Mammalian Tuft (Brush) Cells and Chloride Cells of Other Vertebrates Share a Similar Structure and Cytochemical Reactivities.

Abstract

The function of the tuft (brush) cells is still obscure. From the morphological similarities between tuft cells and chloride cells in the fish gill, which secrete or absorb NaCl, it was hypothesized that mammalian tuft cells may share functional roles similar to chloride cells. To test this hypothesis, the following points were studied on rat tuft cells. 1) The ultrastructural changes of bile duct tuft cells after secretin stimulation showed a moderate increase of basolateral membrane infoldings and a decrease of tubulovesicles in the apical cytoplasm. 2) The ultrastructural changes of tuft cells in the gastric groove of the rats on a high NaCl diet for 4 weeks, which were directly exposed to a high NaCl diet, and showed a marked shortening of microvilli and an appearance of numerous large vacuoles in the cytoplasm. 3) Cytochemical demonstrations of chloride and sodium ions were analyzed by energy-dispersive X-ray micro analysis (EDX). Massive reaction products of chloride were found in the apical cytoplasm of some tuft cells of fasting rats 5 min after secretin stimulation, but they were virtually absent in the tuft cells without stimulation. Reaction products of sodium were predominantly found along the basolateral membranes of tuft cells 5 min after secretin stimulation, but they were absent along those of tuft cells without stimulation. 4) Immunohistochemical demonstration of Na+/K+-ATPase, which is highly reactive in chloride cells of the fish gill, was positive in the tuft cell cytoplasm. These findings indicate that the mammalian tuft cells have properties similar to chloride cells in other vertebrates. By monitoring the electrolyte concentration with their long microvilli, tuft cells may regulate concentrations of electrolytes, probably NaHCO3, in the secretory fluid of hollow organs.