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1.
Yuan-Heng Tai Jehan-F. Desjeux Giustina Danisi Peter F. Curran 《The Journal of membrane biology》1977,31(1):189-208
Summary Na and Cl fluxes and short-circuit current (I
sc) in rabbit ileum have been studied as a function of ionic concentrations in HCO3-free solutions. Both net Na flux (J
net
Na
) andI
sc show similar saturation functions of [Na] at fixed [Cl]. They show no significant difference between zero and 112mm Na but at 140mm NaI
sc is significantly greater than theJ
net
Na
. Net Cl transport, secretion, is observed only at 140mm Na and is approximately equivalent to the difference between theI
sc andJ
net
Na
. The transcellular mucosa-to-serosa Na fluxes measured at 140 and 70mm Na do not differ significantly from the correspondingI
sc. The net Cl flux varies with [Cl] at fixed [Na] whileI
sc is virtually not affected by [Cl]. These results suggest that the absorptive Na transport process is electrogenic and responsible for theI
sc and that the secretory fluxes of Na and Cl are coupled, require high [Na], vary with [Cl], and do not contribute toI
sc. K-free solution abolishes theI
sc after a prolonged lag. Finally, the effect of a low resistance shunt pathway on active Na absorption is examined with a four-compartment model.Deceased (October 16, 1974). 相似文献
2.
The involvement of second messengers in modulating Schistocerca gregaria rectal ion and fluid transport was investigated using two in vitro bioassay systems: everted rectal sacs and rectal flat sheets. Various agents known to block or activate specific signal transduction pathways were employed in these bioassays. Cyclic AMP stimulated rectal fluid reabsorption (Jv) and Cl− transport (Isc) to the same extent as aqueous extracts of corpus cardiacum storage lobes. Cyclic GMP also partially (50%) stimulated both rectal Jv and Isc. Exogenous Ca2+ was not required for the maintenance of rectal transport, indeed Ca2+ free conditions increased the amount of stimulatable Jv. There was some evidence indicating intracellular Ca2+ may play a minor role in controlling rectal transport. The phospholipase C mediated signal transduction pathway was not involved with the stimulation of rectal transport, and appeared to have an inhibitory role. Neuroparsins, antidiuretic neuropeptides from Locusta migratoria, showed no activity upon either S. gregaria rectal ion or fluid transport. The findings of this study show that the two closely related insects possess discrete antidiuretic factors which stimulate rectal transport via different signal transduction pathways. © 1996 Wiley-Liss, Inc. 相似文献
3.
R. Krattenmacher Rosita Voigt W. Clauss 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(2):161-165
Summary Transepithelial electrogenic Na transport (INa) was investigated in the colon of the frog Xenopus laevis with electrophysiological methods in vitro. The short circuit current (Isc) of the voltage-clamped tissue was 24.2±1.8 A·cm-2 (n=10). About 60% of this current was generated by electrogenic Na transport. Removal of Ca2+ from the mucosal Ringer solution stimulated INa by about 120%. INa was not blockable by amiloride (0.1 mmol·l-1), a specific Na-channel blocker in epithelia, but a fully and reversible inhibition was achieved by mucosal application of 1 mmol·l-1 lanthanum (La3-). No Na-self-inhibition was found, because INa increased linearly with the mucosal Na concentration. A stimulation of INa by antidiuretic hormones was not possible. The analysis of fluctuations in the short circuit current (noise analysis) indicated that Na ions pass the apical cell membrane via a Ca-sensitive ion channel. The results clearly demonstrate that in the colon of Xenopus laevis Na ions are absorbed through Ca-sensitive apical ion channels. They differ considerably in their properties and regulation from the amiloride-sensitive Na channel which is typically found in the colon of vertebrates.Abbreviations
G
T
transepithelial conductance
-
I
sc
short circuit current
-
I
Na
transepithelial Na-current
-
m
mucosal
-
s
serosal
-
PDS
power density spectrum
-
f
frequency
-
f
c
corner frequency of the Lorentzian component of the PDS
-
S(f)
power density of the Lorentzian component of the PDS
- So
plateau value of the Lorentzian component of the PDS 相似文献
4.
Summary Previously we have shown that the inhibition of active transport by amiloride is noncompetitive with sodium inRana catesbeiana skin, suggesting that amiloride acts at a site separate from the sodium entry site (Benos, D.J., Mandel, L.J., Balaban, R.S. 1979,J. Gen Physiol.
73: 307). In the present study, the effects of a number of sulfhydryl, amino, and carboxyl group selective reagents were studied on short-circuit current (I
sc) as well as the efficacy of amiloride in bullfrog skin, to determine those functional ligands which may be involved with either of these processes.Addition of the sulfhydryl reagent PCMBS (1mm) to the outside bathing medium produced biphasic effects, initially reversibly increasingI
sc by an average 56% followed by a slower, irreversible decay to levels below baseline. In contrast, the addition of 0.1mm PCMB always resulted in a rapid, irreversible decrease inI
sc. When a 40,000 mol wt dextran molecule was attached to PCMB, a stable, reversible increase inI
sc was observed. These observations suggest that at least two populations of-SH groups are involved in Na translocation through the entry step. Amiloride was equally effective in inhibitingI
sc before and after treatment with PCMBS both during the stimulatory as well as the inhibitory phase. The sulfhydryl reducing agent DTT, and oxidizing agent DTNB had only minor influence onI
sc
and did not alter the effectiveness of amiloride.Similarly, the amino reagents, SITS and TNBS did not affectI
sc. However, TNBS decreased the ability of amiloride to inhibit Na entry. These results suggest that an amino group may be involved in the interaction of amiloride and its site, without affecting Na entry.The carboxyl reagents EEDQ, TMO, and three separate carbodiimides were without effect onI
sc or amiloride inhibition. Methylene blue (MB), a molecule that interacts with both carboxyl and hydroxylspecific groups, inhibitedI
sc by 20% and decreased amiloride's ability to inhibitI
sc. These effects, however, are likely to occur from the cytoplasmic side as MB appears to enter into the cells.These results support the notion that amiloride and Na interact with the entry protein at different regions on the membrane. 相似文献
5.
Klaus Turnheim Raymond A. Frizzell Stanley G. Schultz 《The Journal of membrane biology》1978,39(2-3):233-256
Summary Ouabain abolishes the short-circuit current (I
sc
) and decreases the transepithelial conductance (G
t
) of rabbit colon. In contrast, amphotericin B elicits a maximumI
sc
and markedly increasesG
t
. However, inboth instances the amiloride-sensitive Na entry step is completely blocked, presumably due to an increase in cell Na. Conversely, when Na-depleted tissues are suddenly exposed to 140mm Na, the amiloride-sensitiveI
sc
and the amiloride-sensitive component ofG
t
(
a
G
Na
) increase abruptly to their maximum values and the decline to steady-state plateaus with a half time of 6 min; throughout the decline (I
sc/a
G
Na)=E
Na is constant at a value of 95 mV. In the presence of amphotericin B, theI
sc
abruptly rises to the same maximum but does not decline. These findings indicate that in the presence of 140mm Na the conductance of the amiloride-sensitive Na entry step can vary from a maximum value of approximately 1.6 mmhos/cm2 when cell Na is depleted, to zero when cell Na is abnormally elevated (e.g., in the presence of ouabain or amphotericin B). Our findings are consistent with a system in which the pathway responsible for transcellular Na transport parallels another cellular compartment with which it communicates. The Na capacity of the active transport pathway appears to be very small so that this compartment fills rapidly after exposure of Na-depleted cells to 140mm Na, and active transepithelial Na transport is initiated and reaches steady-state levels quickly. The Na capacity of the second compartment is much larger; the Na content of this compartment appears to be responsible for the negative feedback effect on the permeability of the amiloride-sensitive entry step. 相似文献
6.
Transport of sodium and potassium in intestinal epithelial cells 总被引:1,自引:0,他引:1
Richard C. Rose 《Life sciences》1976,18(11):1229-1236
Transport properties of rabbit small intestinal mucosa were investigated to characterize the process by which epithelial cells maintain normal Na and K gradients across the cell membrane. Active transport of Na from the cell proceeded at a faster rate in the presence of K; and active transport of K into the cell was stimulated by the presence of Na. Following preincubation at 0°C to reduce tissue K content, a greater transmural electrical potential difference (PD) and short-circuit current (Isc) developed as the temperature was raised to 37°C if K was present in the bathing solution. The PD and Isc, which generally reflect the rate of active Na transport in ileum under control conditions, increased immediately upon raising the K concentration in the serosal solution from 0 to 10 nM.The results present the first direct indication in mammalian intestine of an interdependence of the Na and K active transport processes which regulate the intracellular content of these cations. 相似文献
7.
Peter M. Spooner Isidore S. Edelman 《Biochimica et Biophysica Acta (BBA)/General Subjects》1976,444(3):663-673
The action of aldosterone on active Na+ transport was assessed under aerobic and anaerobic conditions in the isolated urinary bladder of the toad, BUfo marinus. Aldesterone augmented the short-circuit current (Isc) under rigorous anaerobiosis. Four lines of evidence indicate that the increase in anaerobic Isc does not represent an equivalent increase in active Na+ transport: 1. Net Na+ transport, determined by isotopic fluxes, was the same in the aldosterone-treated and control quarter-bladders, and significantly greater than the simultaneously measured Isc. 2. Amiloride, an inhibitor of the apiral entry of Na+, did not reduce the steroid-dependent increase in the anaerobic Isc. 3. Substitution of choline for Na+ in the mucosal medium reduced the magnitude of the anaerobic Isc values did not eliminate the effect of aldosterone. 4. Addition of ouabain, a potent inhibitor of the Na+ pump, partially inhibited the effect of aldosterone on the anerobic Isc but a significant hormonal increment remained. The source of the anaerobic Isc was not identified; an effort was made, however, to determine the dependence of this current on glycolysis. During anaerobics, aldosterone increased the integral Isc by 42% but did not alter lactate production. These results suggest that the steroid-dependent increase in the anaerobic Isc may involve effects on permeability properties of the epithelium rather than on active tranport systems. 相似文献
8.
Ion Transport in Isolated Rabbit Ileum : II. The interaction between active sodium and active sugar transport 总被引:19,自引:2,他引:17
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The addition of actively transported sugars to the solution bathing the mucosal surface of an in vitro preparation of distal rabbit ileum results in a rapid increase in the transmural potential difference, the short-circuit current, and the rate of active Na transport from mucosa to serosa. These effects are dependent upon the active transport of the sugar per se and are independent of the metabolic fate of the transported sugar. Furthermore, they are inhibited both by low concentrations of phlorizin in the mucosal solution and by low concentrations of ouabain in the serosal solution. The increase in the short-circuit current, ΔIsc, requires the presence of Na in the perfusion medium and its magnitude is a linear function of the Na concentration. On the other hand, ΔIsc is a saturable function of the mucosal sugar concentration which is consistent with Michaelis-Menten kinetics suggesting that the increase in active Na transport is stoichiometrically related to the rate of active sugar transport. An interpretation of these findings in terms of a hypothetical model for intestinal Na and sugar transport is presented. 相似文献
9.
Anthony Samson Kirk L. Hamilton A. Grant Butt 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2000,125(4)
In this study, we have used the mouse intestine and the Ussing short circuit technique to compare the effects and mechanism of action of somatostatin (SST, 0.1 μM) on cAMP- and Ca2+-mediated ion secretion in the duodenum and colon of the Swiss-Webster mouse. The cAMP-dependent secretagogues, prostaglandin E2 (1 μM) and dibutyryl-cAMP (150 μM) increased short circuit current (Isc) in both regions, but only the colonic response was inhibited by SST. This inhibition was independent of enteric nerves, suggesting a direct action on the epithelial cells. The Ca2+-dependent secretagogue carbachol (10 μM) stimulated a transient increase in Isc in both intestinal segments. In the duodenum, SST partially inhibited this increase in Isc and both the responses to carbachol and SST were independent of enteric nerves. In the colon, while SST inhibited the carbachol induced increase in Isc, pre-treatment with tetrodotoxin (750 nM) profoundly inhibited the carbachol induced increase in Isc, thus markedly reducing the inhibitory effect of SST. This indicates an involvement of the enteric nervous system in the response to carbachol and the action of SST in the colon. These data indicate marked regional differences within the mouse intestine of the effects of SST on ion secretion and demonstrate different mechanisms of action of SST in the duodenum and colon. 相似文献
10.
Summary The unidirectional influx of Na from the mucosal solution into the epithelium ofin vitro descending rabbit colon (J
me
Na
) determined under short-circuit conditions, is comprised of two components: one represents entry of Na into transporting epithelial cells and is abolished by amiloride which also abolishes Na absorption (J
net
Na
). The other represents diffusional Na entry into paracellular pathways traversing the epithelium. In all instances, exposure of the mucosal surface to amphotericin B increased tissue conductance andJ
me
Na
and elicited K secretion. Tissues showing a spontaneousI
sc of approximately 4 eq/cm2hr did not respond to amphotericin B with increasedI
sc andJ
net
Na
. However, in tissues characterized by a lowerI
sc under control conditions, amphotericin B increasedI
sc andJ
net
Na
to approximately 4eq/cm2hr. These findings suggest that amphotericin increasesJ
net
Na
and elicits K secretion by disrupting the normal permselectivity of the mucosal membrane. Under these conditions the extrusion of Na from cell-to-serosal solution becomes the rate limiting step in transepithelial Na transport. Finally, a close correlation betweenJ
me
Na
andJ
net
Na
was observed when the rate of Na absorption varied either spontaneously or experimentally with amiloride, suggesting that the backflux of Na from cell-to-mucosal solution is undetectably small. 相似文献
11.
Summary The renal cell line LLC-PK1 cultured on a membrane filter forms a functional epithelial tissue. This homogeneous cell population exhibits rheogenic Na-dependentd-glucose coupled transport. The short-circuit current (I
sc) was acccounted for by net apical-to-basolaterald-glucose coupled Na flux, which was 0.53±0.09(8) eq cm–2hr–1, andI
sc, 0.50±0.50(8) eq cm–2hr–1. A linear plot of concurrent net Na vs. netd-glucose apical-to-basolateral fluxes gave a regression coefficient of 2.08. As support for a 21 transepithelial stoichiometry, sodium was added in the presence ofd-glucose and the response ofI
sc analyzed by a Hill plot. A slope of 2.08±0.06(5) was obtained confirming a requirement of 2 Na for 1d-glucose coupled transport. A Hill plot ofI
sc increase to addedd-glucose in the presence of Na gave a slope of 1.02±0.02(5). A direct determination of the initial rates of Na andd-glucose translocation across the apical membrane using phlorizin, a nontransported glycoside competitive inhibitor to identify the specific coupled uptake, gave a stoichiometry of 2.2 A coupling ratio of 2 for Na,d-glucose uptake, doubles the potential energy available for Na-gradient coupledd-glucose transport. In contrast to coupled uptake, the stoichiometry for Na-dependentphlorizin binding was 1.1±0.1(8) from Hill plot analyses of Na-dependent-phlorizin binding as a function of [Na]. Although occurring at the same site the process of Na-dependent binding of phlorizin differs from the binding and translocation ofd-glucose. Our results support a two-step, two-sodium model for Na-dependentd-glucose cotransport; the initial binding to the cotransporter requires a single Na andd-glucose, a second Na then binds to the ternary complex resulting in translocation. 相似文献
12.
J. Pácha 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(6):495-498
To evaluate the developmental changes in colonic Na+ transport, Na, K-ATPase activity and the sensitivity of the short-circuit current to amiloride were investigated. The amiloride-sensitive short-circuit current which represents the electrogenic, amiloride-sensitive Na+ transport through Na+ channels, was not present in chicken embryos but rose significantly after hatching in chicks which were kept on a low-salt diet. Amiloride-sensitive short-circuit current increased gradually but the plateau was not reached during the first 15 days of life. Drinking of 0.9% NaCl totally inhibited the induction of amiloride-sensitive Na+ transport. Na+, K+-ATPase activity increased during development but was not influenced by changes in salt intake. Na+ transport in chicken colon therefore undergoes profound developmental changes. The increase of Na+ transport refleets not only the adaptation of colonocytes to low salt intake but also the maturation of Na+ absorption in colon. The possible role of aldosterone in the adaptation to low-salt intake is discussed.Abbreviations LS
low-salt
- HS
high-salt
-
I
sc
short-circuit current 相似文献
13.
Summary Segments of descending colon obtained from rabbits, that had been maintained on drinking water containing 25mm NaCl and an artificial diet which contains 1% Na and is nominally K-free, respond to aldosterone in vitro (after a 30 to 60-min lag period) with a marked increase in the short-circuit current (I
sc
), an equivalent increase in the rate of active Na absorption (J
net
Na
) and a decline in tissue resistance (R
t
). Aldosterone also brings about a marked increase in the unidirectional influx of Na into the cells across the mucosal membrane (zero-time rate of uptake) which does not differ significantly from the increase inI
sc
. Treatment of control tissues with amphotericin B brings about sustained increases inI
sc
andJ
net
Na
to levels observed in aldosterone-treated tissues. However, addition of amphotericin B to the mucosal solution of aldosteronetreated tissues does not result in a sustained increase inI
sc
orJ
net
Na
and these values do not differ markedly from those observed in control tissues treated with amphotericin B. These findings, together with other evidence that Na entry in the presence of amphotericin B is sufficiently rapid to saturate the active Na extrusion mechanism at the baso-lateral membrane, are consistent with the notion that the aldosterone-induced protein increases the permeability of the mucosal membrane to Na but does not increase the saturation level of the active Na pump within the time-frame of these studies (3 hr).Finally, aldosterone has no effect on the bidirectional or net transepithelial movements of K under short-circuit conditions, suggesting that the enhanced secretion of K observed in vivo is the result of increased diffusion of K from plasma to lumen via paracellular pathways in response to an increased transepithelial electrical potential difference (lumen negative). 相似文献
14.
V. Casavola L. Guerra S.J. Reshkin K.A. Jacobson F. Verrey H. Murer 《The Journal of membrane biology》1996,151(3):237-245
The effect of adenosine regulation on sodium and chloride transport was examined in cultured A6 renal epithelial cells. Adenosine and its analogue N6-cyclopentyladenosine (CPA) had different effects on short-circuit current (I
sc) depending on the side of addition. Basolateral CPA addition induced an approximately threefold increase of the I
sc that reached a maximum effect 20 min after addition and was completely inhibited by preincubation with either an A2 selective antagonist, CSC, or the sodium channel blocker, amiloride. Apical CPA addition induced a biphasic I
sc response characterized by a rapid fourfold transient increase over its baseline followed by a decline and a plateau phase
that were amiloride insensitive. The A1 adenosine antagonist, CPX, completely prevented this response. This I
sc response to apical CPA was also strongly reduced in Cl−-free media and was significantly inhibited either by basolateral bumetanide or apical DPC preincubation. Only basolateral
CPA addition was able to induce an increase in cAMP level. CPA, added to cells in suspension, caused a rapid rise in [Ca2+]
i
that was antagonized by CPX, not affected by CSC and prevented by thapsigargin preincubation. These data suggest that basolateral
CPA regulates active sodium transport via A2 adenosine receptors stimulating adenylate cyclase while apical CPA regulates Cl− secretion via A1 receptor-mediated changes in [Ca2+]
i
. 相似文献
15.
Timothy R. Traynor Scott M. O'Grady 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(1):47-53
Summary Porcine distal colon epithelium was mounted in Ussing chambers and bathed in plasma-like Ringer solution. Tissue conductances ranged from 10 to 15 mS and the short-circuit current (Isc) ranged from-15 to 220 A·cm-2. Variations in basal Isc resulted from differences in the amount of amiloride (10M mucosal addition)-sensitive Na+ absorption. Ion substitution and transepithelial flux experiments showed that 10 M amiloride produced a decrease in the mucosal-to-serosal (M-S) and net Na flux, and that this effect on Isc was independent of Cl- and HCO
3
-
replacement. When the concentration of mucosal amiloride was increased from 10 to 100 M, little change in Isc was observed. However, increasing the concentration to 1 mM produced a further inhibition, which often reversed the polarity of the Isc. The decrease in Isc due to 1 mM amiloride was dependent on both Cl- and HCO
3
-
, and was attributed to reductions in the M-S and net Na+ fluxes as well as the M-S unidirectional Cl- flux. Ion replacement experiments demonstrated that Cl- substitution reduced the M-S and net Na fluxes, while replacement of HCO
3
-
with HEPES abolished net Cl- absorption by reducing the M-S unidirectional Cl- flux. From these data it can be concluded that: (1) Na+ absorption is mediated by two distinct amiloride-sensitive transport pathways, and (2) Cl- absorption is completely HCO
3
-
-dependent (presumably mediated by Cl-/HCO
3
-
exchange) and occurs independently of Na+ absorption.Abbreviations Gt
tissue conductance
- HEPES
tris (hydroxymethyl) aminomethane
- (tris)
N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid
- Isc
short-circuit current
- Jr
residual flux
- M-S
mucosal-to-scrosal
- S-M
serosal-to-mucosal
- TTX
tetrodotoxin 相似文献
16.
The effect of conjugated dihydroxy and trihydroxy bile salts on electrolyte transport across isolated rabbit jejunal mucosa was studied. Both taurochenodeoxycholic acid and taurocholic acid increased the short-circuit current (Isc) in bicarbonate-Ringer solution but not in a bicarbonate-free, chloride-free solution. Taurochenodeoxycholic acid was significantly more effective than taurocholic acid in increasing Isc. The presence of theophylline prevented the taurochenodeoxycholic acid-and taurocholic acid-induced increase in Isc. Transmural ion fluxes across jejunal mucosa demonstrated that 2 mM taurochenodeoxycholic acid decreased net Na+ absorption, increased net Cl− secretion and increased the residual flux (which probably represents HCO3− secretion). These studies support the hypothesis that cyclic AMP may be a mediator of intestinal electrolyte secretion. 相似文献
17.
John Gutknecht 《The Journal of general physiology》1967,50(7):1821-1834
Ion transport in the giant celled marine alga, Valonia ventricosa, was studied during internal perfusion and short-circuiting of the vacuole potential. The perfusing and bathing solutions were similar to natural Valonia sap and contained the following concentrations of major ions: Na 51, K 618, and Cl 652 mM. The average short-circuit current (I
sc) was 97 pEq/cm2 sec (inward positive current), and the average open-circuit potential difference (PD) was 74 mv (vacuole positive to external solution). Perfused and short-circuited cells showed a small net influx of Na (2.0 pEq/cm2 sec) and large net influxes of K (80 pEq/cm2 sec) and Cl (50 pEq/cm2 sec). Unidirectional K influx was proportional to I
sc, but more than one-half of the I
sc remained unaccounted for. Both the I
sc and PD were partly light-dependent, declining rapidly during the first 1–2 min of darkness. Ouabain (5 x 10-4
M) had little effect on the influx of Na or K and had no effect on I
inf or PD. Fluid was absorbed at a rate of about 93 pliter/cm2 sec. Reversing the direction of fluid movement by adding mannitol to the outside solution had little effect on ion movements. The ionic and electrical properties of normal and perfused cells of Valonia are compared. 相似文献
18.
Summary By in vitro experiments on rabbit bladder, we reassessed the traditional view that mammalian urinary bladder lacks ion transport mechanisms. Since the ratio of actual-to-nominal membrane area in folded epithelia is variable and hard to estimate, we normalized membrane properties to apical membrane capacitance rather than to nominal area (probably 1 F 1 cm2 actual area). A new mounting technique that virtually eliminates edge damage yielded resistances up to 78,000 F for rabbit bladder, and resistances for amphibian skin and bladder much higher than those usually reported. This technique made it possible to observe a transport-related conductance pathway, and a close correlation between transepithelial conductance (G) and short-circuit current (I
sc) in these tight epithelia.G andI
sc were increased by mucosal (Na+) [I
sc0 when (Na+)0], aldosterone, serosal (HCO
3
–
) and high mucosal (H+); were decreased by amiloride, mucosal (Ca++), ouabain, metabolic inhibitors and serosal (H+); and were unaffected by (Cl–) and little affected by antidiuretic hormone (ADH). Physiological variation in the rabbits' dietary Na+ intake caused variations in bladderG andI
sc similar to those caused by the expectedin vivo changes in aldosterone levels. The relation betweenG andI
sc was the same whether defined by diet changes, natural variation among individual rabbits, or most of the above agents. A method was developed for separately resolving conductances of junctions, basolateral cell membrane, and apical cell membrane from thisG–I
sc relation. Net Na+ flux equalledI
sc. Net Cl– flux was zero on short circuit and equalled only 25% of net Na+ flux in open circuit. Bladder membrane fragments contained a Na+–K+-activated, ouabain-inhibited ATPase. The physiological significance of Na+ absorption against steep gradients in rabbit bladder may be to maintain kidney-generated ion gradients during bladder storage of urine, especially when the animal is Na+-depleted. 相似文献
19.
《生物化学与生物物理学报:生物膜》1986,858(1):145-152
The transport characteristics of the skin of neotenic Ambystoma tigrinum were investigated using ion substitution and circuit analysis. When bathed with sodium Ringer solution on both sides, a transepithelial potential of up to 50 mV (inside positive) and a short-circuit current (Isc) of up to 10 μA/cm2 were observed. When amiloride was added or Na+ was replaced by tetramethylammonium in the apical solution, Isc was decreased from 3.7 ± 0.4 to 1.5 ± 0.2 μA/cm2 (n = 10). When K+ replaced Na+, there was a smaller change in Isc from 5.8 ± 0.6 to 3.7 ± 0.5 μA/cm2 (n = 10). Although barium had no effect when added to 100 K Ringer on normal skin, it inhibited Isc on skins taken from K+-loaded animals. Nystatin caused substantial increases in Isc with either Na+ or K+ as the dominant cation in the apical solution. Current voltage analysis using amiloride was used to estimate the resistances and electromotive forces (EMF) associated with ion transport. The EMF for ion transport was partially dependent on K+ in the basolateral solution and it was similar to that observed in other epithelia. The resistance of the transport pathway was high, consistent with the low Isc. These results suggest that there is an amiloride-sensitive Na+ channel in parallel with a small K+ conductance in the apical membrane of this preparation. 相似文献
20.
Summary Na, K-ATPase function was studied in order to evaluate the mechanism of increased colonic Na+ transport during early postnatal development. The maximum Na+-pumping activity that was represented by the equivalent short-circuit current after addition of nystatin (I
sc
N
) did not change during postnatal life or after adrenalectomy performed in 16-day-old rats.I
sc
N
was entirely inhibited by ouabain; the inhibitory constant was 0.1mm in 10-day-old (young) and 0.4mm in 90-day-old (adult) rats. The affinity of the Na, K pump for Na+ was higher in young (11mm) than in adult animals (19mm). The Na, K-ATPase activity (measured after unmasking of latent activity by treatment with sodium dodecylsulfate) increased during development and was also not influenced by adrenalectomy of 16-day-old rats. The inhibitory constant for ouabain (K
I
) was not changed during development (0.1–0.3mm). Specific [3H]ouabain binding to isolated colonocytes increased during development (19 and 82 pmol/mg protein), the dissociation constant (K
D
) was 8 and 21 m in young and adult rats, respectively. The Na+ turnover rate per single Na, K pump, which was calculated fromI
sc
N
and estimated density of binding sites per cm2 of tissue was 500 in adult and 6400 Na+/min·site in young rats. These data indicate that the very high Na+ transport during early postnatal life reflects an elevated turnover rate and increased affinity for Na+ of a single isoform of the Na, K pump. The development of Na+ extrusion across the basolateral membrane is not directly regulated by corticosteroids. 相似文献