Surface area ratios. I. A stereological method for estimating average cell changes in membrane surface areas.

The study (i) describes a method for estimating relative changes in membrane surface areas as they occur in stereological "average cells," and (ii) considers the effect of the controls on these estimates. The results indicate that changes in five membranes compartments of pancreatic exocrine cells--produced by a secretagogue (carbomylcholine chloride)--were detected similarly when related to either an average cell surface (surface area ratio method) or to an average cell volume (method of Loud, '68). Changes, however, detected with surface densities, which relate these membrane compartments to 1 cm3 of exocrine cell cytoplasm or pancreas, were notably different from the first two estimates. This inconsistency could be explained by the fact that the surface densities were influenced not only by membrane changes within the exocrine cells, but also by changes in the number of these cells filling the cm3 of reference volume. Relating the data to an average cell reference--instead of 1 cm3--improved the accuracy of the estimates for changes in membrane surface areas by as much as several fold; the choice of controls had a similar several-fold effect on the results.