AJP - Gastrointestinal and Liver Physiology, Vol 260, Issue 3 464-G470, Copyright © 1991 by American Physiological Society
Characteristics of luminal bicarbonate secretion by rat cecum in vitro
P. Canfield
Department of Physiology and Biophysics, St. Mary's Hospital Medical School, London, United Kingdom.
Under in vitro conditions the rat cecum transported HCO3- from the serosal
to an unbuffered solution in contact with the mucosal side [Js----m = 7.12
+/- 0.18 mumol.cm-2.h-1 (n = 149)]. With reversed tissues, a significantly
lower flux was obtained [Jm----s = 2.47 +/- 0.11 mumol.cm-2.h-1 (n = 42)].
Both fluxes were stable for several hours. Increasing the H+ gradient
across the tissue for 60 min did not change either flux. Anoxia for 45 min
reversibly reduced Js----m by 65 +/- 3% (n = 20) but had no effect on
Jm----s. Both fluxes were linearly related to HCO3- concentration on the
buffered side, but the slope for Js----m was 3.5 times that for Jm----s.
When tissues were initially set up in HEPES buffer rather than HCO3-,
Js----m was 0.12 +/- 0.05 mumol.cm-2.h-1 (n = 6), which is not
significantly different from zero. Replacement of Na+ by choline reduced
Js----m by 40 +/- 3% (n = 11) and ouabain (1 mM) by 24 +/- 3% (n = 5).
Replacement of Cl- with isethionate or K+ with Na+ for 60 min did not alter
Js----m. Serosal application of DIDS (0.5 mM) reduced Js----m by 24 +/- 6%
(n = 6), but SITS (0.5 mM), furosemide (1 mM), acetazolamide (0.1 mM),
amiloride (1 mM), and a proton pump inhibitor (Sch 28080, 50 microM) had no
effect. Mucosal application of DIDS, furosemide, and amiloride had no
effect on Js----m. Serosal tetrodotoxin (1 microM) and indomethacin (28
microM) were also without effect.(ABSTRACT TRUNCATED AT 250 WORDS)
