Rhythm of the β-cell oscillator is not governed by a single regulator: multiple systems contribute to oscillatory behavior

Abstract

Pulsatile insulin output, paralleled by oscillations in intracellular Ca2+, reflect oscillating metabolism within β-cells in response to secretory fuels. Here we question whether oscillatory periodicity is conserved or varied from stimulation to stimulation, whether glycolysis is essential for the manifestation of an oscillatory response, and if an environment of nutrient oversupply affects oscillatory regularity. We have determined that a β-cell oscillatory Ca2+ pattern is independent of the type of applied secretory fuel (glucose, methyl-pyruvate, or α-ketoisocaproate). In addition, single cells respond with the same pattern when repeatedly stimulated, regardless of the type of stimulatory fuel. Presence of substimulatory glucose is not necessary to obtain an oscillatory responses to methyl-pyruvate or α-ketoisocaproate. Glucose-6-phosphate, as a measure of glycolytic flux, is not detectable under these conditions. These data suggest that multiple systems, rather than a single enzyme component, can contribute to the β-cell oscillatory behavior. Prolonged exposure to high levels of palmitate impaired oscillatory regularity in the individual β-cells. This supports the hypothesis that a high-fat environment might contribute to loss of regular oscillatory pattern in diabetic subjects, acting, at least in part, at the level of the single β-cell.