The effect of islet culture on the biphasic pattern of fuel-induced insulin secretion

Background and aims:

The insulin secretion pattern by mouse islets is reported to differ from that of human and rat islets in that a strong first phase is followed by an elevated plateau instead of a slowly ascending second phase. This has led to the argument that mouse islets or beta cells may not be a good experimental model. Here, we have tested the role of islet culture on shaping the kinetics of insulin secretion.

Methods:

Mouse islets were isolated by collagenase digestion and selected by hand-picking. The culture duration was 24h in RPMI with 10% FCS. The glucose concentration in the cuture medium was 5 mM. The kinetics of secretion was measured by islet perifusion and ELISA of the fractionated efflux.

Results:

Raising the glucose concentration from 0 to 30 mM produced a modest initial increase in insulin secretion of freshly isolated islets, which was followed by a continuous increase up to 100 pg x islet^-1 x min^-1. With cultured islets 30 mM glucose generated a marked first phase (70 pg x islet^-1 x min^-1) which after 15 min receded back to a moderately elevated plateau (25 pg x islet^-1 x min^-1). Fresh islets responded to 10 mM a-ketoisocaproic with a prompt, strong and sustained secretion, whereas cultured islets generated a pattern which closely resembled that of 30 mM glucose.

Conclusion:

Cell culture may not simply relieve the stress of collagenase isolation but may leave an imprint which profoundly affects the secretory response to fuel secretagogues.