Optical techniques for the evaluation of epithelial transport processes.

Light microscopic observation of living epithelial tissues is a powerful analytical tool in the investigation of solute and water transport. New techniques in quantitative microscopy permit the determination of epithelial cell size and shape as well as accurate measurements of lateral intercellular space dimensions. Traditional techniques for the study of epithelial cell function may be used in conjunction with continuous quantitation of tissue morphology. Fluorescent probes of membrane, cell, and interspace function may be monitored at low light levels to obtain information about the dynamic behavior of the preparation. Application of some of these methods to the Necturus gallbladder epithelium has enabled determination of lateral cell membrane compliance, the hydrostatic pressure equivalent to active transport, the intracellular NaCl transport pool, the rate of active NaCl transport, and the flux of NaCl into the cell across the apical membrane. Possible future applications of optical techniques include measurement of water permeability, solute reflection coefficients, fluid flow paterns, and interspace osmolality.