Comparison of analytic techniques: chemical, isotopic, and microprobe analyses.

The development of new techniques and modifications to existing methods are providing important information about cellular water and electrolytes in relation to transepithelial transport. Information obtained for one epithelium, the toad urinary bladder, from chemical analyses, isotopic studies, and electron microprobe analysis, is reviewed. Chemical and isotopic analyses allow estimation of average cellular water and ion contents and determination of the origin of ions from the media bathing the mucosal and basolateral cellular membranes. The electron microprobe provides additional information about the distributions of ions between the cell types that constitute the epithelial layer and also allows some measurement of ion distributions within individual cells. In toad urinary bladder epithelial cells there is broad agreement between the results obtained with these different techniques and a summary is provided of possible relationships between transepithelial sodium transport and cellular composition.