Phase-dependent differences in insulin secretion and oxygen consumption due to inhibition of protein biosynthesis by cycloheximide in mouse islets

 

Background and aims:

The hypothesis was tested that stimulation of protein biosynthesis contributes to the pattern of insulin secretion and oxygen consumption rate (OCR) during glucose-stimulated insulin secretion.

Methods:

NMRI mouse islets were used either freshly isolated or after overnight culture in RPMI with 10% FCS and 5 mM glucose. OCR kinetics and kinetics of insulin secretion were determined simultaneously from the same batch of continuously perifused islets.

Results:

Increasing the glucose concentration from 5 to 25 mM resulted in a prompt and strong increase of OCR, reaching a plateau after 20 min. After 40 min, a moderate continuous increase in OCR set in which continued until the wash-out of glucose. The concomitant increase of insulin secretion showed a modest first phase and continued steadily in second phase up to 61 pg/(islet x min). When the translation inhibitor cycloheximide was present, the initial OCR increase was less steep and no further increase occurred after the plateau was established. The concomitant increase in insulin secretion showed a minor difference to the control during first phase, but was significantly less extensive in second phase (35 pg/(islet x min)). Irrespective of the presence of cycloheximide, no further increase of OCR was noted in cultured islets.

Conclusion:

The continuous second phase increase in insulin secretion in response to glucose involves a further increase of oxygen consumption and is less extensive when protein biosynthesis is inhibited. This may reflect that second phase insulin secretion is influenced by the activation of protein biosynthesis in fresh islets.