The prevalence of strands shown by freeze-fracture in the zonula
occludens of junctional complexes is thought to correspond closely with the
transepi-thelial electrical resistance and with the tightness of the
junction and its obstruction to paracellular flow.1 The complexity of the
network of junc¬tional complex strands does not appear invariably related to
the degree of tightness of the junction, however, as rabbit ileal junctions
have a complex network of strands and are permeable to lanthanum. In human
eccrine sweat glands the extent of paracellular relative to transcellular
flow remains unknown, both for secretion of the isotonic precursor fluid by
the coil and for resorption of a hypertonic solution by the duct. The
studies reported here undertook, therefore, to determine with the
freeze-fracture technique the complexity of the network of ridges in the
junctional complexes between cells in the secretory coil and the sweat
ducts. Glands from a patient with cystic fibrosis were also examined because
an alteration in junctional strands could underlie the decreased Na+
resorption by sweat ducts in this disease. Freeze-fracture replicas were
prepared by standard procedures on isolated coil and duct segments of human
sweat glands. Junctional complexes between clear cells, between dark cells
and between clear and dark cells on the main lumen, and between clear cells
on intercellular canaliculi of the coil con¬tained abundant anastomosing
closely spaced strands averaging 6.4 + 0.7 (mean + SE) and 9.0 +0.5 (Fig. 1)
per complex, respectively. Thus, the junctions in the intercellular
canaliculi of the coil appeared comparable in complexity to those of tight
epithlia. Occasional junctions exhibited, in addition, 2 to 5 widely spaced
anastomosing strands in a very close network basal to the compact network.
The fewer junctional complexes observed thus far between the superficial
duct cells consisted on the average of 6 strands arranged in a close network
and 1 to 4 underlying strands that lay widely separated from one another
(Fig. 2). The duct epitelium would, thus, be judged slightly more "leaky"
than the coil. Infrequent junctional complexes observed to date in the
secretory coil segment of a cystic fibrosis specimen disclosed rela¬tively
few closely crowded strands.
Cystic Fibrosis in Egyptian Children: Achievements and Future Directions
