Effect of fixation conditions on the granule morphology of rat antral gastrin cells: an ultrastructural and immunocytochemical study.

After fixation at pH = 7 or pH = 5 the gastrin (G) cells in the rat pyloric antrum were investigated by conventional and immunoelectron microscopy. After fixation at pH = 7 G cells contained numerous electron-lucent granules, a few electron-dense and intermediate granules while G cells had numerous electron-dense and intermediate granules, and a few electron-lucent granules after fixation at pH = 5. Preembedding immunoelectron microscopy revealed that in G cells after fixation at pH = 7, gastrin immunoreactivity was mainly seen in the cytoplasm, cores of a few electron-dense and intermediate granules and in the periphery but not within the numerous electron-lucent granules; in G cells after fixation at pH = 5, gastrin immunoreactivity was mainly visible in the cores of numerous intermediate and electron-dense granules, in the periphery of a few electron-lucent granules, but weakly in the cytoplasm. Therefore, the variable electron density of G cells may reflect differences in the degree of the leakage of contents from the gastrum-containing granules into the cytoplasm during fixation. This phenomenon may be related to the acidity of the granule substances during intragranular maturation.