Mammalian tuft (brush) cells and chloride cells of other vertebrates sharea similar structure and cytochemical reactivities

The function of the tuft (brush) cells is still obscure. From the morpholog ical similarities between tuft cells and chloride cells in the fish gill, w hich secrete or absorb NaCl, it was hypothesized that mammalian tuft cells may share functional roles similar to chloride cells. To test this hypothes is, the following points were studied on rat tuft cells. 1) The ultrastruct ural changes of bile duct tuft cells after secretin stimulation showed a mo derate increase of basolateral membrane infoldings and a decrease of tubulo vesicles in the apical cytoplasm. 2) The ultrastructural changes of tuft ce lls in the gastric groove of the rats on a high NaCl diet for 4 weeks, whic h were directly exposed to a high NaCl diet, and showed a marked shortening of microvilli and an appearance of numerous large vacuoles in the cytoplas m. 3) Cytochemical demonstrations of chloride and sodium ions were analyzed by energy-dispersive X-ray microanalysis(EDX). Massive reaction products o f 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 t he tuft cells without stimulation. Reaction products of sodium were predomi nantly found along the basolateral membranes of tuft cells 5 min after secr etin stimulation, but they were absent along those of tuft cells without st imulation. 4) Immunohistochemical demonstration of Na+/(K)+-ATPase, which i s highly reactive in chloride cells of the fish gill, was positive in the t uft cell cytoplasm. These findings indicate that the mammalian tuft cells h ave properties similar to chloride cells in other vertebrates. By monitorin g the electrolyte concentration with their long microvilli. tuft cells may regulate concentrations of electrolytes, probably NaHCO3. in the secretory fluid of hollow organs.