AJP - Cell Physiology, Vol 256, Issue 4 C849-C857, Copyright © 1989 by American Physiological Society
Ultrastructure of Amphiuma distal nephron: evidence for cellular heterogeneity
D. Biemesderfer, B. Stanton, J. B. Wade, M. Kashgarian and G. Giebisch
Department of Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
To obtain more information on the ultrastructure of the distal nephron of
the salamander, Amphiuma, we conducted freeze-fracture electron microscopy
and morphometric experiments. In the early distal tubule, the organization
of the tight junction is variable, containing from one to two strands in
the proximal region and four strands in distal regions. The length density
of the tight junction in this segment varies from greater than 60 m/cm2 of
apical membrane surface to less than 10/cm2 of apical membrane surface.
These observations agree with a previous study demonstrating that the
junction of this segment exhibits considerable axial heterogeneity. The
junctions of the late distal tubule and collecting tubule are more complex.
In the late distal tubule, the tight junction is composed of 6-8 strands,
whereas the tight junction of the collecting tubule is composed of 8-12
strands. The collecting tubule contains principal cells and two types of
intercalated cells: alpha and beta. The alpha-cells contain a high density
of rod-shaped particles in the apical plasma membrane and in membranes of
apical cytoplasmic vesicles. The beta-cells contain rod-shaped particles
only in the basolateral membrane. In principal cells, we observed a novel
organization of intramembranous particles within the apical plasma
membrane. A model describing the relationship of the two types of
intramembranous particles within the membrane is presented. This study
demonstrates that the amphibian and mammalian distal nephron share many
morphological characteristics including cellular and axial heterogeneity.
