SODIUM-CHLORIDE TRANSPORT OF NORMAL AND DIETARY ENLARGED RAT CECUM IN-VITRO

Sodium chloride transport across isolated cecum mucosa was investigate d in normal rats and rats with adaptive cecum growth induced by dietar y polyethylene glycol (PEG). The normal cecum absorbed CI in excess of Na with a small short-circuit current (Isc). Dietary adaptation led t o large equivalent increments of Na and Cl net absorption without adeq uate Ise change. Inhibitor studies (mucosal amiloride 10(-3) and 10(-4 ) M; mucosal 4,4-diisolhiocyanatostilbene-2,2-disulfonic acid 5 x 10(- 5) M;serosal furosemide 10(-3) M;serosal ouabain 10(-3) M) suggested t hat normal cecal NaCl absorption involves electroneutral Na/N and Cl/H CO3 exchange at the apical and Na-K-ATPase-mediated exit across the ba solateral cell membrane. Dietary adaptation stimulates the loosely cou pled antiports and possibly activates a small serosally located NaCl c otransport. Comparative histology showed flattening of all tissue laye rs and widening of crypts in PEG animals. Crypt widening may facilitat e ion access to underutilized transport sites and, at least in part, e xplain the increased absorption of the enlarged cecum.