Sustained glucose-stimulated insulin secretion in mouse islets is not culture-dependent

Excerpt

To the Editor: The process of sustained glucose-evoked insulin secretion has been extensively studied, although the molecular mechanisms implicated are still poorly understood. Biphasic insulin release, and more specifically its associated second phase, is a subject of long-standing and intensive research [1]. In this context, it is intriguing that the dynamics of insulin secretion in a mouse model differ, depending on which of two widely used experimental preparations are employed. Using in situ pancreatic perfusion, glucose-stimulated insulin release is essentially monophasic, with a very weak second phase following the 4- to 5-min first phase [2, 3]. In contrast, once isolated, pancreatic islets exhibit sustained secretory responses to glucose in a perifusion protocol. How the mouse beta cell can switch from the transient (in situ) to the sustained (in vitro) secretory mode is unknown. Investigators commonly keep the islets in culture between the isolation procedure and perifusion experiments. This suggests the possibility that culture conditions might induce changes in gene expression and/or enzyme activity, thereby modifying the machinery of metabolism-secretion coupling. For instance, glucokinase activity is induced in mouse islets cultured at high glucose [4]. Such culture-dependent changes are supposed to modify glucose metabolism, thereby promoting signal generation implicated in the sustained phase of insulin release. Here, we questioned the effects of culture periods on the secretory profiles of isolated mouse islets in response to glucose stimulation. …