Differing mechanisms of stimulation of na absorption in rabbit
proximal colon.
Sellin, Joseph H., and Roland Desoignie.
Division of Gastroenterology, Department of Internal Medicine, The
University of Texas Medical School at Houston, Houston, Texas
APStracts 3:0197G, 1996.
Background/Aims: Both [alpha]-2 adrenergic agonists and decreased [Na]
in the bathing fluids stimulate electroneutral Na absorption in
rabbit proximal colon, but it is unclear whether they have similar
modes of action. We sought to define regulatory events involved with
stimulation of Na absorption by these two agonists. Transport
parameters were assessed by ion flux studies under short-circuit and
pH stat conditions, recordings of intracellular potential difference
([omega]mc) with microelectrode impalements, and measurement of
intracellular pH. Epinephrine elicited a yohimbine-inhibitable
alkalinization of intracellular pH, but did not alter [omega]mc. In
contrast, lowered serosal [Na] did not significantly increase pHi but
did depolarize [omega]mc. Removal of serosal [HCO3] stimulated Na
absorption and reversed residual ion flux from secretion to
absorption. pH stat studies (JHCO3m-s) demonstrated epinephrine
-stimulated, amiloride-inhibitable serosal alkalinization. Serosal
DIDS inhibited Na absorption. Epinephrine and lowered [Na] have
different effects on intracellular parameters associated with
electroneutral Na absorption. Epinephrine stimulates an apical Na-H
exchanger. Lowered [Na] elicits responses consistent with a coupled
Na-HCO3(x) exit step. Coordinated function of apical Na-H exchangers
and a basolateral Na-HCO3(x) symport permit Cl-independent
electroneutral Na absorption while maintaining pHi homeostasis. Given
the low [Cl] environment of the colonic lumen, this transport pathway
may be important for electroneutral Na absorption.
Received 1 September 1995; accepted in final form 30 August 1996.
APS Manuscript Number G386-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996