The membrane surfaces of the toad bladder: Scanning and transmission electron-microscopy

Summary

The SEM permits analysis of large areas of the surface of epithelia and facilitates the study of cell-to-cell relationships, as pointed out by Fenguson and Heap (Z. Zellforsch.109:297, 1970). The short method of preparation described here yields good results when the critical point method is used for drying (freeze-drying was less satisfactory). Cell counts reveal that theBufo marinus toad bladder epithelium contains 3 or 4 granular (GR) cells to 1 mitochondria-rich (MR) cell. Whether these cell membrane contacts are permeable to the diffusion of high energy compounds and whether the MR cells serve as a source of energy for the GR cells are hypotheses that require further study. In view of the wide variations in the cell number per unit area even in single hemibladders, experimental measurements should probably be expressed either in terms of cell counts of DNA content, rather than per unit surface area.