Fig. 3. Glycine (red) is found both in core and in mantle cells of the islet (A,B) and is co-localized with glucagon (green) in mantle cells (C). Electron microscopic immungold analysis (D) shows glycine (15 nm gold particles, red arrows) distribution in a B-cell (left) and an A-cell (right, double labelled with 10 nm gold particles representing glucagon, short arrows). Insets: high magnification examples of SLMVs (arrowheads) labelled for glycine in the two cell types. Quantification of immunogold particles (E-G) shows the intracellular distribution of glycine. Note that the numbers cannot be directly compared with those for GABA (Fig. 2), as the labelling efficiencies are not the same. The densities (number of 15 nm gold particles per µm², background over tissue-free plastic, ca 2 per µm², subtracted) of glycine immunoreactivity over SGs and residual cytoplasm (free of mitochondria and SGs), show that glycine occurs at higher concentrations in SGs than in the residual cytoplasm (P=0.05, n=5) both in A- and in B-cells (E). (F) In A-cells, SLMVs have higher net densities of glycine particles than cytosol, whereas in B-cells, cytosol has a higher net labelling density than SLMVs (subtraction as in Fig. 2G; P=0.005 for gross particle densities, n=4, for both A- and B-cells). However, owing to the small diameter of the SLMVs compared with the diameter in which the glycine gold particles are observed, the concentration of glycine inside A-cell SLMVs is about 15 times higher than in cytosol, whereas the concentration inside B-cell SLMVs is about 5 times higher than in cytosol (A greater than B at P=0.002) (G). Scale bar D: 200 nm (scale for insets: 15 nm gold particles).