Potassium transport by rabbit descending colon

1982 ◽  
Vol 242 (1) ◽  
pp. C81-C86 ◽  
Author(s):  
R. McCabe ◽  
H. J. Cooke ◽  
L. P. Sullivan
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Paracellular Pathway ◽  
Potential Difference ◽  
Metabolic Energy ◽  
Sodium Absorption ◽  
Potassium Absorption ◽  
Potassium Secretion ◽  
Descending Colon

Unidirectional mucosal-to-serosal (Jm leads to s) and serosal-to-mucosal (Js leads to m) fluxes of potassium and sodium were determined simultaneously on paired sections of descending colon from the same rabbit under short-circuit conditions. In 13-16 pairs of tissues, net potassium secretion and sodium absorption averaged 0.49 +/- 0.08 and 4.0 +/- 0.8 mueq.cm-2.h-1, respectively. Short-circuit current (Jsc) averaged 3.7 +/- 0.4 mueq.cm-2.h-1 and was approximately equal to the algebraic sum of net potassium and sodium fluxes. Treatment of both sides of the colon with 10(-4) M ouabain reduced the Jsc and transmural potential difference to near zero. Ouabain abolished net potassium secretion by reducing JKs leads to m and abolished net sodium absorption by inhibiting JNam leads to s. In the presence of ouabain, net potassium absorption averaging 0.15 +/- 0.07 mueq.cm-2.h-1 (n = 11) was observed. In the presence of 10(-3) M 2,4-dinitrophenol, both net potassium and net sodium fluxes were abolished, primarily as a result of a reduction in JKs leads to m and JNam leads to s without altering JKm leads to s and JNas leads to m. These results suggest that the rabbit descending colon has the capacity to secrete and possibly to absorb potassium by active mechanisms requiring metabolic energy. Comparison of potassium and sodium fluxes suggest that the paracellular pathway in the rabbit colon is not potassium selective.

Corticosteroid alteration of active electrolyte transport in rat distal colon

1983 ◽  
Vol 245 (5) ◽  
pp. G668-G675 ◽  
Author(s):  
E. S. Foster ◽  
T. W. Zimmerman ◽  
J. P. Hayslett ◽  
H. J. Binder
Keyword(s):  
Colonic Mucosa ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Transport Processes ◽  
Electrolyte Transport ◽  
Sodium Absorption ◽  
Rat Distal Colon ◽  
Potassium Absorption ◽  
Potassium Secretion

To determine the effect of corticosteroids on active transport processes, unidirectional fluxes of 22Na, 36Cl, and 42K were measured under short-circuit conditions across isolated stripped distal colonic mucosa of the rat in control, secondary hyperaldosterone, and dexamethasone-treated animals. In controls net sodium and chloride fluxes (JNanet and JClnet) and short-circuit current (Isc) were 6.6 +/- 2.2, 7.6 +/- 1.6, and 1.3 +/- 0.2 mu eq X h-1 X cm-2, respectively. Although aldosterone increased Isc to 7.3 +/- 0.5 mu eq X h-1 X cm-2, JNanet (6.9 +/- 0.7 mu eq X h-1 X cm-2) was not altered and JClnet was reduced to 0 compared with controls. Dexamethasone also stimulated Isc but did not inhibit JClnet. In Cl-free Ringer both aldosterone and dexamethasone produced significant and equal increases in JNanet and Isc. Theophylline abolished JNanet in control animals but not in the aldosterone group. Aldosterone reversed net potassium absorption (0.58 +/- 0.11 mu eq X h-1 X cm-2) to net potassium secretion (-0.94 +/- 0.08 mu eq X h-1 X cm-2). Dexamethasone reduced net potassium movement to 0 (-0.04 +/- 0.12 mu eq X h-1 X cm-2). These studies demonstrate that 1) corticosteroids stimulate electrogenic sodium absorption and 2) aldosterone, but not dexamethasone, inhibits neutral NaCl absorption and stimulates active potassium secretion. The effects of mineralocorticoids and glucocorticoids on electrolyte transport are not identical and may be mediated by separate and distinct mechanisms.

Water and electrolyte transport by rabbit esophagus

1975 ◽  
Vol 229 (2) ◽  
pp. 438-443 ◽  
Author(s):  
DW Powell ◽  
SM Morris ◽  
DD Boyd
Keyword(s):  
Sodium Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Electrolyte Transport ◽  
Potential Difference ◽  
Sodium Absorption ◽  
Bathing Solution ◽  
Electrical Potential Difference

The nature of the transmural electrical potential difference and the characteristics of water and electrolyte transport by rabbit esophagus were determined with in vivo and in vitro studies. The potential difference of the perfused esophagus in vivo was -28 +/- 3 mV (lumen negative). In vitro the potential difference was -17.9 +/- 0.6 mV, the short-circuit current 12.9 +/- 0.6 muA/cm2, and the resistance 1,466 +/- 43 ohm-cm2. Net mucosal-to-serosal sodium transport from Ringer solution in the short-circuited esophagus in vitro accounted for 77% of the simultaneously measured short-circuit current and net serosal-to-mucosal chloride transport for 14%. Studies with bicarbonate-free, chloride-free, and bicarbonate-chloride-free solutions suggested that the net serosal-to mucosal transport of these two anions accounts for the short-circuit current not due to sodium absorption. The potential difference and short-circuit current were saturating functions of bathing solution sodium concentration and were inhibited by serosal ouabain and by amiloride. Thus active mucosal-to-serosal sodium transport is the major determinant of the potential difference and short-circuit current in this epithelium.

Refinements in the Short-Circuit Technique and its Application to Active Potassium Transport Across the Cecropia Midgut

1978 ◽  
Vol 77 (1) ◽  
pp. 123-140
Author(s):  
JOHN L. WOOD ◽  
ROGER B. MORETON
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Electrode System ◽  
Potassium Transport ◽  
Potential Difference ◽  
Electrode Spacing ◽  
Half Time ◽  
Bathing Medium ◽  
Larval Midgut

The conventional, two-electrode method for measuring potential difference across an epithelium is subject to error due to potential gradients caused by current flow in the bathing medium. Mathematical analysis shows that the error in measuring short-circuit current is proportional to the resistivity of the bathing medium and to the separation of the two recording electrodes. It is particularly serious for the insect larval midgut, where the resistivity of the medium is high, and that of the tissue is low. A system has been devised, which uses a third recording electrode to monitor directly the potential gradient in the bathing medium. By suitable electrical connexions, the gradient can be automatically compensated, leaving a residual error which depends on the thickness of the tissue, but not on the electrode separation. Because the thicknesses of most epithelia are smaller than the smallest practical electrode spacing, this error is smaller than that inherent in a two-electrode system. Since voltage-gradients are automatically compensated, it is possible to obtain continuous readings of potential and current. A ‘voltage-clamp’ circuit is described, which allows the time-course of the short-circuit current to be studied. The three-electrode system has been used to study the larval midgut of Hyalophora cecropia. The average results from five experiments were: initial potential difference (open-circuit): 98 ± 11 mV (S.E.M.); short-circuit current at time 6omin: 498 ± 160μA cm−2; ‘steady-state’ resistance at 60 min: 150 ± 26 Ω. cm2. The current is equivalent to a net potassium transport of 18.6 μ-equiv cm−2 h−1. The electrical parameters of the midgut change rapidly with time. The potential difference decays with a half-time of about 158 min, the resistance increases with a half-time of about 16 min, and the short-circuit current decays as the sum of two exponential terms, with half-times of about 16 and 158 min respectively. In addition, potential and short-circuit current show transient responses to step changes. The properties of the midgut are compared with those of other transporting epithelia, and their dependence on the degree of folding of the preparation is discussed. Their time-dependence is discussed in the context of changes in potassium content of the tissue, and the implications for measurements depending on the assumption of a steady state are outlined. Note: Requests for reprints should be addressed either to Dr Moreton at Cambridge, or to Professor W. R. Harvey, Dept. of Biology, Temple University, Philadelphia, Pennsylvania 19122, U.S.A.

Sodium and chloride transport in the large intestine of potassium-loaded rats

1986 ◽  
Vol 251 (2) ◽  
pp. G249-G252 ◽  
Author(s):  
M. E. Budinger ◽  
E. S. Foster ◽  
J. P. Hayslett ◽  
H. J. Binder
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Sodium Absorption ◽  
Chloride Absorption ◽  
Dietary Potassium ◽  
Potassium Secretion ◽  
Potassium Loading

Increased dietary potassium ("potassium loading") induces several adaptive changes in colonic function, including increased potential-dependent potassium secretion, active potassium secretion, and Na-K-ATPase activity, but does not alter net sodium absorption in vivo. To establish whether potassium loading stimulates active sodium transport, unidirectional, net sodium, and chloride fluxes were determined under voltage-clamp conditions across isolated rat distal colonic mucosa. In normal animals net sodium flux (JNanet), net chloride flux (JClnet) and short-circuit current (Isc) were 6.1 +/- 1.1, 8.4 +/- 1.0, and 0.7 +/- 0.1 mu eq X h-1. cm-2, respectively; potassium loading significantly increased JNanet and Isc by 4.9 +/- 1.4 and 3.5 +/- 0.7 mu eq X h-1 X cm-2, respectively, without changing JClnet. Amiloride (0.1 mM) inhibited the increases in JNanet and Isc produced by potassium loading. In Cl-free Ringer solution in normal animals JNanet was reduced to 0.6 +/- 0.3 mu eq X h-1 X cm-2. Potassium loading produced identical increases in JNanet and Isc, which were also completely inhibited by 0.1 mM amiloride. These studies establish that potassium loading induces amiloride-sensitive electrogenic sodium absorption without affecting electroneutral sodium-chloride absorption.

Mechanism of active potassium absorption and secretion in the rat colon

1984 ◽  
Vol 246 (5) ◽  
pp. G611-G617 ◽  
Author(s):  
E. S. Foster ◽  
J. P. Hayslett ◽  
H. J. Binder
Keyword(s):  
Colonic Mucosa ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Proton Exchange ◽  
Secretory Process ◽  
Rat Colon ◽  
Potassium Flux ◽  
Potassium Absorption ◽  
Potassium Secretion

To characterize and contrast the active potassium absorptive and secretory processes present in the rat colon, unidirectional 42K fluxes were performed under short-circuit conditions across isolated distal (D) and proximal (P) colonic mucosa of control rats and animals with hyperaldosteronism due to sodium depletion (aldosterone group). In the control D colon there was net potassium absorption (+0.51 +/- 0.07 mueq X h-1 X cm-2). The absorptive process appears electroneutral because net potassium flux ( JK net ) was unchanged in sodium-free Ringer solution (+0.76 +/- 0.12 mueq X h-1 X cm-2), whereas short-circuit current (Isc) was reduced to zero, and in chloride-free Ringer solution. In P colon of controls, net potassium secretion was -0.19 +/- 0.02 mueq X h-1 X cm-2 and was abolished by removal of sodium but not by removal of chloride. In both P and D colon aldosterone produced active potassium secretion (-0.39 +/- 0.06 mueq X h-1 X cm-2, P less than 0.001, and -0.90 +/- 0.07 mueq X h-1 X cm-2, P less than 0.001, respectively) that was sodium and chloride dependent. Although mucosal amiloride in D colon of aldosterone animals reduced net sodium flux to zero and reversed Isc from 4.1 +/- 0.6 to -1.1 +/- 0.1 mueq X h-1 X cm-2, net potassium secretion was not affected. Thus, in the presence of amiloride, Isc is accounted for by JK net (-0.93 +/- 0.12 mueq X h-1 X cm-2). These data indicate that 1) the active potassium absorptive process is electroneutral and could be explained by a potassium-proton exchange, and 2) the potassium secretory process is stimulated by aldosterone, is not inhibited by amiloride, and probably is electrogenic.

Dietary potassium modulates active potassium absorption and secretion in rat distal colon

1986 ◽  
Vol 251 (5) ◽  
pp. G619-G626 ◽  
Author(s):  
E. S. Foster ◽  
G. I. Sandle ◽  
J. P. Hayslett ◽  
H. J. Binder
Keyword(s):  
Short Circuit ◽  
Distal Colon ◽  
Ringer Solution ◽  
Potassium Transport ◽  
Bathing Solution ◽  
Dietary Potassium ◽  
Rat Distal Colon ◽  
Potassium Absorption ◽  
Potassium Secretion ◽  
Potassium Loading

To determine the effect of variations in body stores of potassium on the rate of active potassium transport in the large intestine, unidirectional 42K fluxes were performed under short-circuit conditions across isolated distal colonic mucosa of control, dietary potassium-depleted and dietary potassium-loaded rats. Potassium depletion stimulated net potassium absorption (JK net) (0.87 +/- 0.19 vs. 0.49 +/- 0.04 mu eq X h-1 X cm-2, P less than 0.025) due to a 40% increase in mucosal-to-serosal potassium transport (JK m----s). In sodium-free Ringer solution JK net in the potassium-depleted group was also significantly greater than in controls (1.93 +/- 0.26 vs. 1.01 +/- 0.11 mu eq X h-1 X cm-2, P less than 0.005). In contrast, in chloride-free Ringer solution JK net was identical in the control and potassium-depleted groups (0.39 +/- 0.05 vs. 0.46 +/- 0.07 mu eq X h-1 X cm-2, P = NS). Potassium loading reversed net potassium absorption to net potassium secretion (-0.76 +/- 0.08 mu eq X h-1 X cm-2, P less than 0.001) as the result of a decrease in JK m----s and an increase in serosal-to-mucosal potassium transport (JK s----m). Net potassium secretion was abolished in the absence of either sodium or chloride from the bathing solution but not by mucosal amiloride. In sodium-free Ringer solution JK net was similar in control and potassium-loaded groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that aldosterone influences transport in target tissues by dissimilar mechanisms

1985 ◽  
Vol 248 (4) ◽  
pp. F507-F512 ◽  
Author(s):  
D. Hirsch ◽  
P. Pace ◽  
H. J. Binder ◽  
J. P. Hayslett
Keyword(s):  
Distal Colon ◽  
Proximal Colon ◽  
Potassium Transport ◽  
Potential Difference ◽  
Sodium Absorption ◽  
Potassium Secretion ◽  
Secondary Hyperaldosteronism ◽  
Induced Changes ◽  
Sodium And Potassium

The present study was performed to answer the question: Is the action of aldosterone on electrolyte transport and electrical properties similar in all target tissues? Studies were performed in vivo in control animals and rats with secondary hyperaldosteronism, caused by a sodium-free diet, to compare the effects of hyperaldosteronism on distal colon with hormone-induced changes in proximal colon. In distal colon aldosterone increased net sodium absorption and potassium secretion approximately threefold. Transmural potential difference increased from -15 +/- 2 to -83 +/- 3 mV (lumen negative) and ISC rose from 167 +/- 26 to 1,023 +/- 17 microA X cm-2. These aldosterone-induced responses were completely inhibited by 0.1 mM amiloride. In contrast, in proximal colon potential difference was unchanged or increased slightly in experimental animals and ISC increased only 28% above control, although increases in net sodium and potassium transport were similar to changes observed in distal colon. Amiloride did not reduce sodium absorption in proximal colon of animals with hyperaldosteronism; ISC was decreased by 43%. These studies demonstrate that rat proximal colon is an aldosterone-sensitive tissue, but that the mechanism by which aldosterone influences sodium transport is not identical in distal and proximal portions of colon.

Effect of acid lumen pH on potassium transport in renal cortical collecting tubules

1976 ◽  
Vol 230 (1) ◽  
pp. 239-244 ◽  
Author(s):  
JF Boudry ◽  
LC Stoner ◽  
MB Burg
Keyword(s):  
Mean Value ◽  
Potassium Transport ◽  
Sodium Absorption ◽  
Positive Voltage ◽  
Tubule Lumen ◽  
Potassium Secretion ◽  
Transepithelial Voltage ◽  
Renal Tubular ◽  
Collecting Tubules

In order to determine the effect of acid lumen pH on renal tubular potassium transport, cortical collecting tubules were dissected from rabbit kidneys and perfused in vitro. When the pH of the perfusate was lowered from 7.4 to 6.8, potassium secretion into the tubule lumen decreased by an average of 47%. The transepithelial voltage increased from a mean value of -32 mV (lumen negative) at pH 7.4 to -51 mV at PH 6.8. Net sodium absorption from the tubule lumen was essentially unchanged (5% mean decrease). Transepithelial voltage and potassium secretion returned to control values when the pH of the perfusate was raised to 7.4. Alterations in pH of the bath had no comparable effect on the transepithelial voltage, whether the bath pH was increased or decreased. We conclude that a decrease in the pH of the tubule fluid of itself inhibits active potassium secretion in this tubule segment, providing an additional explanation for the decrease in potassium excretion found in acidosis. The negative voltage (presumably caused by sodium absorption out of the lumen) is increased under these conditions, possibly because of reduction of a smaller counterbalancing positive voltage caused by potassium secretion into the lumen.

Comparison of Potassium Transport in Three Structurally Distinct Regions of The Insect Midgut

1981 ◽  
Vol 91 (1) ◽  
pp. 103-116
Author(s):  
MOIRA CIOFFI ◽  
WILLIAM R. HARVEY
Keyword(s):  
Goblet Cell ◽  
Apical Membrane ◽  
Close Association ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Structural Requirement ◽  
Posterior Midgut ◽  
New Information ◽  
Structural And Functional Properties

1. Active potassium transport across the isolated midgut of the Tobacco Hornworm larva, Manduca sexta, was studied by measuring the short circuit current (ISC) and unidirectional 42-potassium fluxes. 2. The midgut is composed of structurally distinct anterior, middle and posterior regions, all of which are shown to transport potassium, so that by comparing and contrasting their structural and functional properties new information on the mechanism of midgut potassium transport was obtained. 3. It has previously been shown that the potassium pump is located on the apical membrane of the goblet cell. In the anterior and middle regions of the midgut the goblet cell has a large cavity and mitochondria are closely associated with the apical membrane while in the posterior midgut the goblet cavity is much smaller, and mitochondria are not associated with the apical membrane. However, the apical membrane particles which have been implicated in active potassium transport in a number of other insect epithelia are present in all three regions. This observation suggests that the particles are a structural requirement for active transport, and that close association between mitochondria and the transporting membrane is not essential. 4. Comparison of the kinetic influx pool size and the differences in the ISC decay profiles between the three midgut regions suggest that part of the influx pool is a transported pool located in the goblet cavity. 5. A new model to explain the driving force for potassium transport in the midgut is proposed, in which the rate of potassium transport controls the entrance of potassium into the cell, rather than the opposite, currently accepted view.

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