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Biomedical subjects

F M Matschinsky

Publications and source records attributed to F M Matschinsky.

At least 91 records · Page 5Linked to original sources
PubMed1988

Diabetes affects sorbitol and myo-inositol levels of neuroectodermal tissue during embryogenesis in rat.

ATP, ADP, phosphocreatine (PCr), creatine (Cr), glucose, malate, sorbitol, and myo-inositol (MI) were measured by quantitative histochemical techniques in pure neuroectodermal tissue of rat embryos of gestation days 11 and 12 that were dissected from normal and streptozocin-induced diabetic mothers. Neither gestational age nor maternal diabetes affected the tissue's energy potential (ATP-to-ADP and PCr-to-Cr ratios). Diabetes resulted in a fourfold rise in the embryonic glucose and a 25% increase in neuroectodermal malate content. Maternal hyperglycemia caused a rise in fetal sorbitol at days 11 and 12 of gestation. The MI content of the neuroectoderm was not affected by the maternal diabetic state in perfusion embryos (day 11); however, the near doubling of MI that occurs from day 11 to day 12 during normal development was prevented. Thus, embryos isolated from diabetic mothers on gestation day 12 had 30% less MI than embryos isolated from normal mothers. From these data we conclude that a rise in tissue sorbitol is not always accompanied by a fall in tissue MI. These results and recent information in the literature implicate involvement of decreased MI concentrations in the process leading to malformation of the nervous system in diabetic embryopathy.

Adenosine Diphosphate↗
PubMed1987

Cyclic AMP raises cytosolic Ca2+ and promotes Ca2+ influx in a clonal pancreatic beta-cell line (HIT T-15).

The effect on cytosolic Ca2+ concentration ([Ca2+]i) of cAMP analogues and the adenylate cyclase-stimulating agents forskolin, isoproterenol and glucagon has been examined in an insulin-secreting beta-cell line (HIT T-15) using fura 2. All these manipulations of the cAMP messenger system promoted a rise in [Ca2+]i which was blocked by the Ca2+ channel antagonists verapamil and nifedipine or by removal of extracellular Ca2+. The action of the adenylate cyclase activator forskolin was glucose-dependent. The results suggest that cAMP elevates [Ca2+]i in HIT cells by promoting Ca2+ entry through voltage-sensitive Ca2+ channels, not through mobilization of stored Ca2+. Activation of Ca2+ influx may be an important component of the mechanisms by which cAMP potentiates fuel-induced insulin release.

Animals↗
PubMed1987

HPLC analysis of nucleotide profiles in glucose-stimulated perifused rat islets.

Nucleotide concentrations were measured in isolated pancreatic islets from rats using HPLC. This method was used to study the role of nucleotides in islets, which were perifused for several hours with different substrates and exhibited signs of exhaustion. Using islet tissue extracts, it was possible to determine 11 nucleotides. It was hoped that alterations in islet nucleotide concentrations would provide clues for the biochemical basis for the exhaustion phenomenon; however, changes in nucleotide concentrations that were observed in exhausted islet tissue did not correlate with corresponding changes in insulin release. Therefore, they are unlikely to be directly related to islet exhaustion.

Animals↗
PubMed1987

Immunocytochemical and quantitative studies of Na+,K+-ATPase distribution in the developing chick cochlea.

Immunocytochemical methods were used to examine cryosections of the embryonic and neonatal chicken cochlea in order to study the histological distribution of the Na+,K+-ATPase molecule during maturation. In complementary studies the Na+,K+-ATPase capacity of microdissected freeze-dried substructures of the cochlea was determined fluorometrically. The dark cell of the tegmentum vasculosum exhibited intense immunochemical staining of the convoluted basolateral infoldings. The adjacent light cells demonstrated very little staining. The plasma membrane of the hair cell was also stained as were the first order auditory neurons, including the cell soma. The homogene cells and the supporting cells were unstained. The dark cell was only lightly stained with the antibody at stage 45 but became more intense and selective by the seventh postnatal day. The other cells of the cochlear duct exhibited specific immunofluorescent staining of their plasma membranes from stage 45 onwards and the fluorescent intensity did not change. The tegmentum vasculosum exhibited very high activities of the Na+,K+-ATPase enzyme relative to the other structures of the cochlea. Furthermore, a pronounced gradient of enzymatic activity was detected longitudinally. The proximal tip (or high-frequency end) had a sixteen-fold greater capacity for Na+- and K+-dependent ATP hydrolysis relative to the distal tip (or low-frequency end). The appearance of this enzyme in the tegmentum vasculosum during the development of the cochlea paralleled the known rate of improvement in hearing thresholds.

Animals↗
PubMed1987

Metabolism and electrophysiology in subendocardial Purkinje fibers after infarction.

Subendocardial Purkinje fibers (SEPF) have been implicated in the genesis of fatal arrhythmias that occur 24-48 h after infarction but little is known about the metabolic processes involved. Quantitative microchemical and electrophysiological studies were performed on normal and infarcted hearts removed 24 h after coronary artery occlusion. ATP, ADP, AMP, total adenine nucleotide content, phosphocreatine (PCr), and inorganic phosphate in superficial subendocardial Purkinje fibers from infarct preparations decreased approximately 30% compared with normal preparations. The phosphate potential decreased 45% in the infarct group. Similar changes were observed in adjacent contractile muscle between normals and infarcts. Action potentials of SEPF from infarct hearts had increased automaticity, markedly prolonged action potential durations at 50 and 90% repolarization (APD50 or APD90), but unchanged resting membrane potentials. The decrease in ATP, total adenine nucleotides, and the phosphate potential correlated linearly with APD50 and APD90. No correlation was found between PCr and APD90. This combined biochemical and electrophysiological approach provides a promising new way to further probe the biochemical basis of the abnormal electrical properties of subendocardial Purkinje fibers after myocardial infarction.

Action Potentials↗
PubMed1987

Glucokinase in B-cell-depleted islets of Langerhans.

Glucose phosphorylation was studied in B-cell-enriched or in B-cell-depleted pancreatic islets from normal or streptozotocin-diabetic rats, respectively, using quantitative histochemical procedures. The data indicate that B-cell-enriched preparations from normal animals and whole islets from normals, diabetics, and insulin-treated diabetic animals have comparable glucokinase activities. Average maximum velocities were (mmol/kg dry tissue/hr) 134.1 +/- 7.3 for whole islets and 125.6 +/- 10.7 for the B-cell-enriched preparations from normal rats, 143.1 +/- 13.6 for B-cell-depleted islets from diabetic rats, and 124.4 +/- 10.7 for B-cell-depleted islets from insulin-treated diabetic animals. The Kmax for glucose of the enzyme in islets from untreated diabetic rats was 16 mM, comparable to the Kmax found for glucokinase from normal rat islets. Mannoheptulose, previously shown to be a competitive inhibitor of glucokinase from liver and normal islets, also inhibited glucokinase in B-cell-depleted islets from diabetic rats. The data indicate that glucokinase is not selectively located in the B-cell, as was previously assumed, but is also found in A- and/or D-cells of diabetic rats. This observation raises significant questions about the functional role of islet glucokinase under control and diabetic conditions.

Animals↗
PubMed1987

Fuel-stimulated insulin secretion by clonal hamster beta-cell line HIT T-15.

Insulin secretion by monolayer cultures of HIT T-15 cells was measured in response to various fuel molecules (glucose, dihydroxyacetone, lactate, glutamine, alpha-ketoisocaproic acid, alpha-ketoisovaleric acid) and a nonmetabolized glucose analogue (3-O-methylglucose). HIT cells secreted insulin in response to fuel molecules, but 3-O-methylglucose was ineffective. Stimulation of insulin release by fuels was increased by isobutylmethylxanthine and blocked by antimycin A. Iodoacetate selectively inhibited glucose-stimulated insulin release but had little effect on alpha-ketoisocaproic acid-stimulated insulin secretion. These results indicate that HIT cells retain the capacity of normal beta-cells to act as fuel sensors. Thus, HIT cells may provide a well-defined and relatively abundant tissue source in studies of stimulus-secretion coupling in beta-cells stimulated by fuels.

3-O-Methylglucose↗
PubMed1986

Acetylcholine stimulates glucose metabolism by pancreatic islets.

Acetylcholine stimulates insulin secretion in the presence of physiological concentrations of glucose. Stimulation of insulin secretion by acetylcholine is accompanied by an increase in glucose usage by isolated rat islets. Acetylcholine increased glucose usage by 38%, 28%, and 12% at 3.5 mM, 5.5 mM, and 10 mM glucose, respectively, compared to glucose usage by isolated islets incubated with glucose alone. Data showing increased glucose usage in islets treated with acetylcholine converge with data from an earlier report (J. Biol. Chem. 254 3921-3929 [1979]) showing a crossover point for glycolytic metabolites at phosphofructokinase to indicate that activation of glycolysis by acetylcholine results from increased phosphofructokinase activity and coordinate activation of hexokinase in intact islets.

Acetylcholine↗
PubMed1986

Metabolic concomitants in pure, pancreatic beta cells during glucose-stimulated insulin secretion.

The role of the redox potential in insulin secretion by beta cells stimulated with high glucose was investigated using an in vitro pancreas perfusion system. To assess glycolytic flux the sum of fructose-1,6-P2 + triose-P was determined in pure beta cells microdissected from lyophilized sections of the isolated perfused pancreas quick frozen during the early insulin secretory response. L-Glycerol 3-phosphate and dihydroxyacetone phosphate were measured as indicators of the free cytosolic [NAD+]/[NADH] ratio and NADH and NADPH were also measured. Fructose-1,6-P2 + triose-P was increased in beta cells simultaneously with the onset of insulin secretion indicating an increase in glucose metabolism had occurred. The ratio of [dihydroxyacetone phosphate]/[L-glycerol 3-phosphate] increased simultaneously with the onset of insulin secretion. NADH content increased only after initiation of insulin secretion and NADPH levels remained unchanged during the early secretory response to high glucose. These data contradict the hypothesis that insulin secretion is triggered by a more reduced cytosolic redox state and instead indicate that insulin secretion is initiated by other metabolic coupling factor(s) generated in beta cells stimulated by high glucose.

Animals↗
PubMed1986

Differential regulation of glucokinase activity in pancreatic islets and liver of the rat.

The differential tissue-specific regulation of glucokinase activity in liver and pancreatic islet cells was investigated in the insulinoma-bearing rat. A transplantable insulinoma caused hyperinsulinemia and hypoglycemia in the host by 2-3 months after implantation. Suppression of the pancreatic B-cells by the high insulin and/or low glucose manifested itself by a decrease of insulin in islet tissue. Removal of the tumor initiated transient insulin deficiency and hyperglycemia with extremes of these changes at 24 h after tumor resection. These conditions markedly affected glucose phosphorylation in the islet cells: glucokinase activity was reduced 71% in islet samples from insulinoma-bearing rats, and the enzyme fully recovered within 24 h after tumor resection. Hexokinase activity, by contrast, was not affected by these manipulations. To evaluate the relative contributions of hypoglycemia and hyperinsulinemia in islet glucokinase adaptation, glucose was intravenously infused to insulinoma-bearing rats; glycemia in excess of 150 mg/100 ml combined with excessive hyperinsulinemia resulted in a partial recovery of islet glucokinase activity, first apparent after 9 h of glucose infusion and with doubling of the activity after 24 h after glucose loading. In contrast, liver glucokinase was increased nearly 4-fold at the time of extreme hypoglycemia and hyperinsulinemia and rapidly fell to control rates following tumor removal. Intravenous infusion of glucose for 24 h into the tumor-bearing rat (i.e. hyperglycemia combined with excessive plasma insulin) had no influence on liver glucokinase activity. Liver hexokinase was not influenced by any of these experimental manipulations. The data indicate that the activities of pancreatic islet and liver glucokinase are regulated in a differential manner. Insulin is apparently the primary determinant of liver glucokinase and glucose seems to control islet glucokinase. Biochemical mechanisms for differential organ-specific regulation of glucokinase activity seem to have evolved such that this enzyme may play a dual role in glucose homeostasis, namely to serve as insulin-dependent glucose sensor in the B-cells and as insulin-sensitive determinant of hepatic glucose use.

Adenoma, Islet Cell↗
PubMed1986

Altered retinal metabolism in diabetes. II. Measurement of sodium-potassium ATPase and total sodium and potassium in individual retinal layers.

Pathological changes in retinas of diabetics include specific morphological, biochemical, and functional abnormalities. As biochemical manifestations of the disease, increased sorbitol and decreased myo-inositol were found in retinas of experimentally diabetic animals. Similar alterations in polyol metabolism have been associated in nerves of diabetics with a reduction of Na+-K+-ATPase activity. To determine whether this association extends to the retinas of diabetic animals, we applied quantitative histochemical techniques to measure ATPase activities and the amounts of sodium and potassium in samples from nine individual layers of cryostat sections of rabbit retina. ATPase activities were determined fluorimetrically, and the ions were measured by atomic absorption with a carbon rod atomizer. The activity of Na+-K+-ATPase was reduced in the retinal pigmented epithelium (retinal pigment epithelium) and in selected layers of the neural retina, and total sodium in the retinal pigment epithelium layer was elevated in diabetes. The retinal pigment epithelium forms the outer component of the blood-retinal barrier and partly determines the composition of the retinal interstitial fluid. Changes in retinal pigment epithelium biochemistry and function might alter the intraretinal environment, predisposing neural retina or retinal blood vessels to disease. The morphologically and functionally well defined retinal pigment epithelium may provide a useful model for studying the pathogenesis of diabetic complications.

Animals↗
PubMed1986

Altered retinal metabolism in diabetes. I. Microanalysis of lipid, glucose, sorbitol, and myo-inositol in the choroid and in the individual layers of the rabbit retina.

Total lipid, sucrose, glucose, sorbitol and myo-inositol contents in individual layers from normal and alloxan-diabetic rabbit retinas were measured using gravimetric and enzymatic microtechniques. Pure samples of nine retinal layers were microdissected from freeze-dried retinal cryosections. The lipid content was measured by loss of weight after ethanol and hexane extraction. Retinal lipid varied 3-fold across the retina and was not influenced by diabetes. Sucrose, glucose, sorbitol, and myo-inositol were measured with fluorimetric microassays. Sucrose infused intravenously prior to sampling the tissue did not traverse the outer blood retinal barrier of the normal or the diabetic retina. In both normals and diabetics, glucose followed a diffusional curve, with outer and inner retinal concentrations, respectively, equal to choroidal blood and vitreal glucose concentrations. Sorbitol was elevated in all retinal layers of diabetic animals. The peak sorbitol concentrations, of 2 mmol/kg defatted dry weight in diabetics, were not high enough to be osmotically significant. Retinal myo-inositol, of the order found in brain tissue (10-30 mmol/kg defatted dry tissue), was decreased by 22-40% in all retinal layers of the diabetics. The results indicate that diabetes affects the metabolism of retinal structures independently of the small blood vessel disease that is the hallmark of diabetes of long duration. It is conceivable that primary intraretinal metabolic alterations cause, aggravate, or perpetuate the well known degenerative processes that occur in retinal blood vessels in diabetes.

Animals↗
PubMed1986

Neomycin: a specific drug to study the inositol-phospholipid signalling system?

Neomycin, an antibiotic previously thought to interact specifically with inositol-containing phospholipids, was found to inhibit IP3-mediated Ca2+ release from the intracellular stores of permeabilized insulinoma and liver cells. This inhibition could be relieved by increasing the IP3 concentration. Radiolabelled IP3 was found to bind tightly to columns prepared from neomycin covalently attached to glass beads. ATP was also bound by these columns. It is concluded that neomycin acts in biological systems as a weak anion exchanger and is therefore unsuitable for use as a specific tool to study the role of inositol phospholipids in intracellular signalling.

Animals↗
PubMed1986

Experimental diabetes mellitus impairs the function of the retinal pigmented epithelium.

The retinal pigmented epithelium (RPE), which influences the composition of the retinal extracellular fluid, is significantly affected in diabetes. Changes in RPE morphology, permeability, and electrophysiology in experimentally diabetic animals have been described. To facilitate the study of diabetes-related changes in RPE metabolism, we applied the techniques of quantitative histochemistry to pure samples of RPE and individual retinal layers from eyes of normal and alloxan-diabetic rabbits. Glucose within the RPE approximated serum levels in both normal and diabetic animals. Other changes in diabetics included increased sorbitol, decreased myo-inositol, elevated total Na, and loss of measurable Na+-K+-ATPase activity within the RPE. The altered ion metabolism was associated with a progressive decrease in the amplitude of the RPE-generated c-wave of the electroretinogram. The deterioration of the c-wave was arrested by treatment of the diabetic animals with either myo-inositol supplementation or with sorbinil, an inhibitor of aldose reduction. Diabetic alterations in the RPE might impair the ability of the tissue to maintain normal transport functions. The subsequently altered composition of the extracellular environment of the retina may play an important role in the pathogenesis of diabetic retinopathy.

Animals↗