Fresh and cultured mouse islets differ in their response to nutrient stimulation

Area of Science:

• Endocrinology
• Cell Biology
• Metabolism

Background:

• Insulin secretion is crucial for glucose homeostasis.
• Understanding stimulus-secretion coupling in pancreatic islets is key to diabetes research.
• Islet culture conditions can alter cellular function and responsiveness.

Purpose of the Study:

• To compare nutrient-induced insulin secretion kinetics between fresh and cultured mouse islets.
• To investigate differences in stimulus-secretion coupling parameters.
• To explore the impact of culture conditions on islet function.

Main Methods:

• Perifusion of freshly isolated and 22-h-cultured NMRI mouse islets.
• Stimulation with glucose, alpha-ketoisocaproic acid, tolbutamide, and KCl.
• Measurement of insulin secretion rates.
• Assessment of cytosolic Ca2+ concentration and ATP/ADP ratio.
• Monitoring of mitochondrial reducing equivalents (NAD(P)H/FAD fluorescence).

Main Results:

• Cultured islets exhibited a typical biphasic insulin secretion pattern, while fresh islets showed a continuously ascending rate with glucose.
• Both fresh and cultured islets responded similarly to non-nutrient secretagogues (tolbutamide, KCl).
• Cultured islets displayed a larger glucose-induced rise in cytosolic Ca2+ and ATP/ADP ratio, with altered mitochondrial activity.
• Modifying culture media resulted in variable insulin release but consistently predominant first-phase kinetics.

Conclusions:

• Nutrient-induced insulin secretion kinetics are more variable in fresh mouse islets than in cultured islets.
• The uniform kinetics in cultured islets might be due to altered endogenous metabolite utilization.
• These findings highlight the impact of culture on islet function and responsiveness.