title: Lithium absorption in tight and leaky segments of intestine.
abstract: There is significant absorption of Li+ by human jejunum and ileum, but negligible absorption by human colon. Thus, a proximal-to-distal gradient of decreasing Li+ absorption and increasing junctional tightness exists in intestine as well as in renal tubule. For six leaky epithelia the relative permeabilities of K+, Na+, and Li+ by the junctional route are in the sequence PK greater than PNa greater than PLi and all fall within a factor of 2.5. In contrast, for tight epithelia PLi approximately PNa much greater than PK in the amiloride-sensitive channel of the apical membrane, but PK much greater than PLi approximately PNa in the basolateral membrane. The ability of several tight epithelia to sustain nonzero transepithelial Li+ absorption despite this basolateral barrier may be due to Na+/Li+ countertransport at the basolateral membrane, resulting in secondary active transport of Li+ across the epithelium.
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D008094:Lithium / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism; D011197:Potassium Radioisotopes; D012964:Sodium / Q000378:metabolism
chemical_list: D011197:Potassium Radioisotopes; D008094:Lithium; D012964:Sodium; D011188:Potassium