PubMed Health⌕ Search

Biomedical subjects

B Draznin

Publications and source records attributed to B Draznin.

At least 55 records · Page 3Linked to original sources
PubMed1994

Evidence that p21ras mediates the neurotrophic effects of insulin and insulin-like growth factor I in chick forebrain neurons.

Insulin and insulin-like growth factors (IGF-I and IGF-II) support the survival and differentiation of many types of neurons, including those from fetal chick forebrain. The mechanisms by which these peptides exert their neurotrophic actions are poorly understood. The aims of this study were to determine if insulin and IGF-I activate p21ras in fetal chick forebrain neurons and if activation of p21ras mediates the neurotrophic actions of these peptides. Activation of neuronal p21ras was examined by measuring the amount of GTP bound to p21ras before and after growth factor treatment. Insulin and IGF-I increased the ratio of GTP/GTP + GDP by 31 +/- 9.0% and 36 +/- 8.0%, respectively, p21Ras activation by insulin and IGF-I was maximal within 5 min. In the presence of insulin the response was sustained out to 180 min, whereas the response to IGF-I decreased significantly by 180 min. Both peptides stimulated p21ras at low concentrations with a maximal response obtained at 10 ng/ml for each peptide, idicating that insulin and IGF-I activate ras by interacting with their homologous receptor. Pretreatment of neurons with lovastatin (2 micrograms/ml), an inhibitor of ras isoprenylation, completely blocked the activation of p21ras by insulin and IGF-I. Lovastatin also blocked the ability of these growth factors to support the survival and differentiation of fetal chick neurons in culture. We conclude that insulin and IGF-I activate p21ras in fetal chick forebrain neurons by increasing the amount of GTP bound to p21ras. The activation of neuronal p21ras is necessary for insulin and IGF-I to promote survival and differentiation in these neurons.

Animals↗
PubMed1993

Insulin activates p21Ras and guanine nucleotide releasing factor in cells expressing wild type and mutant insulin receptors.

Insulin stimulates the formation of p21RasGTP in Rat-1 fibroblasts overexpressing wild type (HIRc) or mutant (delta CT and Y/F2) insulin receptors. Maximal insulin effect was observed at 7 min in Y/F2 cells, at 10 min in delta CT cells, and at 15 min in HIRc cells. Mutant insulin receptors which display enhanced mitogenic signaling properties stimulated p21Ras.GTP formation to a greater extent than wild type receptors. The amount of p21Ras was not affected by insulin (Western blotting). Tyrosine kinase inhibitor, Lavendustin A (10 nM), completely prevented insulin-induced activation of p21Ras in all cell lines. Insulin did not lead to GAP phosphorylation, or a change in cellular GAP activity, but did result in marked stimulation of Ras guanine nucleotide releasing factor (GRF) activity (by 48% in HIRc, 71% in delta CT, and 120% in Y/F2 cells). These results indicated that p21Ras.GTP is an important signaling molecule in insulin's mitogenic pathway, but may not participate in metabolic signaling and that insulin's stimulatory effects on p21Ras.GTP formation are mediated through Ras GRF.

Animals↗
PubMed1993

Mechanism of impaired metabolic signaling by a truncated human insulin receptor. Decreased activation of protein phosphatase 1 by insulin.

Previous studies have shown that a human insulin receptor lacking the COOH-terminal 43-amino acid domain (HIR delta CT) displays a compromised ability to stimulate glucose transport and glycogen synthase, whereas mitogenic signaling and stimulation of the insulin receptor tyrosine kinase activity remain intact (Maegawa, H., McClain, D. A., Freidenberg, G., Olefsky, J. M., Napier, M., Lipari, T., Dull, T. J., Lee, J., and Ullrich, A. (1988) J. Biol. Chem. 263, 8912-8917). In this study, we examined the effect of insulin on protein phosphatase 1 (PP-1) activity and phosphorylation in cells expressing wild-type human insulin receptor (HIRc) and HIR delta CT cells using phosphorylase alpha as substrate in the presence of 3 nM okadaic acid. Basal PP-1 activity was significantly lower in HIR delta CT than in HIRc cells (p < 0.05). Insulin stimulated PP-1 activity in HIRc cells (25-30% increase over basal activity) in a time- and dose-dependent manner. Insulin failed to stimulate PP-1 activity in HIR delta CT cells. Western blotting with the catalytic subunit antibody and the regulatory subunit antibody revealed similar amounts of the 37-kDa band (catalytic subunit) and the 160-kDa band (presumed regulatory subunit) in HIRc and HIR delta CT cells. We conclude that the COOH-terminal domain of the insulin receptor is an important element in mediating the effect of insulin on PP-1 and suggest that activation of PP-1 may be linked to signaling insulin's metabolic actions.

Animals↗
PubMed1993

GLUT-4 phosphorylation and its intrinsic activity. Mechanism of Ca(2+)-induced inhibition of insulin-stimulated glucose transport.

In this study, we examined the influence of high levels of cytosolic calcium on phosphorylation status and function of GLUT-4 in isolated rat adipocytes. Intracellular calcium was elevated by exposing adipocytes to either extracellular ATP (1.6 mM) or thapsigargin (100 nM). Both agents increased cytosolic calcium 2-3 fold. While basal glucose uptake was unaffected, both ATP and thapsigargin reduced insulin-stimulated glucose transport by 40-70% (p < 0.05). Neither ATP nor thapsigargin affected GLUT-4 content or its translocation from the low density microsomes to the plasma membrane (PM). In contrast, GLUT-4 immunoprecipitated from the PM of adipocytes exposed to either ATP or thapsigargin was phosphorylated to a greater extent than the GLUT-4 isolated from control cells. ATP and thapsigargin also abolished insulin-stimulated dephosphorylation of GLUT-4. At the same time, GLUT-4 intrinsic activity was significantly reduced in adipocytes with high levels of cytosolic calcium (p < 0.05). Preincubation of adipocytes with cAMP antagonist, RpcAMP (10(-4) M), and calcium channel blocker, nitrendipine (30 microM), improved the ability of insulin to dephosphorylate GLUT-4 and restored insulin-stimulated GLUT-4 intrinsic activity. We conclude that elevated levels of cytosolic calcium interfere with insulin's ability to dephosphorylate GLUT-4, thus reducing its intrinsic activity.

Adenosine Triphosphate↗
PubMed1993

Inverse relationship between GLUT-4 phosphorylation and its intrinsic activity.

In this study, we examined the effect of phosphorylation on GLUT-4 function in isolated rat adipocytes. Adipocytes labeled with 32P for 2 h were incubated with parathyroid hormone (PTH) (20 ng/ml) for 60 min and then exposed to insulin (25 ng/ml) for an additional 30 min. 32P-GLUT-4 was immunoprecipitated from the plasma membrane and low density microsomal fractions, and its degree of phosphorylation was determined by autoradiography and densitometry. Results were expressed as 32P-GLUT-4 specific activity (phosphorylation/unit of protein). GLUT-4 intrinsic activity was measured using [14C]2-deoxyglucose uptake in plasma membrane vesicles. PTH significantly increased GLUT-4 phosphorylation and eliminated the insulin-stimulated dephosphorylation of GLUT-4. Western blotting revealed normal distribution of GLUT-4 before and after insulin stimulation in control and PTH-treated cells, suggesting that phosphorylation of GLUT-4 does not interfere with its recruitment to the plasma membrane. In contrast, intrinsic activity of phosphorylated GLUT-4 was significantly reduced (p < 0.01). Preincubation of adipocytes with calcium channel blocker (nitrendipine) and cyclic AMP antagonist (RpcAMP) restored GLUT-4 intrinsic activity in the PTH-treated cells. In several experiments, GLUT-4 was phosphorylated in vitro in plasma membrane vesicles isolated from normal adipocytes exposed to insulin. This in vitro phosphorylation reduced GLUT-4 intrinsic activity by approximately 35% (p < 0.01). We conclude that phosphorylation of GLUT-4 significantly impairs the ability of insulin to stimulate its intrinsic activity.

Adipose Tissue↗
PubMed1993

Cytosolic calcium and insulin resistance.

The presence of insulin resistance in many patients with hypertension has become a well-recognized phenomenon. However, the mechanism of this association remains enigmatic. We have hypothesized that abnormal cellular calcium handling, particularly elevations in cytosolic free calcium concentrations, may represent a common intracellular abnormality (a missing link) that is responsible for the frequent co-existence of insulin resistance and hypertension. We have shown recently that sustained elevations of cytosolic free calcium in insulin target cells, such as are observed in patients with obesity and non-insulin-dependent diabetes mellitus and in some patients with hypertension, may lead to the development of insulin resistance. Although the mechanisms that lead to such increases are not yet well understood, they appear to include an enhanced influx of calcium via calcium channels. We found that the presence of the calcium antagonist nitrendipine in the incubation medium prevented increases in cytosolic free calcium concentration and ameliorated the insulin resistance induced by various mechanisms. To further evaluate the existence of an association between elevated levels of cytosolic calcium and diminished cellular sensitivity to insulin in patients with essential hypertension, we studied insulin sensitivity in vivo and in vitro in isolated adipocytes from older hypertensive, nondiabetic subjects. Obese hypertensive individuals demonstrated marked hyperinsulinemia and significantly reduced submaximally stimulated adipocyte 2-deoxyglucose uptake. One month of therapy with nitrendipine (10 mg twice daily) reduced blood pressure in hypertensive subjects, reduced plasma insulin to control values in obese hypertensive individuals, and restored adipocyte 2-deoxyglucose uptake at at submaximally effective insulin concentrations to control values in both obese hypertensive subjects and those of normal weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Protein phosphatase-1 and -2a activities in cultured fetal chick neurons: differential regulation by insulin and insulin-like growth factor-I.

In this study, we examined the developmental expression and regulation by insulin and insulin-like growth factor-I (IGF-I) of protein phosphatase-1 (PP-1) and protein phosphatase-2A (PP-2A) in cultured fetal chick neurons. Protein phosphatase activities were measured using 32P-labeled phosphorylase-a or 32P-labeled S6 kinase substrate peptide. In cell extracts from day 1-5 cultures, 40-45% of spontaneous protein phosphatase activity was due to PP-1. PP-2A accounted for the remaining 55-60% of enzyme activity. Spontaneous PP-1 activity increased by 100% in day 2 cultures and remained constant thereafter. PP-2A activity increased by 48% in day 2 cultures, with minimal increases in enzyme activity in later cultures. Under the assay conditions employed, at all times in culture a significant proportion (45-50%) of PP-1 was in an inactive form that could be reactivated by trypsin. PP-2A activity was not influenced by trypsin. Insulin stimulated neuronal PP-1 activity in day 4 and 5 cultures, but had no effect in earlier cultures. The activation of PP-1 by insulin was rapid, with a maximal effect (30-40% increase over basal levels) at 5 min with 10 ng/ml insulin. Insulin did not alter total (trypsin-released) PP-1 activity, the content of PP-1 catalytic subunit, or PP-2A activity at any time in culture. In contrast to insulin, IGF-I had no effect on PP-1 activity at any time in culture, but significantly increased PP-2A activity in day 5 cultures. Maximal stimulation of PP-2A activity by IGF-I was observed at 10 min, with an EC50 of 5 ng/ml. These results indicate that chick forebrain neurons contain both PP-1 and PP-2A activities and that neuronal PP-1 and PP-2A activities are differentially regulated by insulin and IGF-I. We conclude that although insulin and IGF-I share many steps in signal transduction, these growth factors have distinct actions on neuronal phosphatase activity that may impact on differences in their neurotropic actions.

Animals↗
PubMed1992

Calcium-induced inhibition of phosphoserine phosphatase in insulin target cells is mediated by the phosphorylation and activation of inhibitor 1.

In this study, we examined the mechanism of inhibition of phosphoserine phosphatase (PSPase) activity by elevated [Ca2+]i in insulin target cells. In in vitro studies, isolated rat adipocytes were incubated with either 40 mM K+ or parathyroid hormone (PTH) (20 ng/ml) for 1 h. In in vivo studies, rats were injected with PTH (three hourly injections of 40 micrograms intraperitoneally) prior to isolation of either adipocytes or skeletal muscle. Under these conditions, intracellular [Ca2+]i changed from 100 +/- 8.7 to 263 +/- 10.5 nM. There was a concomitant 30% decrease in adipocyte PSPase activity and a 35% decrease in skeletal muscle PSPase activity, assayed using 32P-labeled phosphorylase "a" as a substrate. The inhibition of PSPase was accompanied by a 60% increase in adipocytes (p less than 0.05) and a 118% increase (p less than 0.01) in skeletal muscle inhibitor 1 (I1) activities, respectively. Since I1 is active only in the phosphorylated state, we studied the effect of [Ca2+]i on I1 phosphorylation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of heat treated extracts immunoprecipitated with I1 antibody revealed significant increase in 32P incorporation (45-60%, p less than 0.05) into I1 protein in cells with elevated [Ca2+]i. Nitrendipine, a calcium channel blocker, completely prevented increases in I1 phosphorylation and activity in cells exposed to K+ but was only partially effective in the PTH-treated cells. In contrast, a cyclic AMP antagonist, RpcAMP, prevented both the K(+)-and the PTH-induced increases in I1 phosphorylation and activity, even though it failed to block the elevations in [Ca2+]i in these cells. We conclude that [Ca2+]i-induced and cAMP-mediated phosphorylation and activation of I1 results in inhibition of PSPase activity in insulin target cells. The inhibition of PSPases may cause inappropriate serine dephosphorylation of substrates of insulin action resulting in insulin resistance.

Adipose Tissue↗
PubMed1992

Na+/K(+)-ATPase activity and its alpha II subunit gene expression in rat skeletal muscle: influence of diabetes, fasting, and refeeding.

We have examined the effects of diabetes, fasting, and refeeding on Na+/K(+)-adenosine triphosphatase (ATPase) activity and its catalytic alpha II subunit gene expression in skeletal muscle. Two hypoinsulinemic states, streptozotocin-induced diabetes and 48-hour fasting caused a significant decrease (P less than .05) in skeletal muscle Na+/K(+)-ATPase activity and a marked increase (P less than .01) in the levels of alpha II subunit mRNA. A decrease in enzyme activity was observed on the 2nd and the 14th day of diabetes, whereas an increase in alpha II mRNA levels was found only on the 14th day. The levels of alpha I mRNA were not affected, while the levels of mRNA of the structural beta subunit were decreased on the 14th day of diabetes. Correction of hyperglycemia with insulin restored enzyme activity and alpha II isoform mRNA levels toward normal in diabetic animals. Refeeding for 48 or 72 hours restored these parameters to normal in skeletal muscle of previously fasting rats. These observations suggest that a decrease in muscle Na+/K(+)-ATPase activity may lead to a compensatory increase in its alpha II subunit gene expression. The levels of insulin and not of glycemia appear to be critical in modulating Na+/K(+)-ATPase activity and gene expression.

Animals↗
PubMed1992

Cytosolic calcium and insulin resistance in elderly patients with essential hypertension.

We evaluated insulin sensitivity in normotensive (blood pressure, BP, less than 135/85 mm Hg) and hypertensive (BP greater than 160/90 mm Hg) elderly subjects over 65 years old who were stratified as normal weight (body mass index, BMI, less than 27) and obese (BMI greater than 27). Obese hypertensive individuals demonstrated marked hyperinsulinemia (P less than .01) and significantly reduced (P less than .05) submaximally stimulated adipocyte 2-deoxyglucose (2-DOG) uptake (abdominal wall fat biopsy). Normal weight hypertensive subjects also demonstrated higher levels of insulinemia and lower insulin-stimulated 2-DOG uptake than nonobese controls. Adipocyte [Ca2+]i levels were elevated in all elderly subjects compared to young individuals (P less than .01). Basal and maximally stimulated 2-DOG uptake were similar in all groups. One month of therapy with a calcium channel blocker, 10 mg nitrendipine twice daily, reduced blood pressure in the hypertensive subjects, reduced plasma insulin to control values during an oral glucose tolerance test in obese hypertensive individuals (P less than .01), and restored adipocyte 2-DOG uptake at submaximally effective insulin concentration to control values in normal weight and obese hypertensive subjects. In summary, older hypertensive, and particularly older obese hypertensive, patients manifest significant insulin resistance accompanied by elevated levels of [Ca2+]i in their adipocytes.

Adipose Tissue↗
PubMed1992

Role of cAMP in mediating effects of fasting on dephosphorylation of insulin receptor.

We studied the effect of fasting on phosphotyrosine phosphatase (PTPase) activities in particulate (PF) and cytosolic (CF) fractions of rat adipocytes and liver. PTPase activity was assessed using [32P]tyrosine insulin receptor (IR). In adipocytes, 48 h fasting significantly inhibited PTPase activity. Dephosphorylation of IR by PF and CF PTPases was reduced by 80 and 65%, respectively. Similar reductions of lesser magnitude were observed in fasted rat livers. The effect of fasting was completely reversed by either refeeding or by incubating "fasted" adipocytes for 2 h in tissue culture medium containing 5 mM glucose. Neither 20 mM glucose nor the presence of insulin influenced phosphatase activity. Because fasting is accompanied by elevated protein kinase C (PKC) and adenosine 3',5'-cyclic monophosphate (cAMP) levels, we examined their influence on adipocyte PTPases. Neither activation (1 microM 12-O-tetradecanoylphorbol-13-acetate) nor inhibition (20 microM sphingosine) of PKC affected PTPase activity. In contrast, cAMP (2 mM) significantly inhibited PTPase activity (80% inhibition at 2 h), and its effect was prevented by a cAMP antagonist RpcAMP. Fasting- and cAMP-induced inhibition of PTPase activity was restored by incubating PF with trypsin (4 micrograms/ml for 5 min), which separated the putative inhibitors from the phosphatases. We conclude that fasting-induced inhibition of PTPases is mediated by elevated cAMP levels, most likely by activating phosphatase inhibitors.

Adipose Tissue↗
PubMed1992

Effect of streptozotocin-induced diabetes on GLUT-4 phosphorylation in rat adipocytes.

We have examined the regulation of GLUT-4 phosphorylation in adipocytes isolated from diabetic rats. Despite progressive (40-70%) reductions in GLUT-4 protein contents on the 2nd, 7th, and 14th day of diabetes, the phosphorylation of GLUT-4 was increased two- to fourfold. These alterations were accompanied by concomitant reductions (40-66%) in the insulin-stimulated 2-deoxyglucose transport. Insulin treatment of diabetic animals for 5 d restored glucose transport activity, GLUT-4 protein, and GLUT-4 phosphorylation to control levels whereas vanadate and phlorizin were ineffective. In control adipocytes, insulin promoted GLUT-4 translocation from the low density microsomal (LDM) pool to the plasma membranes (PM) and decreased the state of GLUT-4 phosphorylation. In adipocytes isolated from the diabetic rats, insulin failed to stimulate GLUT-4 translocation and to decrease GLUT-4 phosphorylation. To explore the mechanism of the diabetes-induced increases in the GLUT-4 phosphorylation, we investigated phosphoserine phosphatase (PSPase) activities using 32P-labeled GLUT-4 and phosphorylase "a" as substrates. Diabetes resulted in 50-60% increase in the particulate PSPase activity and concomitant reductions in cytosolic PSPase activities. Although reduced cytosolic PSPase activity correlated with an inadequate dephosphorylation of LDM GLUT-4, the existence of highly phosphorylated PM GLUT-4 in the presence of increased particulate PSPase activity required additional explanation. To address this problem, we used PM GLUT-4 from diabetic rats as a substrate of particulate PSPase. Highly active diabetic particulate PSPase, which dephosphorylated control GLUT-4 and phosphorylase a, failed to dephosphorylate PM GLUT-4 from diabetic rats. These data suggest that PM GLUT-4 from diabetic rats is unable to interact with PSPase or that its phosphorylation sites are not accessible to PSPase action. In summary, an induction of diabetes with streptozotocin resulted in significant increases in GLUT-4 phosphorylation. In contrast to normal cells, insulin failed to promote GLUT-4 recruitment to the plasma membranes and its dephosphorylation in diabetic adipocytes. At the same time, diabetes appears to induce redistribution of PSPases, resulting in lower cytosolic activity and higher particulate activity. It also appears that the existence of highly phosphorylated GLUT-4 in the plasma membranes of diabetic adipocytes resulted from its inability to interact with particulate PSPases.

Adipose Tissue↗
PubMed1991

Gene expression of type I phospholipase A2 in pancreatic beta cells. Regulation of mRNA levels by starvation or glucose excess.

Messenger RNA from intact rat pancreatic islets, or from transformed hamster beta (HIT) cells, hybridized with the cDNA probe for type I (but not type II) phospholipase A2. The levels of phospholipase A2 mRNA increased in islets from fasted rats; they decreased in islets cultured in a high glucose concentration (control values at 5.5 mM glucose = 150 +/- 6% of those at 22 mM) which impaired subsequent insulin secretion (reduction in second-phase release = 70 +/- 11%). These studies uniquely demonstrate that type I phospholipase A2 is expressed specifically in beta cells and that nutrient availability modulates transcript levels, an effect which could that nutrient availability modulates transcript levels, an effect which could contribute to the detrimental influence of prolonged hyperglycemia on islet function.

Animals↗
PubMed1991

High levels of cytosolic free calcium inhibit dephosphorylation of insulin receptor and glycogen synthase.

Treatment of adipocytes with depolarizing concentrations of K+ (40 mM) for 60 min increased [Ca2+]i from 158 +/- 28 nM to 328 +/- 38 nM. This significantly reduced (up to 80% inhibition) dephosphorylation of insulin receptor (IR), EGF receptor (EGF-R) and glycogen synthase (GS). The calcium channel blocker, nitrendipine (30 microM), or Ca2+ free medium completely prevented K(+)-induced inhibition of phosphoprotein phosphatase (PPTase). This effect of high [Ca2+]i was completely reversible when the cells were returned into the non-depolarizing medium. Trypsin treatment (4 micrograms/ml) of the membrane fraction containing inhibited PPTase activity, restored dephosphorylation activity to normal suggesting that elevated [Ca2+]i may inhibit PPTase by promoting its association with the inhibitors. These observations indicate that dephosphorylation of IR and GS can be regulated by [Ca2+]i.

Adipose Tissue↗
PubMed1991

Regulation of GLUT-4 phosphorylation by intracellular calcium in adipocytes.

Sustained elevations in cytosolic calcium concentrations ([Ca2+]i) have been shown to render insulin target cells resistant to insulin action. In this study we examined the mechanisms of the detrimental effect of high levels of [Ca2+]i on insulin-induced 2-deoxyglucose (2-DOG) uptake. To elevate [Ca2+]i, we incubated rat adipocytes with either 40 mM potassium (K+) or 20 ng/ml PTH for 1 h for in vitro experiments and injected rats with PTH (injections of 50 micrograms, ip, every hour for 3 h) for in vivo studies. Adipocytes with elevated [Ca2+]i demonstrated a 30% decrease in insulin-stimulated 2-DOG uptake. A calcium channel blocker (nitrendipine) and a cAMP antagonist (RpcAMP) each partially restored insulin-stimulated glucose transport, but together they completely restored 2-DOG uptake. Concomitantly, we found a significant increase in phosphorylation of GLUT-4 in adipocytes with elevated [Ca2+]i. This change in GLUT-4 phosphorylation was also attenuated by nitrendipine and RpcAMP. These observations confirm that elevated [Ca2+]i diminishes insulin-stimulated glucose transport and suggest that increased phosphorylation of GLUT-4 in adipocytes with high [Ca2+]i may alter its intrinsic activity.

Adipose Tissue↗
PubMed1991

Effect of diabetes on cytosolic free Ca2+ and Na(+)-K(+)-ATPase in rat aorta.

We examined Na(+)-K(+)-ATPase activity and the levels of alpha I-, alpha II-, and beta-subunit mRNA and protein in aortic cells of diabetic rats. Diabetes was induced by streptozocin. Na(+)-K(+)-ATPase activity was significantly reduced on the 2nd day of diabetes (9.4 +/- 1.3 vs. 17.5 +/- 2.1 mumol NADH.mg-1 protein.h-1, P less than 0.05) and remained depressed on days 7 and 14. The levels of 5.3-kilobase (kb) mRNA band of the catalytic alpha II-subunit of Na(+)-K(+)-ATPase were also decreased on the 2nd day of diabetes, whereas the second band, 3.4 kb, was not affected. Both bands were significantly decreased on days 7 and 14. This was followed by a reduction in the levels of alpha II-protein (day 14). The levels of alpha I- and beta-subunit mRNA and alpha I- protein were not affected by diabetes. A decrease in Na(+)-K(+)-ATPase activity was accompanied by a significant (P less than 0.001) increase in the cytosolic free Ca2+ concentrations [( Ca2+]i) in diabetic aortic cells (221 +/- 18 nM on the 7th day and 242 +/- 17 nM on the 14th day vs. 153 +/- 7 nM in controls). These findings are consistent with the hypothesis that decreased Na(+)-K(+)-ATPase activity and gene expression in vascular smooth muscle cells with accompanied rises in [Ca2+]i may be an important pathogenetic factor in the development of hypertension and atherosclerosis in diabetes.

Animals↗
PubMed1991

Differential effects of diabetes on adipocyte and liver phosphotyrosine and phosphoserine phosphatase activities.

We examined the activities of particulate and cytosolic phosphotyrosine phosphatase (PTPase) and phosphoserine phosphatase (PSPase) in adipocytes and livers of diabetic rats. PTPase activity was assessed with [32P]tyrosine-phosphorylated insulin receptor (IR), whereas PSPase activity was assayed with [32P]serine-phosphorylated glycogen synthase. Diabetes increased adipocyte particulate PTPase activity and enhanced IR dephosphorylation by 75% on the 2nd, 93% on the 14th, and 108% on the 30th day. In contrast, cytosolic PTPase activity decreased by 78% on the 14th and 45% on the 30th day (no change on the 2nd day). Similar changes were observed with PSPase (increased activity in particulate and decreased in cytosolic). Insulin therapy for 14 or 30 days restored PTPase and PSPase activities in both fractions. Vanadate, despite rapid normalization of glycemia, restored these activities only after 30 days of therapy. Diabetes-related changes in liver PTPase activity were observed on the 14th day only. At this time, it was increased in both particulate and cytosolic fractions. There was spontaneous normalization of the liver PTPase activity at 30 days of diabetes. In contrast, liver cytosolic PSPase activity was significantly inhibited and not normalized by the 30th day of disease without therapy. In summary, diabetes appears to induce tissue-specific changes in PTPase and PSPase activities resulting in significant alterations in dephosphorylation of IR and glycogen synthase. Moreover, there appears to be a differential regulation of PTPase and PSPase activities in diabetes, particularly in the liver.

Adipose Tissue↗