AJP - Gastrointestinal and Liver Physiology, Vol 248, Issue 1 54-G60, Copyright © 1985 by American Physiological Society
Colonic glycoprotein secretion and calmodulin-acceptor proteins in the reserpine-treated rat
R. C. Brady, K. J. Karnaky Jr and J. R. Dedman
The rate of radioactive precursor-labeled colonic glycoprotein secretion in
chronically reserpine-treated versus saline-injected control rats was
examined. Everted colonic sacs prepared from reserpine-treated rats were
found to be hypersecretory, exhibiting a basal rate of glycoprotein
secretion that was threefold higher than control everted sacs. Furthermore,
glycoprotein secretion in control tissue was stimulated by the secretagogue
carbachol, and this stimulation was precluded by 10 microM trifluoperazine,
the calmodulin antagonist. Reserpine-treated tissue, in contrast, was
refractory to treatment with carbachol as well as trifluoperazine. While
reserpine-treated and control colonic mucosae were demonstrated to contain
equivalent levels of calmodulin via radioimmunoassay, reserpine-treated
tissue was determined to lack two calmodulin-acceptor proteins with
molecular weights of 29 and 47 kilodaltons. The data suggest that the
mechanism by which reserpine elicits this cystic fibrosislike,
hypersecretory state of glycoprotein secretion within the colonic mucosa
entails the loss of calmodulin function in the regulation of this secretory
process. We speculate that the biochemical defect present in cystic
fibrosis could also entail such a loss of calmodulin function in the
regulation of glycoprotein secretion.
