Sodium-coupled amino acid and sugar transport byNecturus small intestine |
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Authors: | Pamela J Gunter-Smith Etienne Grasset Stanley G Schultz |
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Institution: | (1) Department of Physiology and Cell Biology, University of Texas Medical School at Houston, 77025 Houston, Texas;(2) Present address: Department of Physiology, Armed Forces Radiobiological Research Institute, National Naval Medical Center, 20014 Bethesda, Maryland;(3) Present address: INSERM U83, Hôpital Herold, Place Rhin et Danube, F 75019 Paris, France |
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Abstract: | Summary
Necturus small intestine actively absorbs sugars and amino acids by Na-coupled mechanisms that result in increases in the transepithelial electrical potential difference (
ms
) and the short-circuit current (I
sc) which can be attributed entirely to an increase in the rate of active Na absorption. Studies employing conventional microelectrodes indicate that the addition of alanine or galactose to the mucosal solution is followed by a biphasic response. Initially, there is a rapid depolarization of the electrical potential difference across the apical membrane (
ms
) which reverses polarity (i.e. cell interior becomes positive with respect to the mucosal solution) and a marked decrease in the ratio of the effective resistance of the mucosal membrane to that of the serosal membrane (R
m
/R
s
); these events do not appear to be dependent on the availability of metabolic energy. These initial, rapid events are followed by a slow increase in (R
m
/R
s
) toward control values which is paralleled by a repolarization of
ms
and increases in
ms
andI
sc; this slow series of events is dependent upon the availability of metabolic energy.The results of these studies indicate that: (i) the Na-coupled mechanisms that mediate the entry of sugars and amino acids across the apical membrane are rheogenic (conductive) and result in a decrease inR
m
and a depolarization of
ms
; and (ii) the subsequent increase in (R
m
/R
s
) and repolarization of
ms
are the results of a decrease inR
s
which is associated with an increase in the activity of the Na pump at the basolateral membrane.The physiologic implications of these findings are discussed and an equivalent electrical circuit model for rheogenic Na-coupled solute transport processes is analyzed. |
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Keywords: | Necturus small intestine Na-coupled transport alanine galactose electrophysiology |
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