Localization of bicarbonate transport along the crypt-villus axis in rabbit ileum.
OBJECTIVE
HCO3- can be absorbed as well as secreted in the rabbit ileum. With 25 mmol/L HCO3- on the serosal side only, a serosa-to-mucosa flux (Jsm) is found; with 25 mmol/L on the mucosal side only, epinephrine elicits a mucosa-to-serosa flux (Jms). This study aimed to localize these two processes along the crypt-villus axis.


METHODS
Excised ileal segments were exposed luminally to 2 mol/L Na2SO4 (hypertonic treatment) or to isotonic Ringer's solution for 15 minutes. Mucosa was then chamber-mounted, and measurements were made of Jsm or Jms and of short-circuit current (Isc) responses to glucose plus alanine and to either theophylline or epinephrine.


RESULTS
With HCO3-/CO2 added to the serosal side only, hypertonically treated tissues showed a 22% decline in Jsm; a 25% decline in Isc response to theophylline; and a 71% decline in Isc response to glucose plus alanine compared with control. With HCO3-/CO2 added to the mucosal side only, tissues showed 92% and 87% declines in Jms and Isc responses to epinephrine, respectively, and a 87% decline in Isc response to glucose plus alanine. Histological examination showed destruction of villus caused by hypertonic treatment but sparing of crypt cells.


CONCLUSIONS
Both HCO3- and Cl- are secreted mainly by crypt cells and absorbed mainly by villus cells.
Minhas
B S
BS
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York.
Field
M
M
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D004837:Epinephrine / Q000494:pharmacology; D006982:Hypertonic Solutions / Q000494:pharmacology; D007082:Ileum / Q000378:metabolism*; D066298:In Vitro Techniques; D008871:Microvilli / Q000378:metabolism; D009092:Mucous Membrane / Q000378:metabolism; D011817:Rabbits; D012704:Serous Membrane / Q000378:metabolism; D013806:Theophylline / Q000494:pharmacology; D014018:Tissue Distribution
D001639:Bicarbonates; D006982:Hypertonic Solutions; D013806:Theophylline; D004837:Epinephrine