AJP - Cell Physiology, Vol 271, Issue 6 C1993-C2003, Copyright © 1996 by American Physiological Society
Ultrastructural and cytochemical characterization of cultured dogfish shark rectal gland cells
J. D. Valentich, K. J. Karnaky and T. W. Ecay
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0564, USA. jdv@metamatrix.com
The dogfish shark rectal gland (SRG) is histologically complex, containing
connective, nerve, and smooth muscle tissue and at least three types of
epithelial cells: secretory tubule, central duct, and endothelial. This
cellular heterogeneity precludes studies of the intact SRG from
distinguishing direct tubular effects of mediators that modulate chloride
secretion from their indirect effects on nonepithelial cells such as
neurons. Primary SRG cultures express high levels of
secretagogue-stimulated chloride secretion, suggesting that SRG cells
retain a significant level of cytodifferentiation in vitro. However,
because nontubular cells could contaminate these cultures, the question of
whether secretagogues activate chloride secretion through direct or
indirect effects on tubular epithelial cells remains unresolved. To address
this issue, detailed ultrastructural and cytochemical analyses of SRG
cultures were carried out to assess the level of cellular heterogeneity and
the degree of cytodifferentiation expressed by SRG cells in vitro. The
results demonstrate that, after 15 days, primary SRG monolayer cultures are
composed exclusively of tubular epithelial cells with no detectable
contamination by central duct cells, fibroblasts, smooth muscle cells,
endothelial cells, or neurons. Tubular epithelial cells express most of the
structural features of native SRG cells, including numerous mitochondria,
massive basolateral surface amplification, complex tight junctions, and an
extensive tubulovesicular system in the apical cytoplasm. Cultured SRG
cells also display a striking level of polarization of cytoplasmic
organelles and plasma membrane secretagogue receptors. These results
account for the exceptionally high rates of electrogenic chloride secretion
by SRG tubular epithelial cells in vitro and confirm that the effects of
secretagogues on transport activity reflect their direct interaction with
tubular epithelial cells.
