the complications of other more complex tissues such as nerve and kidney. The present data show that the findings in one population of cells may not be completely reproducible in another as can be seen in the diverse myoinositol responses of the retinal and corneal layers to diabetes mellitus. The diverse responses perhaps reflect unique adaptive capabilities of individual tissues to the diabetic condition. It is a challenge for complications research to fully appreciate diverse responses of various tissues to persistent glucose intoxication and to delineate meticulously the time courses of such heterogeneous responses, which might result in debilitating pathology in certain cases but in a compensated chronic disease state in others. The corneal endothelium and the RPE are relatively resilient structures compared with the mural and endothelial cells of the retinal microvessels which are destroyed by the diabetic condition. Factors and components that protect tissues against the persistent effects of hyperglycemia need to be uncovered. Success in such an endeavor could be of benefit in the management of diabetic complications.

Animals↗

PubMed1989

Functional pancreatic beta-cell line from SV40 T-antigen transgenic mouse.

Cell line IgSV195, derived from a pancreatic tumor that arose in an SV40 T-antigen transgenic mouse, retains certain morphological and physiological characteristics of pancreatic beta-cells throughout in vitro and in vivo passage. Insulin secretion is stimulated by exposure of these cells to fetal bovine serum and a combination of 3-isobutyl-1-methylxanthine and glutamine but not by concentrations of glucose in the physiological range. Insulin processing appears to be intact. Neither class I nor class II major histocompatibility complex (MHC) antigens are routinely expressed at the cell surface; however, MHC class I--but not class II--encoded gene products are detected after treatment with recombinant interferon-gamma (IFN-gamma) alone or in combination with tumor necrosis factor. Cytolysis of IgSV195 cells by SV40 T-antigen-specific H-2b-restricted lymphocytes is similarly dependent on IFN-gamma pretreatment. These results emphasize that SV40 T-antigen transgenic mice are likely sources of cell lines that retain their differentiated function in vitro. The IgSV195 cell line provides an accessible model in which to investigate the control of gene expression and function of pancreatic beta-cells.

Animals↗

PubMed1989

Pyridine nucleotides and phosphorylation potential of rabbit corneal epithelium and endothelium.

In order to validate in situ corneal redox fluorometry, the redox state and phosphorylation potential of freeze trapped rabbit corneal epithelium and endothelium were studied using quantitative histochemical methods. The results were compared with noninvasive measurements using an optically sectioning fluorometer microscope. Enucleated rabbit eyes were either frozen in Freon-12, cooled by liquid nitrogen or exposed for 1 hr in 1 mM NaCN to block oxidation and then freeze trapped. Corneas were sectioned, freeze-dried, samples of individual layers dissected, weighed, and analyzed for: NADH, NAD+, NADPH, NADP+, ATP, ADP, and Pi. The aerobic epithelium showed a ratio for NAD+/NADH of 1.85 +/- 0.08 (9). In anoxia this ratio decreased to 1.06 +/- 0.07 (8). The NAD+/NADH ratio of aerobic endothelium was 3.25 +/- 0.28 (6); in anoxia this ratio was 0.68 +/- 0.14 (5). The values of phosphorylation potential ATP/(ADP X Pi)M-1 were: 447.9 +/- 40.2 (9) in aerobic epithelium, 378.2 +/- 24.7 (5) in anoxic epithelium; 308.4 +/- 25.2 (7) in aerobic endothelium and 225.4 +/- 19.1 (5) in anoxic endothelium. Aerobic-anoxic transitions alter the concentrations of NADH and NAD+ but did not affect the concentration of NADPH and NADP+. The microhistochemical data indicate that the redox state of rabbit epithelium is less sensitive to hypoxia than the endothelium. This difference between the two limiting layers is reflected in alterations of phosphorylation potential induced by hypoxia. The similarly high efficiencies of both layers in maintaining relatively high ATP levels during histotoxic hypoxia is most likely a result of compensatory ATP generation by enhanced glycolysis.

Adenine Nucleotides↗

PubMed1988

Cell-specific patterns of oscillating free Ca2+ in carbamylcholine-stimulated insulinoma cells.

The effect of the muscarinic agonist carbamylcholine on cytoplasmic Ca2+ concentration ([Ca2+]i was examined at the single cell level in clonal pancreatic beta-cells (HIT). Cells were loaded with the indicator dye fura 2, and [Ca2+]i was measured by microfluorimetry. Carbamylcholine induced changes in Ca2+ that differed from cell to cell and provoked in some cells oscillatory Ca2+ fluctuations. During a transient, free Ca2+ rose to a peak within 1-3 s. The frequency of the oscillations increased with agonist concentration. Oscillations in [Ca2+]i occurred in the absence of external Ca2+. When cells were perifused for a sufficient period of time without carbamylcholine, near identical Ca2+ responses were elicited in each cell by successive applications of the agonist. Thus, individual cells displayed characteristic and reproducible Ca2+ responses with respect to amplitude, frequency, and shape of the transients as well as latency in onset of the initial Ca2+ rise. We propose that the biological response to a Ca2+ agonist in a given cell is not only determined by the frequency and amplitude of Ca2+ oscillations but is governed by the unique pattern of the Ca2+ signal of each cell, which may be termed "Ca2+ fingerprint."

Adenoma, Islet Cell↗

PubMed1988

Regulation of steady-state free Ca2+ levels by the ATP/ADP ratio and orthophosphate in permeabilized RINm5F insulinoma cells.

Stimulation of insulin secretion in the pancreatic beta-cell by a fuel such as glucose requires the metabolism of the fuel and is accompanied by increases in oxygen consumption and intracellular free Ca2+. A very early signal for these events could be a decrease in the cytosolic ATP/ADP ratio due to fuel phosphorylation. To test this hypothesis the regulation of free Ca2+ was evaluated in permeabilized RINm5F insulinoma cells that sequester Ca2+ and maintain a low medium free Ca2+ concentration (set point), between 100 and 200 nM, in the presence of Mg2+ and ATP. ATP, creatine, creatine phosphate, and creatine phosphokinase were added to the media to achieve various constant ratios of ATP/ADP. Free Ca2 was monitored using fura-2. The results demonstrated that the steady-state free Ca2+ concentration varied inversely with the ATP/ADP ratio and orthophosphate (Pi) levels. In contrast, no correlation between free Ca2+ and the phosphorylation potential (ATP/ADP.Pi) was found. Regulation of the Ca2+ set point by the ATP/ADP ratio was observed at ratios between 5 and 50 and at Pi concentrations between 1 and 7 mM, irrespective of whether mitochondria were participating in Ca2+ sequestration or were inhibited. Increasing the ATP/ADP ratio stimulated Ca2+ uptake by the nonmitochondrial pool but did not modify Ca2+ efflux. Glucose 6-phosphate (1 mM) had no effect on the Ca2+ set point. The data suggest that variations in the cytosolic ATP/ADP ratio induced by fuel stimuli may regulate Ca2+ cycling across nonmitochondrial compartments and the plasma membrane by modulating the activity of Ca2+ -ATPases. A mechanism linking fuel metabolism and cytosolic ATP/ADP ratio to activation of the Ca2+ messenger system in pancreatic beta-cells is proposed.

Adenoma, Islet Cell↗

PubMed1988

Linked oscillations of free Ca2+ and the ATP/ADP ratio in permeabilized RINm5F insulinoma cells supplemented with a glycolyzing cell-free muscle extract.

We show in the accompanying paper that the steady-state level of free Ca2+ maintained by the organelles of permeabilized RINm5F insulinoma cells varies inversely with the ATP/ADP ratio when this ratio is set by addition of creatine phosphokinase and fixed ratios of creatine to creatine phosphate. We, therefore, asked whether acute cyclic alterations in the cytosolic ATP/ADP ratio in the range known to modulate O2 consumption might be involved in regulating the physiological activity of Ca2+ -ATPases and the cytosolic free Ca2+ level. To explore this hypothesis we combined two experimental systems: 1) permeabilized RINm5F insulinoma cells that can maintain a low medium Ca2+ concentration and 2) a cell-free extract of rat skeletal muscle that spontaneously exhibits oscillatory behavior of glycolysis and linked oscillations in the ATP/ADP ratio, when provided with glucose. The free Ca2+ level maintained by the permeabilized cells oscillated in phase with the glycolytic oscillations and correlated closely with the ATP/ADP ratio but not with glucose 6-phosphate, fructose 6-phosphate, orthophosphate, or pH. When glucokinase replaced hexokinase as the glucose phosphorylating enzyme, Ca2+ oscillations were induced by increasing the glucose concentration from 2 to 8 mM. The results demonstrate a link between metabolite changes and free Ca2+ levels in a reconstituted physiological system. They support a model in which oscillations in glycolysis and the ATP/ADP ratio may cause oscillations in cytosolic free Ca2+, beta-cell electrical activity, and insulin release.

Adenoma, Islet Cell↗

PubMed1988

Characteristics of glucokinase of the Kirkman insulinoma.

It was investigated whether the well-known transplantable insulinoma of the hamster (the Kirkman tumor) contains glucokinase and if so, what its kinetic characteristics are, and whether its cellular levels might be regulated in a manner typical for islet tissue. The supernatant of tumor homogenates contained a low-affinity component (Km 9.7 mmol/L) of glucose phosphorylating activity, apparently glucokinase. Partially purified insulinoma glucokinase exhibited similar kinetic characteristics to liver glucokinase (Km for glucose 5.0 and 5.3 mmol/L, half-maximal saturation 6.9 and 6.3 mmol/L, Hill coefficient 1.63 and 1.62, Ki for mannoheptulose 0.9 and 0.6 mmol/L in hamster insulinoma glucokinase and hamster liver glucokinase, respectively). Insulinoma glucokinase activity was not affected by the age of the tumor. Tumor-bearing hamsters without further treatment stayed normoglycemic (172 +/- 9.5 mg/dL) for the duration of the experiment. Fasting caused hypoglycemia (49 +/- 5.0 mg/dL), and pretreatment with streptozotocin prior to tumor transplantation caused hyperglycemia (393 +/- 20.6 mg/dL) in the tumor-bearing hamsters. Blood glucose levels of the host hamsters did not affect the content of the insulinoma glucokinase (83 +/- 3.5 mU/g in hypoglycemic group, 88 +/- 9.0 mU/g in hyperglycemic group, and 86 +/- 3.5 mU/g in normoglycemic group). Thus, biosynthesis and degradation of insulinoma glucokinase does not seem to be regulated by glucose as found to be true for islet glucokinase. Since glucokinase is constitutively present, the stable transplantable Kirkman tumor could serve as a useful model for studying the pancreatic B-cell glycolysis system which is characterized by the presence of both hexokinase and glucokinase.

Adenoma, Islet Cell↗

PubMed1988

The 28-kDa calbindin-D is a major calcium-binding protein in the basilar papilla of the chick.

In previous work we identified a basilar papilla protein (BPP23) that appears to be one of the most abundant soluble proteins in the basilar papilla of the chick cochlea. Here we report the purification of protein BPP23 from chick cochlea and the generation of a specific antiserum. Immunoblotting and immunoprecipitation experiments with this antiserum indicate that BPP23 is a calcium-binding protein very similar, if not identical, to avian calbindin, the 28-kDa vitamin D-dependent calcium-binding protein. Although the basilar papilla contains both receptor hair cells and supporting cells, immunocytochemical studies by others have localized calbindin-like immunoreactivity to the hair cells in the rat auditory receptor epithelium. Our estimates of the abundance of protein BPP23, assuming exclusive localization within the hair cell, indicate a concentration of at least 1 mM. Avian calbindin has four high-affinity (Kd = 0.5 X 10(-6)) calcium-binding sites. The presence of a specific calcium-binding activity at such high levels suggests an important function for cochlear calbindin (BPP23) in hair cell calcium homeostasis and auditory transduction.

Animals↗

PubMed1988

Quantitative histochemical determination of Na+ and K+ in microscopic samples using carbon furnace atomic absorption spectrometry.

Carbon furnace atomic absorption spectrometry was used to measure the Na and K content of freeze-dried microscopic tissue samples. This method was sufficiently sensitive to measure pmol amounts of Na and K from tissue weighing 10-60 ng. Within the spatial resolution of the microdissection procedure, ion diffusion that might occur during cryosectioning, freeze-drying, and dissection of the tissue did not seem to be a problem. Data obtained with this methodology were in agreement with previously reported values of the Na and K content of various tissues, thus supporting the usefulness of this quantitative histochemical technique.

Animals↗

PubMed1988

Control of glucose metabolism in pancreatic beta-cells by glucokinase, hexokinase, and phosphofructokinase. Model study with cell lines derived from beta-cells.

Glucose usage by soluble fractions of cell extracts from two insulin-producing cell lines, RINm5F and HIT, was investigated. Analysis of enzyme activities indicated that glucose phosphorylation and phosphofructokinase are likely to be the rate-limiting steps of glycolysis in both RINm5F and HIT cell extracts. RINm5F extracts, which lack glucokinase, exhibited relatively flat concentration-dependency curves of glucose usage and showed substantial inhibition of hexokinase. HIT cell extracts, which contain glucokinase but lack hexokinase, exhibited sigmoidal concentration-dependency curves of glucose usage, reflecting almost fully expressed glucokinase activity. A reconstituted system prepared from RINm5F and HIT cell extracts exhibited a composite concentration-dependency curve of glucose usage and showed substantial inhibition of hexokinase and almost fully expressed glucokinase. However, conditions that activate phosphofructokinase, such as addition of ammonium sulfate or fructose 2,6-bisphosphate or alkalization, removed the inhibition of hexokinase without noticeably affecting the glucokinase component of usage. Results obtained with a reconstituted system containing RINm5F cell extract and purified glucokinase were consistent with these findings. The data presented here indicate that this reconstituted cell-free system serves as a valid model for the study of aspects of glycolytic control in the islet. This model illustrates the preeminent role of glucokinase in the control of glycolysis, consistent with its glucose-sensor function in the islet. In addition, these studies help to define the contribution of phosphofructokinase to the control of glycolysis and the mechanism whereby changes in phosphofructokinase activity could modulate, via changes in the glucose 6-phosphate concentration, the activity of hexokinase and hence the net glycolytic flux.

Ammonium Sulfate↗

PubMed1988

Control of glucose phosphorylation and glucose usage in clonal insulinoma cells.

Glucose metabolism was investigated in two established clonal insulinoma cell lines (RINm5F and HIT) and in a newly developed line of mouse insulinoma cells (IgSV195). The hexokinase capacity in the homogenates of RINm5F cells was 22.1 +/- 3.23 U/g protein, but glucokinase was barely detectable (0.06 +/- 0.013 U/g protein). In contrast, both HIT and IgSV195 cells contained glucokinase (1.5 +/- 0.17 and 1.0 +/- 0.16 U/g protein, respectively) in addition to hexokinase activity. Glucose usage by the intact cells qualitatively reflected the glucose phosphorylation found in the cell-free extracts. RINm5F cells exhibited a high glucose usage rate with one high-affinity component, whereas both HIT and IgSV195 cells showed two components with different glucose affinities. HIT and IgSV195 cells may be useful for a model of pancreatic beta-cell glycolysis.

Adenoma, Islet Cell↗