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Epithelial Hypertrophy; Intestinal Absorption; Na+-K+-ATPase; Rat Cecum; Sodium Transport Stimulation
Abstract:
The rat cecum is suitable to study ion transport in a hypertrophying mammalian epithelium. When the nonabsorbable polymer polyethylene glycol 4000 was added to the drinking water of adult rats, the gross surface area and dry weight of the cecum increased continuously over a period of two months. In contrast, an observed stimulation of sodium and volume transport rate per unit cecal area or weight reached its maximum within one week. In the absence of net salt and volume transport (stationary state), the transmural concentration difference for sodium and chloride but not for potassium was higher following hypertrophy, and the lumen was electrically more negative. Furthermore, hypertrophy was accompanied by an increase in Na+-K+-ATPase activity per unit area, weight or protein while other enzymes in cecal mucosa homogenates remained unaltered. Sodium and chloride were transported out of the lumen, and potassium secreted into the lumen, against an electrochemical potential difference in both the normal and hypertrophying cecum. The consideration of electrochemical driving forces and fluxes along with the enzymatic findings suggest that the stimulation of active sodium transport was the prominent functional change connected with cecal hypertrophy.
