Antonio Ari Gonçalves

Cooling dissociates glucose-induced insulin release from electrical activity and cation fluxes in rodent pancreatic islets

Insulin release and beta‐cell membrane potentials in response to glucose at 37 and 27 degrees C have been measured simultaneously in single, micro‐dissected, perifused islets of Langerhans from normal mice. Insulin release and 45Ca outflow in response to glucose at 37 and 27 degrees C have been measured simultaneously from perfused islets isolated by collagenase digestion from normal rats. The effect of cooling on beta‐cell membrane potassium permeability was assessed by changes in measured membrane potential and input resistance (in the mouse) and by changes in 86Rb outflow (in the rat). Resting and active beta‐cell membrane parameters (i.e. membrane potential, spike frequency, input resistance, 45Ca outflow and 86Rb outflow), in both mouse and rat islets, were affected only slightly by cooling to 27 degrees C, with temperature coefficients of 2 or lower. At 27 degrees C glucose‐stimulated insulin release was inhibited completely in mouse islets and almost completely in rat islets. The temperature coefficients in both preparations were greater than 5. It is concluded that beta‐cell electrical activity and changes in membrane permeability induced by glucose are not consequences of insulin release.

Amino acid sequence of TsTX-V, an α-toxin from Tityus serrulatus scorpion venom, and its effect on K+ permeability of β-cells from isolated rat islets of Langerhans

Highly purified Tityustoxin V (TsTX-V), an a-toxin isolated from the venom of the Brazilian scorpion Tityus serrulatus, was obtained by ion exchange chromatography on carboxymethylcellulose-52. It was shown to be homogeneous by reverse phase high performance liquid chromatography, N-terminal sequencing (first 39 residues) of the reduced and alkylated protein and by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate and tricine. Following enzymatic digestion, the complete amino acid sequence (64 residues) was determined. The sequence showed higher homology with the toxins from the venoms of the North African than with those of the North and South American scorpions. Using the rate of 86Rb+ release from depolarized rat pancreatic /gb-cells as a measure of K+ permeability changes, TsTX-V (5.6 μg/ml) was found to increase by 2.0–2.4-fold the rate of marker outflow in the presence of 8.3 mM glucose. This effect was persistent and slowly reversible, showing similarity to that induced by 100 μM veratridine, an agent that increases the open period of Na+ channels, delaying their inactivation. It is suggested that, by extending the depolarized period, TsTX-V indirectly affects β-cell voltage-dependent K+ channels, thus increasing K+ permeability.

Os efeitos da metformina sobre a dispersão do intervalo QT e QTc de ratos diabéticos

BACKGROUND Several drugs can cause prolonged QT interval, as well as prolonged QT dispersion (QTd) in electrocardiographic (EKG) recordings. QTd may be a potentially sensitive marker of increased risk of cardiac arrhythmias and sudden cardiac death. Metformin is an effective antihyperglycemic agent used in the treatment of diabetes. However, studies have correlated dose-dependent effects of metformin on glycemia and cardiovascular risk markers. OBJECTIVE To evaluate the dose-response effects of metformin on QT and QTd of diabetic rats. METHODS Male Wistar rats were distributed in five groups: non-treated control (C), non-treated diabetics (D), diabetics treated with metmorfin at the doses of 3.5, 30 and 74 microg/kg/bw (DM 3.5, DM 30 and DM 74). Diabetes was induced by an alloxan injection (40 mg/kg, IV). EKG was recorded (days 1, 15 and 30) using four electrodes inserted into the subcutaneous layer of the paws. Both RR and QT intervals were measured, and then corrected QT and QT dispersion values were calculated. RESULTS The DM 3.5 and DM 30 groups showed a significant reduction of glycemia (p< 0.05) when compared with the high dose (DM 74). Rats of the DM 74 group presented prolonged QTc, QTd and QTcd intervals, whereas rats of the DM 3.5 and DM 30 groups presented less prolonged intervals. CONCLUSION Metformin at high doses provided greater dispersion of the QT interval probably because of the increased ventricular repolarization inhomogeneity, whereas at low doses decreased QT intervals were observed in diabetic rats.BACKGROUND: Several drugs can cause prolonged QT interval, as well as prolonged QT dispersion (QTd) in electrocardiographic (EKG) recordings. QTd may be a potentially sensitive marker of increased risk of cardiac arrhythmias and sudden cardiac death. Metformin is an effective antihyperglycemic agent used in the treatment of diabetes. However, studies have correlated dose-dependent effects of metformin on glycemia and cardiovascular risk markers. OBJECTIVE: To evaluate the dose-response effects of metformin on QT and QTd of diabetic rats. METHODS: Male Wistar rats were distributed in five groups: non-treated control (C), non-treated diabetics (D), diabetics treated with metmorfin at the doses of 3.5, 30 and 74 µg/kg/bw (DM 3.5, DM 30 and DM 74). Diabetes was induced by an alloxan injection (40 mg/kg, IV). EKG was recorded (days 1, 15 and 30) using four electrodes inserted into the subcutaneous layer of the paws. Both RR and QT intervals were measured, and then corrected QT and QT dispersion values were calculated. RESULTS: The DM 3.5 and DM 30 groups showed a significant reduction of glycemia (p< 0.05) when compared with the high dose (DM 74). Rats of the DM 74 group presented prolonged QTc, QTd and QTcd intervals, whereas rats of the DM 3.5 and DM 30 groups presented less prolonged intervals. CONCLUSION: Metformin at high doses provided greater dispersion of the QT interval probably because of the increased ventricular repolarization inhomogeneity, whereas at low doses decreased QT intervals were observed in diabetic rats.

Participation of Na+ channels in the potentiation by Tityus serrulatus α-toxin TsTx-V of glucose-induced electrical activity and insulin secretion in rodent islet β-cells

The effects of TsTx-V, an α-toxin isolated from Tityus serrulatus venom, on electrical activity and insulin secretion by rodent pancreatic islet cells were studied. TsTx-V (5.6 μg/ml) depolarized mouse pancreatic β-cells, diminished the membrane input resistance and increased the duration of the active phase of glucose-induced electrical activity. Similar results were observed with the Na+ channel agonist veratridine (110 μM). Both agents potentiated glucose (8.3 mM)-induced insulin secretion in rat islet. In the presence of TsTx-V or veratridine, insulin secretion increased 2- and 1.4-fold over basal values, respectively (P<0.001). The Na+ channel antagonist tetrodotoxin (6 μM) significantly decreased glucose- and TsTx-V-induced insulin secretion (P<0.001). TsTx-V also stimulated insulin secretion at low glucose concentrations (2.8 mM) whereas the β-toxin, Ts-γ (gamma toxin), also obtained from Tityus serrulatus venom, significantly reduced TsTx-V-induced secretion at sub- and suprathreshold concentrations of glucose. These results are consistent with a model whereby Na+ channels participate in glucose-induced electrical activity. Alteration in the activity of these channels changes the length of time during which the β-cell depolarizes, thereby altering the secretory behavior of the cell. The construction of a three-dimensional model for TsTx-V revealed a conserved core containing an α-helix and three β-strands, with minor differences when compared with toxins from other scorpion venoms.

Thiopental inhibits K+ permeability of rat and mouse pancreatic β-cells

Abstract The effects of thiopental on the insulin release and 86 Rb efflux from isolated rat islets and on parameters of the electrical activity of single β-cells of mice were studied. Thiopental 0.2 and 1.0 mM increased by 16.6 and 33.3%, respectively, the insulin release induced by 6.0 mM glucose. Thiopental reduced the 86 Rb efflux rate in both 0 and 6.0 mM glucose, but had only a slight effect in 16.7 mM glucose. Menadione (20 μM) did not block the inhibitory effect of thiopental on 86 Rb efflux. Thiopental induced a reversible membrane depolarization in a dose-dependent manner (0.2-1.0 mM). It also induced electrical activity at a subthreshold glucose concentration and continuous spiking in presence of 11.1 mM glucose. In the presence of 2,4-dinitrophenol (20 μM) this continuous spiking was changed to an oscillatory activity similar to that induced by 11.1 mM glucose. Thiopental (0.5 mM) induced an increase in input resistance of 12.7, 17.9 and 16.0% in 0, 5.6 and 11.1 mM glucose, respectively . The thiopental-induced changes in insulin secretion, 86 Rb efflux and electrical parameters indicate that K + permeability was affected in both rat and mouse β-cells. Our results suggest that thiopental is a direct inhibitor of the glucose-sensitive K + permeability in the β-cell.

Oxygen uptake by Typhlonectes compressicaudus related to the body weight

1. 1. Oxygen consumption by Typhlonectes compressicaudus has been determined in aerial conditions and under obligatory submersion at 25°C. 2. 2. The O2 uptake by skin and lungs can be expressed as related to the body weight according to the equation: Vo2(ml/hr) = 0.120 W0.782. The correlation coefficient is 0.932. 3. 3. In animals submersed in O2 satured tapwater the relationship between O2 uptake and body weight can be determined by the equation: Vo2(ml/hr) = 0.118 W0.496. The correlation coefficient is 0.972. 4. 4. T. compressicaudus, is a typical aquatic Gymnophiona. In spite of a predominant aerial respiration, it can resist up to 40 min submersed in the aquaria, under normal conditions, and up to 120–150 min in the Schliepers respirometer.

Metformina interage com o treinamento físico diminuindo a glicemia e aumentando o armazenamento de glicogênio em ratos diabéticos

INTRODUCTION: Like in humans, lower amounts of glycogen are present in tissues of diabetic rats. However, training or drugs that lower glycemia can improve the metabolic control. Metformin increased glycogen while decreased glycemia in normal rats stressed by exercise. OBJECTIVE: In this work we investigated if regular exercise and metformin effects improve the metabolism of diabetic rats. METHODS: Alloxan diabetic Wistar rats treated with metformin (DTM) or not (DT) were trained. Training consisted of 20 sessions of 30 min, 5 days a week. Sedentary diabetic rats served as control (SD and SDM). Metformin (5.6 µg/g) was given in the drinking water. After 48 h resting, glucose (mg/dl) and insulin (ng/mL) was measured in plasma and glycogen (mg/100 mg of wet tissue) in liver, soleus and gastrocnemius. RESULTS: Glycemia decreased in DM group from 435±15 to 230±20, in DT group to 143±8.1 and in DTM group to 138±19 mg/dl. DM group had proportional increase in the hepatic glycogen from 1.69±0.22 to 3.53±0.24, and the training increased to 3.36 ± 0.16 mg/100 mg. Metformin induced the same proportional increase in the muscles (soleus from 0.21±0.008 to 0.42±0.03 and gastrocnemius from 0.33±0.02 to 0.46±0.03), while the training promoted increase on gastrocnemius to 0,53 ± 0,03, only. A high interaction was observed in liver (glycogen increased to 6.48±0.34). CONCLUSION: Very small oral doses of metformin and/or, partially restored glycemia in diabetic rats and decreased glycogen in tissues. Its association with an exercise program was beneficial, helping lower glycemia further and increase glycogen stores on liver of diabetic rats.