Reduced Insulin Secretion in Protein Malnourished Mice Is Associated with Multiple Changes in the β-Cell Stimulus-Secretion Coupling

Abstract

The mechanism by which protein malnutrition impairs glucose-stimulated insulin secretion in the pancreatic beta-cell is not completely known but may be related to alterations in the signaling events involved in insulin release. Here, we aimed to study the stimulus-secretion coupling of beta-cells from mice fed with low-protein (LP) diet or normal-protein (NP) diet for 8 wk after weaning. Patch-clamp measurements in isolated cells showed that beta-cells from LP mice had a resting membrane potential that was more hyperpolarized than controls. Additionally, depolarization and generation of action potentials in response to stimulatory glucose concentrations were also impaired in beta-cells of LP mice. All these alterations in the LP group were most likely attributed to higher ATP-dependent K(+) (K(ATP)) channel activity in resting conditions and lower efficiency of glucose to induce the closure of these channels. Moreover, a Western blot analysis revealed higher protein levels of the sulphonylurea receptor of the K(ATP) channel in islets of LP mice. Because beta-cell Ca(2+) signals depend on electrical activity, intracellular Ca(2+) oscillations were measured by fluorescence microscopy in intact islets, indicating a lower response to glucose in the LP group. Finally, cell-to-cell synchrony of Ca(2+) signals was analyzed by confocal microscopy. Islets from LP mice exhibited a decreased level of coupling among beta-cells, which was probably due to the low expression levels of connexin 36. Therefore, low-protein diet leads to several alterations in the stimulus-secretion coupling of pancreatic beta-cells that might explain the diminished insulin secretion in response to glucose in this malnutrition state.

Involvement of ATP-sensitive Potassium (KATP) Channels in the Loss of Beta-cell Function Induced by Human Islet Amyloid Polypeptide

“…Cells were placed in a chamber mounted on the microscope stage and perfused at a rate of 1.5 ml/min with a modified Ringer's solution (33) containing glucose, KCl, or tolbutamide. Calcium records were obtained by imaging intracellular calcium under an inverted epifluorescence microscope as described previously (33). Fluorescence changes were expressed as the ratio of fluorescence at 340 and 380 nm (F 340 /F 380 ), and the increment of fluorescence (⌬F 340 /F 380 ) was obtained by subtracting the mean basal fluorescence levels in the absence of stimulus (2.8 mM glucose) from the fluorescence value during the stimulus (16.7 mM glucose, 30 mM KCl, or 100 M tolbutamide).…”

“…⌬ m was monitored using the same imaging system described in Ref. 33 with conventional fluorescein filters (34,35).…”

miR-124a expression contributes to the monophasic pattern of insulin secretion in islets from pregnant rats submitted to a low-protein diet

“…In contrast, a low-protein diet during the growth phase after weaning reduces the first phase of insulin secretion [5] and shifts the dose-response curve to the right [6]. These alterations are associated with the decrease of 45 Ca influx, an increase in K ATP channel activity in resting conditions, the inability of glucose to induce the closure of these channels [7], and reduced syntaxin 1A and SNAP-25 protein expression in pancreatic islets [8].…”

Exercise Causes Muscle GLUT4 Translocation in an Insulin-Independent Manner

“…Subsequent depolarization of the plasma membrane [37] then opens voltage-sensitive (L-type) Ca2+ channels [38] causing insulin containing vesicles to fuse at the plasma membrane [39]. The mechanisms that link changes in glucose concentration to the regulation of Β-cell genes are less well understood [40,41].…”