Coupling ratio of electrogenic Na+-alanine cotransport in isolated rat hepatocytes

Kristensen, Lars Østergaard; Folke, M.

doi:10.1042/bj2100621

Cited by 19 publications

(9 citation statements)

References 12 publications

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“…Similarly the release of K from pre-loaded rabbit enterocytes is best described by a single decreasing exponential. The rate constant for this efflux was of the same order of magnitude as that reported for other isolated cells (Kristensen, 1980;Valdeolmillos, Garcia-Sancho & Herreros, 1982). Similar kinetic values for uptake and efflux were obtained using 42K and 86Rb as tracers, validating the use of the more convenient 86Rb isotope in future studies.…”

Section: Cell Viabilitysupporting

confidence: 69%

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

Brown¹,

Sepúlveda²

1985

The Journal of Physiology

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SUMMARY1. A method is described for isolating viable enterocytes from rabbit jejunum. Estimates of sucrase and y-glutamyl transferase activities in cells isolated by this method suggest that they originate from the upper villus only.2. Isolated cells accumulate both oc-methyl-D-glucoside and alanine, maintaining high intracellular concentrations for at least 60 and 40 min respectively. Accumulation of a-methyl-D-glucoside is inhibited by the presence of phloridzin.3. The cells accumulate 42K and 86Rb in an identical manner. This uptake, which is maintained for at least 60 min, is inhibited in the presence of ouabain. Passive efflux of 42K and 86Rb occurs with rate constants which are virtually identical. The efflux follows a single exponential suggesting that it originates from only one intracellular compartment.4. It is suggested that the preparation can be used to study the effect of sugars and amino acids on K efflux. The advantages of using such a preparation are discussed.

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Section: Cell Viabilitysupporting

confidence: 69%

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

Brown¹,

Sepúlveda²

1985

The Journal of Physiology

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“…Kristensen (1980) has demonstrated an increase in K permeability of isolated rat hepatocytes associated with Na-coupled alanine uptake and has drawn the same conclusion.…”

supporting

confidence: 61%

Effects of Na-coupled alanine transport on intracellular K activities and the K conductance of the basolateral membranes ofNecturus small intestine

Grasset¹,

Gunter-Smith²,

Schultz³

1983

J. Membrain Biol.

103

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Intracellular electrical potentials and K activity, (K)c, were determined simultaneously in Necturus small intestine before and after the addition of alanine to the mucosal solution. As noted previously (Gunter-Smith, Grasset & Schultz, 1982), the addition of alanine to the mucosal solution resulted in a prompt depolarization of the electrical potential difference across the apical membrane (psi mc) and a decrease in the slope resistance of that barrier (rm). This initial response was followed by a slower repolarization of psi mc associated with a decrease in the slope resistance of the basolateral membrane (rs) so that when the steady state was achieved (rm/rs) did not differ significantly from control values in the absence of alanine. In the absence of alanine, psi mc averaged -32 mV and (K)c averaged 67 mM. When a steady state was achieved in the presence of alanine these values averaged -24 mV and 50 mM, respectively. The steady-state electrochemical potential differences for K across the basolateral membrane in the absence and presence of alanine did not differ significantly. Inasmuch as the rate of transcellular active Na transport or "pump activity" was increased two- to threefold in the presence of alanine, it follows that, if active Na extrusion across the basolateral membrane is coupled to active K uptake across that barrier with a fixed stoichiometry then, the decrease in rs must be due to an increase in the conductance of the basolateral membrane to K that parallels the increase in "pump activity". This "homocellular" regulatory mechanism serves to (i) prevent an increase in (K)c due to an increase in pump activity; and, (ii) repolarize psi mc and thus restore the electrical driving force for the rheogenic Na-coupled entry processes.

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“…Higgins, Gebler and Fr6mter (1977) arrived at the same conclusion for the case of Necturus urinary bladder and suggested that this could be explained "... if the passive K-leak permeability were an inherent property of the Na-K pump unit or were regulated by an intracellular feedback mechanism." Recently, Kristensen (1980) has reported that rheogenic Na-alanine co-transport by isolated rat hepatocytes is associated with a fivefold increase in the permeability of the hepatocyte membrane to K and no significant change in cell K content. Indeed, Lee and Armstrong (1972) reported that the intracellular K activity, (K)c, in bullfrog small intestine determined using ion-selective microelectrodes decreased following addition of 3-O-methylglucose to the mucosal solution, and, using similar methods, White (1976) has reported that (K)c in Amphiuma small intestine is the same in the presence and absence of 10raM glucose; although the rate of Na absorption was not measured in these studies, it is fair to assume that it was increased in the presence of these sugars (Schultz, 1977).…”

Section: The Relation Between the "Pump" And "Leak" Properties Of Thementioning

confidence: 99%

Sodium-coupled amino acid and sugar transport byNecturus small intestine

Gunter-Smith¹,

Grasset²,

Schultz³

1982

J. Membrain Biol.

131

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Necturus small intestine actively absorbs sugars and amino acids by Na-coupled mechanisms that result in increases in the transepithelial electrical potential difference (r and the short-circuit current (I~c) 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 (r 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'~ 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 (Rm/R ~) toward control values which is paralleled by a repolarization of ~,mc and increases in ~,,s and I~c; 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 in R m and a depolarization of Omc; and (ii) the subsequent increase in (R"/R') and repolarization of O,~c are the results of a decrease in R ~ 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" Nacoupled solute transport processes is analyzed.

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Coupling ratio of electrogenic Na+-alanine cotransport in isolated rat hepatocytes

Cited by 19 publications

References 12 publications

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

Effects of Na-coupled alanine transport on intracellular K activities and the K conductance of the basolateral membranes ofNecturus small intestine

Sodium-coupled amino acid and sugar transport byNecturus small intestine

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