Lithium absorption in tight and leaky segments of intestine |
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Authors: | Jared M Diamond Barbara E Ehrlich Stephen G Morawski Carol A Santa Ana John S Dordtran |
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Institution: | 1. Department of Physiology, University of California Medical Center, 90024, Los Angeles, California 3. Department of Medicine, Baylor University Medical Center, 75246, Dallas, Texas
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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. |
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