cytochalasin-b and Body-Weight

The influence of passive tension on contractions to phorbol 12,13-dibutyrate (1 microM PBDu) on the thoracic aorta of Wistar and SHR rats, aged 8-12 weeks, and the functional importance of both the actin and the tubulin components of the cytoskeleton, were studied. Contractile responses to PBDu (1 microM) were obtained in aorta rings, at two levels of passive tension: 3 and 0.5g. These responses were expressed as percentage of the maximal response to noradrenaline obtained in the beginning of the experiment at a tension of 2g. Responses to PBDu were significantly larger (P<0.05) at 3g than at 0.5g in both kinds of rats: 226.5+/-34.4%, n=6, versus 143.0+/-28.5%, n=6, respectively, for SHR; 153.0+/-12.9%, n=8, versus 109.0+/-7.3%, n=7, respectively, for Wistar rats. Responses to PBDu were markedly decreased by cytochalasin B (50 microM) (to 61.3+/-14.3%, n=6, at 3g, and 29.6+/-17.8%, n=5, at 0.5g in SHR; to 18.5+/-0.9%, n=6, at 3g, and 6.4+/-1.8%, n=5, at 0.5g in Wistar rats). Colchicine (100 microM) failed to produce a decrease in responses to PBDu in both strains of rats. It is concluded that responses to phorbol ester action depend on passive tension. This difference may depend on filament interaction. Contractions to PBDu in the rat aorta may be highly dependent on actin polymerization.

Topics: Actins; Animals; Aorta, Thoracic; Body Weight; Colchicine; Cytochalasin B; Cytoskeleton; Hypertension; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth, Vascular; Phorbol 12,13-Dibutyrate; Protein Kinase C; Rats; Rats, Inbred SHR; Rats, Wistar; Tubulin Modulators

D-fructose transport was characterized in renal brush-border membrane vesicles (BBMVs) from both spontaneously hypertensive rats (SHR) and normotensive genetic control Wistar-Kyoto (WKY) rats. Kinetic studies indicated that the maximal rate (Vmax) of D-fructose transport was significantly lower in SHR compared with WKY rats. No differences were observed in the Michaelis constant (Km) or the diffusion constant (Kd) between the two groups of animals. D-fructose inhibited its own transport, whereas the presence of D-glucose, D-galactose, phlorizin, and cytochalasin B did not inhibit the transport of D-fructose in either animal group. To explain the reduction in D-fructose transport in SHR, the density of the D-fructose transporter, GLUT5, was analyzed by Western blot. GLUT5 levels were lower in SHR, a reduction similar to that of the Vmax. Thus, there appears to be a high-affinity, low-capacity, GLUT5-type fructose carrier in the apical membranes of rat kidney cortex, and the decrease in the Vmax of D-fructose transport in renal BBMVs from hypertensive rats correlates well with a reduction in the expression of GLUT5 protein.

Topics: Animals; Biological Transport; Blood Pressure; Body Weight; Cytochalasin B; Fructose; Galactose; Glucose; Glucose Transporter Type 5; Hypertension; Immunoblotting; Kidney; Male; Microvilli; Monosaccharide Transport Proteins; Phlorhizin; Potassium; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Sodium; Transport Vesicles

1. The present study aimed at comparing the influence of passive tension on the effect exerted by noradrenaline on the thoracic aorta of 6-month-old Wistar and spontaneously hypertensive rats (SHR). 2. Concentration-response curves to noradrenaline were obtained in aorta rings, at two levels of passive tension: 3 and 0.5 g. 3. The maximal responses (in percentage of the maximal response to noradrenaline obtained in the beginning of the experiment at a tension of 2 g) were significantly larger (P < 0.05) at 3 g than at 0.5 g in both kinds of rats: 171 versus 69%, respectively, for SHR; 139 versus 76%, respectively, for Wistar rats. 4. When expressed as mg of active tension per mg of tissue, the maximal contraction at both 3 and 0.5 g was smaller in SHR than in Wistar rats (at 3 g: 64.6 +/- 6.7, n = 6 versus 122.3 +/- 19.1, n = 8, respectively, P < 0.05; at 0.5 g: 24.0 +/- 1.0, n = 6 versus 49.0 +/- 5.9, n = 8, respectively, P < 0.05). 5. Maximal responses to noradrenaline were markedly decreased by cytochalasin B (50 microM) (to 15.2 +/- 6.0%, n = 6, at 3 g and 2.8 +/- 1.9%, n = 6, at 0.5 g in SHR; to 11.8 +/- 2.3%, n = 4, at 3 g and 4.3 +/- 1.3%, n = 4, at 0.5 g in Wistar rats). Cytochalasin B at a lower concentration (4 microM) produced a less marked decrease in responses to noradrenaline in both strains of rats. The presence of cardiovascular structural changes in SHR was confirmed by the fact that the heart weight (mg):body weight (g) was higher in SHR (3.37 +/- 0.06, n = 10) than in Wistar rats (2.40 +/- 0.12, n = 11) (P < 0.05). 6. It is concluded that in 6-month-old SHR the contractile capacity of the aortic tissue is reduced. However, the differential sensitivity of aortic smooth muscle at the two different levels of tension remains present. This difference may depend on filament interaction. Contractions to noradrenaline in the rat aorta are highly dependent on actin polymerization.

Topics: Animals; Aorta, Thoracic; Body Weight; Cytochalasin B; Hypertension; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth, Vascular; Norepinephrine; Organ Size; Rats; Rats, Inbred SHR; Rats, Wistar; Vasoconstrictor Agents

The pharmacological action of mazindol (5-hydroxy-5-p-chlorophenyl-2,3-dihydro-5-imidazo[2,1-a]isoindo l) was examined by studying its effect on glucose uptake by rat tissues using radiolabelled 2-deoxy-D-glucose. The following results were obtained. (1) The rate constant (Ki) of net tissue 2-deoxy-D-glucose uptake increased in the cerebral cortex (4.7-fold, P < 0.05), the hypothalamus (4.6-fold, P < 0.05), heart (4.0 fold, P < 0.05) and skeletal muscles (gastrocnemius, 5.7-fold, P < 0.01; soleus, 4.7-fold, P < 0.05), but not in epididymal adipose tissue in vivo 90 min after intragastric administration of mazindol (20 mg/kg). (2) This increase in Ki values of net tissue 2-deoxy-D-glucose uptake was not observed after addition of mazindol to the diet (40 mg/100 g of diet) for 4 days. (3) Mazindol (16.7 ng/ml to 16.7 micrograms/ml) stimulated 2-deoxy-D-glucose transport into sarcolemmal vesicles of the gastrocnemius muscle in vitro (1.6-1.8-fold, P < 0.05) and this stimulation was blocked by cytochalasin B (10 microM). These findings suggest that mazindol stimulates glucose transport into skeletal muscles by acting on glucose transporters in the sarcolemmal membrane, and suggest that mazindol may stimulate glucose transport into the brain and heart by a similar mechanism.

Topics: Animals; Body Weight; Brain Chemistry; Cytochalasin B; Deoxyglucose; Eating; Glucose; In Vitro Techniques; Insulin; Male; Mazindol; Muscle, Skeletal; Rats; Rats, Wistar; Sarcolemma; Stimulation, Chemical

High-fat diet (HFD) induces skeletal muscle insulin resistance. To investigate associated changes in the plasma membrane glucose transporter, male Sprague-Dawley rats were fed either chow [high-carbohydrate diet (HCD)] or HFD for 3 wk. Plasma membrane vesicles were prepared from hindlimb muscle of control, insulin-stimulated (Ins), and acutely exercised (Ex) rats. Maximal vesicle glucose transport activity (Vmax) increased threefold with Ins and Ex treatment compared with controls in HCD rats; in HFD rats, increases were less than twofold. Transporter numbers (measured by cytochalasin B binding, CB) approximately doubled with Ins and Ex in both diet groups. Intrinsic activity (carrier turnover, Vmax/CB) increased significantly with stimulation in HCD but not HFD rats. Therefore, vesicles from HFD rats showed resistance to both exercise and insulin stimulation of muscle glucose transport. Transporter number increased normally, but intrinsic activity in HFD rats did not respond. Two conclusions are discussed: 1) translocation and activation are distinct, separable steps in transporter stimulation and 2) HFD produces effects that resemble the insulin resistance of starvation.

Topics: 4-Nitrophenylphosphatase; Animals; Blood; Body Weight; Cell Membrane; Cytochalasin B; Dietary Carbohydrates; Dietary Fats; Glucose Transporter Type 4; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Physical Exertion; Potassium; Rats; Rats, Sprague-Dawley

Endurance exercise training can result in increased rates of insulin-stimulated glucose uptake in skeletal muscle; however, this effect may be lost rapidly once training ceases. To examine a mechanism for these changes, the skeletal-muscle glucose transport system of female rats exercise-trained in wheelcages for 6 wk were studied against a group of untrained female rats. The trained rats were studied immediately following and 2 and 5 days after removal from wheelcages; both trained and untrained rats were studied 30 min after insulin (90 nmol/rat, intraperitoneal) or saline injection. The total number of skeletal-muscle plasma-membrane glucose transporters (R0), total muscle-homogenate and plasma-membrane GLUT4 protein, and rates of plasma-membrane vesicle D-facilitated glucose transport were higher in the exercise-trained rats immediately after exercise training and did not decrease significantly during the 5 days after cessation of training. On the other hand, exercise training did not alter microsomal-membrane total glucose-transporter number or GLUT4 protein, nor did training alter GLUT1 protein in total muscle homogenates nor either membrane fraction. The carrier-turnover number, an estimate of average functional activity of glucose transporters in the plasma membrane, was elevated slightly, but not significantly, in the trained muscle. In both the trained and untrained muscle, insulin administration resulted in translocation of glucose transporters from the microsomal-membrane fraction to the plasma membrane and an increase in the carrier-turnover number.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 4-Nitrophenylphosphatase; Animals; Blood Glucose; Blotting, Western; Body Weight; Cell Membrane; Citrate (si)-Synthase; Cytochalasin B; Eating; Female; Glucose; Glucose Transporter Type 1; Glucose Transporter Type 4; Glycogen; Insulin; Isomerism; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Physical Conditioning, Animal; Rats; Rats, Inbred Strains; Subcellular Fractions

Skeletal muscle contractile activity results in increased rates of glucose transport that are associated with an increase in the number and activity of plasma membrane glucose transporters. In the current study it was determined whether exercise causes a translocation of glucose transporters from an intracellular pool to the plasma membrane and whether exercise and insulin stimulate the same glucose transporter protein. Plasma membrane glucose transporter number, measured by cytochalasin B binding, increased from 10.1 +/- 0.73 to 15.0 +/- 1.4 pmol/mg protein (P less than 0.01) in muscle of exercised rats, whereas microsomal membrane transporters decreased significantly from 6.0 +/- 0.7 to 4.2 +/- 0.4 pmol/mg protein (P less than 0.05). Western blot analysis using the monoclonal antibody mAb 1F8 (specific for GLUT-4) demonstrated a 45% increase in plasma membrane GLUT-4 from exercised skeletal muscle compared with controls, whereas microsomal membranes from the exercised muscle had a concomitant 25% decrease in GLUT-4 protein. These data suggest that exercise recruits transporters to the plasma membrane from an intracellular microsomal pool, similar to the translocation of transporters that occurs with insulin stimulation. Furthermore, both exercise and insulin stimulate the translocation of GLUT-4 in skeletal muscle, while GLUT-1 is not altered.

Topics: 4-Nitrophenylphosphatase; Adenosine Triphosphatases; Animals; Biological Transport; Blotting, Western; Body Weight; Cell Membrane; Cytochalasin B; Insulin; Male; Monosaccharide Transport Proteins; Muscles; Organ Size; Physical Exertion; Potassium; Rats; Rats, Inbred Strains

The purpose of this study was to simultaneously isolate skeletal muscle plasma and microsomal membranes from the hind limbs of male Sprague-Dawley rats perfused either in the absence or presence of 20 milliunits/ml insulin and to determine the effect of insulin on the number and distribution of glucose transporters in these membrane fractions. Insulin increased hind limb glucose uptake greater than 3-fold (2.4 +/- 0.7 versus 9.2 +/- 1.0 mumol/g x h, p less than 0.001). Plasma membrane glucose transporter number, measured by cytochalasin B binding, increased 2-fold (9.1 +/- 1.0 to 20.4 +/- 3.1 pmol/mg protein, p less than 0.005) in insulin-stimulated muscle while microsomal membrane transporters decreased significantly (14.8 +/- 1.6 to 9.8 +/- 1.4 pmol/mg protein, p less than 0.05). No change in the dissociation constant (Kd approximately 120 nm) was observed. K+-stimulated-p-nitrophenol phosphatase, 5'-nucleotidase, and galactosyltransferase specific activity, enrichment, and recovery in the plasma and microsomal membrane fractions were not altered by insulin treatment. Western blot analysis using the monoclonal antibody mAb 1F8 (specific for the insulin-regulatable glucose transporter) demonstrated increased glucose transporter densities in plasma membranes from insulin-treated hind limb skeletal muscle compared with untreated tissues, while microsomal membranes from the insulin-treated hind limb skeletal muscle had a concomitant decrease in transporter density. We conclude that the increase in plasma membrane glucose transporters explains, at least in part, the increase in glucose uptake associated with insulin stimulation of hind limb skeletal muscle. Our data further suggest that these recruited transporters originate from an intracellular microsomal pool, consistent with the translocation hypothesis.

Topics: 5'-Nucleotidase; Adipose Tissue; Animals; Blotting, Western; Body Weight; Cell Membrane; Cytochalasin B; Electrophoresis, Polyacrylamide Gel; Galactosyltransferases; Glucose; Insulin; Male; Microsomes; Monosaccharide Transport Proteins; Muscles; Organ Size; Rats; Rats, Inbred Strains

To determine whether increased glucose transport following exercise is associated with an increased number of glucose transporters in muscle plasma membranes, the D-glucose inhibitable cytochalasin B binding technique was used to measure glucose transporters in red gastrocnemius muscle from exercised (1 h treadmill) or sedentary rats. Immediately following exercise there was a 2-fold increase in cytochalasin B binding sites, measured in purified plasma membranes enriched 30-fold in 5'-nucleotidase activity. This increase in glucose transporters in the plasma membrane may explain in part, the increase in glucose transport rate which persists in skeletal muscle following exercise. Where these transporters originate, remains to be elucidated.

Topics: 5'-Nucleotidase; Animals; Body Weight; Cell Membrane; Cytochalasin B; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Nucleotidases; Organ Size; Physical Exertion; Rats; Rats, Inbred Strains

The drug did not affect 6-hourly and daily eruption rates of the unimpeded mandibular incisor of the rat. It is suggested that the tooth eruption is not inhibited by the disruption of microfilaments because the disruption was not associated with the motility of the cells and/or that the motility of the cells is not associated with the motive force of tooth eruption. Further studies may be necessary to confirm that the effects of cytochalasin B are on both microfilaments and motility of the periodontal fibroblasts.

Topics: Animals; Body Weight; Cytochalasin B; Incisor; Male; Rats; Rats, Inbred Strains; Tooth Eruption

In order to characterize pancreatic beta cell function in Geneva bred spiny mice (acomys cahirinus), the dynamics of immunoreactive insulin release were examined during perifusion of pancreatic islets isolated from normoglycemic acomys. The initial insulin response of acomys was slow: no clear-cut early (1 to 10 min) peak of insulin release was observed when glucose in the perifusion medium was abruptly raised from 2.8 mM to concentrations as high as 56 mM. This was true for islets of either young, or older more obese acomys. However, after 20 to 30 min of perifusion at the high glucose concentrations, the rate of insulin release from acomysislets became similar to that from islets of rats or mice. By contrast, glucose-induced insulin release responses observed with islets of Wistar-derived rats, Swiss albino mice, and inbred C57BL/6J lean or obese (ob/ob) mice, were clearly biphasic. Tolbutamide 1.5 mM, arginine 16 mM, and theophylline 10 mM were ineffective in stimulating insulin release from acomys islets in the presence of a substimulatory glucose concentration (2.8 mM), whereas these agents were effective in rat islets at the same substimulatory concentration of glucose. On the other hand, when these agents, as well as cyclic AMP 10 mM or cytochalasin B 10 mug/ml were applied in the presence of a stimulating concentration of glucose (16.8 mM), the glucose-stimulated insulin release from acomys islets was increased to the same or to a greater extent than from rat islets. It is suggested that the failure of all the agents tested to stimulate an early rapid phase of insulin release from acomys islets may be secondary to the observed initial insensitivity to glucose, which insensitivity may in turn reflect a selective impairment in the recognition of glucose as an insulinogenic signal in this species.

Topics: Age Factors; Animals; Arginine; Body Weight; Cyclic AMP; Cytochalasin B; Glucose; In Vitro Techniques; Insulin; Insulin Secretion; Islets of Langerhans; Mice; Mice, Inbred C57BL; Mice, Obese; Perfusion; Rats; Species Specificity; Theophylline; Tolbutamide