| Abstrakt: |
A histochemical and electron microscopical study was conducted on the lime sacs of larval and adult Rana catesbiana. Both undecalcified and EDTA-decalcified material was analyzed. The follicles of the lime sacs contain numerous aragonite crystals and are lined by a cuboidal epithelium. The epithelial cells contain granules of a material identified histochemically as acid mucopolysaccharide. Crystals similar to those present in the lumen of the follicles were also found inside the epithelial cells. These cells possess nuclei with coarsely distributed chromatin, many mitochondria, free ribosomes, well developed Golgi complexes and a few profiles of rough endoplasmic reticulum. Numerous variously electron dense granules seem to correspond to those characterized histochemically as mucopolysaccharides. Large, intracellular vacuoles appear to contain crystals. Release of the crystals into the lumen seems to occur by apocrine secretion. Resorption of calcium from the lumen probably takes place by diffusion through the apical plasma membrane as indicated by the presence of numerous microvilli. The intercellular spaces contain numerous, thin, interdigitating processes from neighbouring cells and appear to be sealed at both ends by junctional complexes. This observation is discussed in relation to the idea that the intercellular spaces might be related to the transit of calcium from the epithelial cells towards the sub-epithelial capillaries. [ABSTRACT FROM AUTHOR] |
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