Increase in Gap Junctions in Frog Skin Epithelium

Abdominal frog skin, mounted on an Ussing chamber, actively transports sodium from the outer or pond side of the epithelium to the serosal side. The outermost layer of the skin is composed of cornified cells and does not participate in active transport. Pondside sodium enters through the first living layer of cells, the stratum granulosum. Electron microprobe studies demonstrated that the stratum granulosum and the more basal strata were in the route of sodium active transport. Previously we have shown, using frog skin processed immediately after euthanasia, that the stratum granulosum had significantly fewer gap junctions per unit length of membrane than the other strata. In this study we examined a time series of frog skins, from zero min to four h. Using an electron microscopic counting technique, we then determined the number of gap junctions and desmosomes in each stratum. The density of gap junctions (number/micrometer of membrane) in the stratum granulosum rose from 0.04/μm to 0.13/μm 30 min after chamber mounting. During this period, the density of gap junctions in the other strata was nearly constant. We conclude that the number of gap junctions in frog skin changes during chamber mounting.