共查询到20条相似文献,搜索用时 31 毫秒
1.
G A Gerencser 《Biochimica et biophysica acta》1984,775(3):389-394
This investigation was principally undertaken to examine the mechanism of active chloride absorption across the Aplysia californica intestine by using various inhibitors of ion transport. Isolated intestine, mounted between identical oxygenated sodium-free seawater solutions, maintained stable transmural potential differences (serosa negative) and short-circuit currents for several hours at 25 degrees C. The metabolic inhibitors, 2,4-dinitrophenol and fluoride, reduced both transmural potential difference and short-circuit current; however, the electrical characteristics were predominantly dependent upon glycolytic energy. The addition of thiocyanate to the mucosal solution inhibited both electrical characteristics in parallel, and this inhibition could be titrated according to the thiocyanate concentration. The short-circuit current was carried wholly by a net active chloride transfer from mucosa to serosa as determined by flux measurements. These results suggest that active chloride absorption may be mediated by a primary active transport process. 相似文献
2.
Summary When bathed on both sides with identical chloride-containing salines thein vitro preparation of the plaice intestine maintains a negative (serosa to mucosa) short-circuit current of 107±11 A/cm2, a transepithelial potential difference of 5.5±0.6 mV (serosa negative), and a mean mucosal membrane potential of –45.4±0.6 mV. Under these conditions the intracellular chloride activity is 32mm.If chloride in the bathing media is partially, or completely substituted by thiocyanate the measured electrical parameters do not change but transepithelial flux determinations show a reduction in chloride fluxes and the presence of a significant thiocyanate flux. The addition of piretanide (10–4
m) reduced the short-circuit current and the mucosa-to-serosa fluxes of chloride and thiocyanate; this inhibition is similar to the effect of piretanide on chloride transport in this tissue.The results indicate that thiocyanate is transported in this tissue via the piretanide-sensitive chloride pathway and are compared with the effects of thiocyanate on other tissues reported in the literature. 相似文献
3.
《Comparative biochemistry and physiology. A, Comparative physiology》1978,59(2):203-208
- 1.1. Addition of d-glucose, d-galactose, or d-3-o-methyl glucose to the mucosal bathing medium stimulated rapid sustained increases in transmural potential difference (serosa negative) and short-circuit current.
- 2.2. The change in short-circuit current increased curvilinearly with increasing concentrations of mucosal d-glucose.
- 3.3. Addition of phlorizin to the mucosal bathing medium partially inhibited the d-glucose stimulation of transmural potential difference and short-circuit current.
- 4.4. The major portion of the sugar-induced short-circuit current is carried by a net active chloride transfer from mucosa to serosa while the minor portion of the short-circuit current is wholly or predominantly carried by a net active sodium transfer from mucosa to serosa.
4.
P Badia T Gómez M Díaz A Lorenzo 《Comparative biochemistry and physiology. A, Comparative physiology》1987,87(4):883-887
1. Ionic fluxes of sodium and chloride across lizard colon mucosa were measured and compared with the electrical characteristics of the tissue under voltage-clamped conditions. 2. In a Ringer-bicarbonate solution there was both a net sodium flux (JNanet) and a net chloride flux (JClnet) from mucosa to serosa. The net flux residual (JR) was near zero, indicating that net sodium and chloride transport is the result of an electrically neutral transport mechanism. 3. In the presence of sodium, the net chloride flux was abolished and the short-circuit current (Isc) and the electrical potential difference (PD) were unchanged. In the absence of chloride the net sodium flux was abolished and the short-circuit current and electrical potential difference were not modified. 4. From an analysis of the effects of the inhibitors, furosemide, amiloride and disulfonic stilbene (DIDS), a plausible model was developed to explain the characteristics of sodium and chloride absorption. 相似文献
5.
《Comparative biochemistry and physiology. A, Comparative physiology》1978,59(2):209-212
- 1.1. Transmural potential difference and short-circuit current of intestinal sheets of Aplysia califonica were stable up to 5 hr.
- 2.2. Transmural potential difference was serosa negative relative to the mucosa and the short-circuit current was consistent with a net active anion transport from mucosa to serosa.
- 3.3. Transmural potential difference and short-circuit current were dependent upon the presence of sodium and chloride in the bathing medium.
- 4.4. Transmural potential difference and short-circuit current were predominantly dependent upon aerobic metabolism, however a finite residual electrical component was dependent upon glycolytic energy.
- 5.5. The major portion of the short-circuit current is carried by a net active chloride transfer from the mucosal to serosal compartments while the minor portion is carried by a net active sodium transfer in the same direction.
6.
Addition of 446 micron prostaglandin E1 (PGE1) to the serosal medium of isolated short-circuited bullfrog small intestine elicited small increases transmural potential difference and short-circuit current while addition of PGE1 to the mucosal medium caused no change in the electrical parameters. Addition of 100 micron indomethacin to the mucosal medium inhibited both potential difference and short-circuit current with a resultant increase in steady-state tissue resistance. In the presence of mucosal 100 micron indomethacin, serosal 60 micron PGE1 markedly stimulated transmural potential difference and short-circuit current with a resultant decrease in steady-state tissue resistance. Serosal arachidonic acid (330 micron) stimulated transmural potential difference and short-circuit current and this effect was abolished by the addition of 100 micron indomethacin to the mucosal medium. Serosal 60 micron PGE1 only stimulated the M (mucosa) leads to S (serosa) unidirectional flux of sodium. These results strongly suggest that the PGE1 action is mediated either via a series of metabolic reactions which possibly increase the permeability of the mucosal membrane to sodium or via direct stimulation of rheogenic sodium pump activity. 相似文献
7.
Addition of 446 μM prostaglandin E1 (PGE1) to the serosal medium of isolated short-circuited bullfrog small intestine elicited small increases in transmural potential difference and short-circuit current while addition of PGE1 to the mucosal medium caused no change in the electrical parameters. Addition of 100 μM indomethacin to the mucosal medium inhibited both potential difference and short-circuit current with a resultant increase in steady-state tissue resistance. In the presence of mucosal 100 μM indomethacin, serosal 60 μM PGE1 markedly stimulated transmural potential difference and short-circuit current with a resultant decrease in steady-state tissue resistance. Serosal arachidonic acid (330μM) stimulated transmural potential difference and short-circuit current and this effect was abolished by the addition of 100 μM indomethacin to the mucosal medium. Serosal 60 μM PGE1 only stimulated the M (mucosa) → S (serosa) unidirectional flux of sodium. These results strongly suggest that the PGE1 action is mediated either via a series of metabolic reactions which possibly increase the permeability of the mucosal membrane to sodium or via direct stimulation of rheogenic sodium pump activity. 相似文献
8.
F. Trischitta M. G. Denaro C. Faggio 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(6):370-376
The effects of acetylcholine analogues, serotonin and catecholamines on ion transport were studied in both the middle and
the posterior intestine of Anguilla anguilla, mounted in an Ussing chamber, with the aim of understanding whether these regulators affect different mechanisms in the
different tracts. In the middle intestine, acetylcholine analogues and serotonin decreased the serosa negative transepithelial
potential and short-circuit current without altering the transepithelial resistance; catecholamines reversed the inhibitory
effects of both regulators. Similar opposite effects were produced by both the acetylcholine analogues and noradrenalin in
the posterior intestine. However, the lowering of the short-circuit current elicited by serotonin was paralleled by the decrease
of the transepithelial resistance, whilst noradrenalin had the opposite effects on both parameters. These observations, together
with the results of experiments performed by measuring the dilution potential in the control condition and in the presence
of either serotonin or serotonin plus noradrenalin, led us to hypothesize that serotonin increases the anion conductance of
the paracellular pathway while noradrenalin decreases it. In both the middle and posterior intestine, these regulators probably
affect transcellular transport mechanisms by acting on the Na-K-Cl transporter; both acetycholine and serotonin decrease its
activity while noradrenalin increases it.
Accepted: 22 May 1999 相似文献
9.
David C. Dawson 《The Journal of membrane biology》1977,37(1):213-233
Summary Transmural fluxes of3H-mannitol and22Na or36Cl were measured simultaneously in portions of isolated turtle colon stripped of serosal musculature. The relationships between mannitol flux and the flux of Na or Cl are characteristic of simple diffusion and suggest that transmural mannitol flow is largely confined to a paracellular pathway where Na, Cl and mannitol move much as in free solution. The contribution of edge damage to the transmural mannitol flow appears to be minimal. Mucosal hyperosmolarity causes blisters in epithelial tight junctions and increases the diffusional permeability to Na and mannitol, suggesting that the rate-limiting barrier in the shunt path is the tight junction. If the total mucosa to serosa flux of Na is corrected for the portion traversing the shunt pathway it is apparent that changes in the short-circuit current are completely accounted for by the mucosa to serosal movement of Na through a cellular path. In addition, the serosa to mucosa flux of Na appears to be restricted to the shunt. These observations suggest that there is no appreciable backflux of Na through the active, cellular path. In the presence of 10–4
m amiloride the short-circuit current is markedly reduced and the mucosa to serosa Na flux is restricted to the shunt, so that the net Na flux is abolished. The small amiloride-insensitive short-circuit current is consistent with HCO3 secretion. Mucosa to serosa and serosa to mucosa fluxes of Cl appear to be largely restricted to the paracellular shunt path and there is no evidence for any net flow of Cl under short-circuit conditions. The total tissue conductance can be described as the sum of three components: a shunt conductance which is linearly related to the transmural mannitol flow, an active conductance which is linearly related to the short-circuit current and a small residual conductance. The shunt conductance is attributable to the diffusive movements of Na and Cl through the paracellular path. Variations in the active Na transport from tissue to tissue are largely attributable to variations in the apparent conductance of the active Na transport path. The driving force for active Na transport can be described as an apparent emf of approximately 130 mV. These results suggest that transmural mannitol flux provides a quantitative estimate of the ion permeability and electrical conductance of a paracellular shunt path across the isolated turtle colon and thereby facilitates the study of the transport characteristics and electrical properties of cellular paths for transepithelial solute movement. 相似文献
10.
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
11.
Ion Transport in Isolated Rabbit Ileum : I. Short-circuit current and Na fluxes 总被引:31,自引:17,他引:14
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The transmural potential difference, short-circuit current, and Na fluxes have been investigated in an in vitro preparation of isolated rabbit ileum. When the tissue is perfused with a physiological buffer, the serosal surface is electrically positive with respect to the mucosal surface and the initial potential difference in the presence of glucose averages 9 mv. Unidirectional and net Na fluxes have been determined under a variety of conditions, and in each instance, most if not all of the simultaneously measured short-circuit current could be attributed to the active transport of Na from mucosa to serosa. Active Na transport is dependent upon the presence of intact aerobic metabolic pathways and is inhibited by low concentrations of ouabain in the serosal medium. A method is described for determining whether a unidirectional ionic flux is the result of passive diffusion alone, in the presence of active transport of that ion in the opposite direction. Using this method we have demonstrated that the serosa-to-mucosa flux of Na may be attributed to passive diffusion with no evidence for the presence of carrier-mediated exchange diffusion or the influence of solvent-drag. 相似文献
12.
The unidirectional fluxes of sodium, chloride, and of the bicarbonate and CO(2) pair were determined across the isolated large intestine of the bullfrog, Rana catesbiana. The isolated large intestine of the frog is characterized by a mean transmembrane potential of 45 mv., serosal surface positive with respect to mucosal. The unidirectional sodium flux from mucosal to serosal surface was found to be equal to the short-circuit current, thus the net flux was less than the simultaneous short-circuit current. This discrepancy between active sodium transport and short-circuit current can be attributed to the active transport of cation in the same direction as sodium and/or the active transport of anion in the opposite direction. The unidirectional fluxes of chloride and the bicarbonate and CO(2) pair revealed no evidence for active transport of either anion. A quantitative study of chloride fluxes at 45 mv. revealed a flux ratio of 1.8 which is considerably less than a ratio of 6 expected for free passive diffusion. It was concluded that a considerable proportion of the isotopic transfer of chloride could be attributed to "exchange diffusion." Study of the electrical properties of the isolated frog colon reveals that it can be treated as a simple D. C. resistance over the range of -20 to +95 mv. 相似文献
13.
Gerhard Ehrenspeck 《生物化学与生物物理学报:生物膜》1982,684(2):219-227
Ouabain-treated turtle bladders bathed on both surfaces by identical HCO3?/CO2-containing, Cl?-free Na+ media exhibit a short-circuit current (Isc) and transepithelial potential (p.d.) serosa electronegative to mucosa. Addition of 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of cyclic nucleotide phosphodiesterase, rapidly reverses the direction of the Isc and p.d.. The IBMX-induced reversal of Isc and p.d. is (1) dependent on the presence of HCO3? (and CO2) in the serosal bathing fluid, (2) independent of Na+ and other ions in the bathing medium, (3) decreased by inhibitors of carbonic anhydrase or oxidative metabolism, (4) increased by the serosal addition of cyclic AMP or the disulfonic stilbene, SITS. The results constitute evidence that the reversed Isc elicited by IBMX represents electrogenic secretion of HCO3?. 相似文献
14.
Rectum transmural potential (PD) and short-circuit current (Isc) of the desert locust, Schistocerca gregaria, have been studied in vitro, with everted rectal wall preparations in solutions of different ionic composition. Initially, a PD of about 35 mV (lumen positive) and a Isc of about 300 μA cm?2 were recorded. Omission of sodium or potassium (Tris as substitute), from the luminal side or from both sides led to an increase of 4 to 6 mV in PD (lumen more positive) together with an increase in Isc. In the absence of chloride alone (sulphate as substitute) the PD quickly dropped to nearly zero. In each case the control values were recovered on replacing the corresponding ions. Neither the PD nor the Isc changed when substitutions affected only the haemocoelic solution. These findings corroborate the assumption that active transport of chloride ions from lumen to haemolymph is the major factor for transmural PD and account for the short-circuit current in the rectal wall of desert locust. A working scheme is given to explain the influence of sodium, potassium, and chloride ions on the PD. 相似文献
15.
Summary The relationships among ion current, membrane potential difference, and resistance of an epithelium are studied. The short-circuit technique introduced by Ussing and Zerahn does not completely short circuit the epithelium if the series resistance parallel to the cell layer between the voltage electrodes is not properly compensated. The residual potential difference across the epithelial cell layer in the short-circuit state is proportional to both the measured short-circuit current and the resistance of the diffusion barriers not compensated. In the conventionally short-circuited small intestinal mucosa the villus and crypt areas are hypo-polarized to different degrees rather than simultaneously hyper- and hypo-polarized. Short-circuiting the whole tissue reduces but does not abolish the passive net ion movement across the tissue. Measurements of the electrical properties of the whole and denuded rat distal small intestine in HCO3-Ringer solution containing 10mm glucose reveal that the measured short-circuit current has under-estimated approximately 33% of the true short-circuit current and that the passive net Na flux from serosa to mucosa and Cl flux from mucosa to serosa are not negligible in the short-circuit state. 相似文献
16.
Simultaneous measurements of the transmural potential difference (PD) and the short-circuit current intensity (Isc) in the posterior intestine of the fish Blennius parvicornis were made in normal Ringer and in solutions of different ionic composition. The ouabain effects on these two parameters were also tested in normal Ringer solution. The absence of K+ from the Ringer solution on both the mucosal and serosal sides has no apparent effect on the PD and Isc within the first 15 min, but it makes them null after 30 min. When Na+ is substituted in both compartments, using Tris as substitute, a serosal negativity increase is initially observed, but it gradually decreases to zero after 30 min of experimentation. Similarly the PD and Isc drop to zero in the absence of Cl- (sulfate as substitute). Ouabain diminishes the serosa negative potential difference to zero after 30 min presenting a lineal relation to the Isc. A likely transport mechanism for Cl- dependent on the Na+ - K+ pump, is discussed. 相似文献
17.
John F. White 《生物化学与生物物理学报:生物膜》1977,467(1):91-102
Isolated segments of Amphiuma small intestine bathed in chloride or sulfate buffer generate a greater short-circuit current and a larger change in current in response to galactose when the serosal muscle layers are stripped from the mucosa. Intact (unstripped) segments are not apparently anoxic since stripped segments exposed to serosal N2 for 3 h display normal short-circuit currents but a reduced potential response to galactose, while the presence of muscle layers tends to reduce the short-circuit current but does not alter the potential response to galactose. Bullfrog small intestine also generates greater short-circuit current following removal of the muscle layers. The enhancing effect of stripping appears to be related to removal of a resistance to ion flow across the tissue. 相似文献
18.
Yuko Mori Masaaki Ando 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(4):387-392
Summary Both acetylcholine (ACh) and serotonin (5-HT) lowered the serosa-negative transepithelial potential difference (PD) and the short-circuit current (Isc), accompanied by a decrease in NaCl and water absorption across the eel intestine. These inhibitory effects of ACh and 5-HT were blocked by atropine, a muscarinic receptor antagonist, and ICS-205930, a 5-HT3 receptor antagonist, respectively. Even after blocking the ACh receptor with atropine, 5-HT inhibited the PD and Isc, and ACh lowered them after blocking the 5-HT receptor with ICS-205930, indicating that ACh and 5-HT act independently. Similar inhibition in the PD and the Isc was observed after electrical field stimulation (EFS) which is expected to release endogenous regulators. These effects of EFS were reduced by 70% after simultaneous addition of atropine and ICS-205930. Since atropine and ICS-205930 block ACh and 5-HT receptors, respectively, these results suggest that endogenous ACh and 5-HT are released by EFS.Abbreviations
ACh
acetylcholine
-
EFS
electrical field stimulation
-
5-HT
serotonin
-
I
sc
short-circuit current
-
PD
transepithelial potential difference
-
R
t
tissue resistance
-
TTX
tetrodotoxin 相似文献
19.
Lucas ML 《Journal of physiology and biochemistry》2008,64(1):69-88
Many forms of diarrhoeal disease, particularly so called “secretory” diarrhoeal disease are thought to arise by the active secretion of chloride ion from the enterocytes, creating an osmotic gradient for fluid movement into the small intestinal lumen. This model implies that normally occurring intestinal secretion is catastrophically enhanced by bacterial enterotoxins. This review advocates that neither normal nor abnormal intestinal secretion from the enterocytes occurs and that no competent proof for chloride secretion exists. Prior to 1970, the physiological evidence failed to support the concept of the formation of intestinal juice as a normal intestinal event. support the concept of the formation of intestinal juice as a normal intestinal event. The concept was later revived to explain the high rate of fluid entry into the lumen after exposure to cholera toxin. Much evidence has been advanced for the chloride secretion hypothesis, the dominant secretory paradigm after 1974, but is the evidence sufficiently compelling for it to be regarded as proving the chloride secretory model? The evidence falls into four categories and a fifth conjectural argument that proposes that an abnormal chloride ion channel in cystic fibrotic sufferers confers a natural selective advantage by preventing diarrhoeal disease. Secretion is putatively demonstrated by 1) showing that mass transfer of fluid is into the lumen (secretion) and not merely a failure to transport out of the lumen (failed absorption). Support is offered by 2) chloride ion flux measurementsin vitro in Ussing chambers and by 3) shortcircuit current measurements that are consistent with and purport to show chloride ion movement into the lumen. In addition, 4) pharmacological agents are identified that affect short-circuit current and these are assumed to be anti-secretory, consistent with the biochemical mechanism for secretion, confirmed wherever possible by mouse knock-out models. Finally, the proxy methods used to study water movement such as elevated short-circuit current measurements show these to be absent in cystic fibrotic patients. The enterocyte secretion hypothesis is challenged here on the basis of an examination of the methods used to show secretion, particularly after exposing the small intestine to heat stable enterotoxin (STa) fromE. coli. STa is thought to be secretory because fluid entry into the lumen is claimed, enhanced isotopic flux of chloride ion towards the lumen occurs, an increase in short-circuit current is found, preventable by various drugs that are deemed likely to be anti-secretory and also because the short-circuit current changes after STa are not seen in cystic fibrotic patients. Using volume recoveryin vivo, STa is found not to be secretory but only anti-absorptive. Hence, other techniques used to show secretion are not fit for that purpose. If STa is identified as secretory and yet no secretion occurs, how reliable is the evidence for other toxins being secretory when these methods are used? This review concludes that chloride ion secretion is unproven. A review of the literature indicates that secretion occurs not because epithelial cells actively pump water but by interdiction of fluid absorption, increased conductivity through tight junctions and an increased hydrostatic driving force through elevated capillary pressure. The exclusive focus on chloride secretion may explain the failure to develop antisecretory drugs over the last three decades. 相似文献
20.
Previous experiments in vitro revealed a transmural potential difference (PD) and a short-circuit current (Isc) across the rectal wall of Schistocerca gregaria, which were dependent on chloride ions in lumen. The present report shows that anoxia, dinitrophenol and cyanide inhibit DP and Isc, proving that the required energy derives from oxidative metabolism. Acetazolamide also inhibits DP and Isc. Ouabain, when in haemocoele, has also an inhibitory effect, not ascribable to a Na+K+ pump blocking action. It is suggested that HCO3? plays an important rôle in the active transport of Cl? from lumen to haemocoele and that ouabain may in some way inhibit chloride pumping. 相似文献