Ultrastructural and cytochemical characterization of cultured dogfish shark rectal gland cells. Valentich, John D., Karl J. Karnaky, and Tom W. Ecay. Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX 77555-0564, Department of Cell Biology and Anatomy and the Marine Biomedical and Environmental Sciences Program, Medical University of South Carolina, Charleston, SC 29425, Department of Physiology, Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, Mount Desert Island Biological Laboratory, Salsbury Cove, ME 04672
APStracts 3:0229C, 1996.
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 non -epithelial 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 non-tubular 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 comprised 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 secretagogue effects on transport activity reflect their direct interaction with tubular epithelial cells. 

Received 33 March 1996; accepted in final form 26 June 1996.
APS Manuscript Number C136-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996