Scanning EM Studies of Gastric Oxyntic Cells with Special Reference to the Translocation of Tubulovesicular System towards the Intracellular Canaliculus

The membrane systems of the rat and frog oxyntic cells were examined by ultra-high-resolution SEM. Using a recently developed favorable fixation technique for parietal cells by Sugai et al. (20), rat gastric mucosae were microwave fixed in a cacodylate buffer, 334 milliosmoles/kgH2O (mOsm), to which 1.0% glutaraldehyde and 0.5% formaldehyde were added. Specimens examined by TEM of thin sections showed the cytoplasm packed with tubular membranes similar to images found after rapid-freeze/freeze-substitution fixation, which is generally considered to cause minimal structural alterations. To render the cytoplasmic membranes visible by SEM, fixed mucosae were frozen, fractured and macerated by the A-ODO procedure. With much of the cell matrix and filaments removed, SEM revealed numerous 30–60 nm tubules formed a three-dimensional network with small cisternae about 100 nm in diameter having a small fenestration at their center. This network was designated the “tubulocisternal network (TCN)”. The TCN occasionally connected with the rough-ER and the Golgi apparatus. Vesicles or isolated tubules were not found in appropriately macerated parietal cells. The intracellular canaliculus (IC) was lined with numerous microvilli. In favorable sites connections of the TCN to the IC were clearly visible. In the frog oxyntic cells, the TCN were more frequently connected with the luminal membrane than in the rat parietal cells. Connections between these two membrane compartments suggest the probability of rapid membrane transposition.