Insulin intracellular mediator

Our understanding of the details of these processes will probably increase in the near future, due to the development of better techniques for the determination of intracellular [Ca2+], One example involves the use of the fluorescent indicator quin 2. This allows quantitative determination of [Ca2+] rather than the mere confirmation of increase or decrease in [Ca2+].412,413 Quin 2 binds Ca2+ with high selectivity, and its fluorescence increases more than four-fold upon saturation with Ca2". The indicator is added in a lipophilic form, the tetraacetoxymethyl ester, which is taken up by cells. Hydrolysis within the cells gives quin 2, which will then remain in the cell cytosol without binding to cytoplasmic proteins or uptake into organelles. An example of its use lies in the demonstration that release of insulin was mediated by increase in cytosolic Ca2+ produced by use of the Ca2+-ionophore ionomycin.414... 

As one would expect, for all its elegance, this model does not exhaust the potential functions of calcium-independent PLA2S. Evidence tallies also with a direct participation of this enzyme in arachidonate mobilization in pancreatic p cells, for example, an ATP-activated, heart-type isoform of calcium-independent PLA2 may mediate mobilization of arachidonate and subsequent formation of 12-lipoxygenase metabolites, which are thought to act as intracellular mediators in glucose-induced insulin secretion. 

To prevent insulin-mediated intracellular shift of potassium during the infusion... 

Figure 5.6. Metabolism of proteins by proteases found at the cell surface and internal cellular organelles. Intracellular uptake of proteins often involved receptor-mediated endocytosis initial surface binding can be specific for a hormone (e.g., insulin, glucagon).

Internalization of protein hormones is a principal means of hormone degradation in lysosomes through a receptor-mediated pathway [70], There may also be membrane-associated degradative activities for insulin (insulinase) and other protein hormones, however for EGF, degradation occurs exclusively through an intracellular process [68,71]. 

---