Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SEROSITIS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48Linked to original sources
PubMed1994

Mucosal acidification and an acid microclimate in the hen colon in vitro.

Experiments were performed on isolated, stripped colonic epithelia of low-salt-adapted hens (Gallus domesticus) in order to characterize acid secretion by this tissue. With symmetric, weak buffer solutions, colonic epithelia acidified both mucosal and serosal sides. Titration measurements of the mucosal acidification rate (pH-stat technique) averaged 1.63 +/- 0.25 microEq.cm-2.h-1. Mucosal acidification was also evident in colons from high-salt-adapted birds and in low-salt-adapted coprodeum, but was completely abolished in the high-salt coprodeum. Mucosal acidification by low-salt-adapted colonic epithelium was unaffected by sodium replacement, mucosal amiloride (10(-3) mol.l-1), and serosal ouabain (5 x 10(-4) mol.l-1), although all three treatments significantly reduced or reversed the short-circuit current. Acetazolamide (10(-3) mol.l-1, serosal) reduced mucosal acidification by 15% and simultaneously increased short-circuit current by a similar amount. Colonic epithelia incubated in glucose-free solutions had significantly lower acidification rates (0.59 +/- 0.13 microEq.cm-2.h-1, P < 0.002 versus controls) and addition of glucose (15 mmol.l-1), but not galactose, partially restored acidification to control levels. Anoxia (N2 gassing) completely inhibited short-circuit current, but reduced acidification by only 30%. A surface microclimate pH, nearly 2 pH units more acidic than the bath pH of 7.1-7.4, was measured in low-salt-adapted colon and coprodeum. The acid microclimate of both tissues was partially attenuated by adaptation to a high-salt diet. Colonic microclimate pH was dependent on the presence of glucose and sensitive to the bath pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗
PubMed1992

Transport of putrescine in the isolated rabbit intestine.

The transepithelial fluxes of putrescine were studied in sections of the three segments of rabbit intestine mounted in an Ussing chamber. The ileum exhibited the highest mucosal-to-serosal (Jms) and serosal-to-mucosal (Jsm) unidirectional fluxes of 1 mumol/l [3H]putrescine. Putrescine net flux (Jnet = Jms - Jsm) was deduced to be positive through the duodenum (Jnet = 53.40 +/- 14.30 pmol h-1 cm-2), not significantly different from zero through the jejunum (Jnet = 8.90 +/- 19.20 pmol h-1 cm-2) and negative through the ileum (Jnet = -34.30 +/- 13.80 pmol h-1 cm-2). Increasing putrescine concentration up to 10 mmol/l led to an increase in Jms, Jsm and Jnet without affecting the transport polarity in the ileum. The tissue retention of putrescine after 100 min was higher by the serosal side than by the mucosal side of the ileum. In parallel experiments, isolated pieces of ileum accumulated putrescine to a five- to sixfold concentration gradient by a ouabain-inhibitable mechanism. In contrast with arginine and in order of decreasing potency, putrescine, cystamine (a transglutaminase inhibitor), spermidine and spermine (1 mmol/l) reduced both unidirectional fluxes of putrescine across the ileum in the Ussing chamber. The latter effectors, except spermine, and N,N-dimethylcasein (1 mg/ml) led to an important, if not complete, suppression of putrescine secretion by the ileum, while the calmodulin antagonist melittin (0.3 micrograms/ml) reversed the polarity of polyamine transport, suggesting the involvement of transglutaminase in putrescine transport. We conclude that the heterogeneous pattern of putrescine transport along the small-intestinal epithelium constitutes an important feature of the regulation of polyamine concentrations in this tissue.

Animals↗
PubMed1992

Microelectrode determination of oxyntic cell pH in intact frog gastric mucosa. Effect of histamine.

Intracellular pH (pHi) of acid-secreting cells was measured in intact gastric fundus mucosa of Rana esculenta with double-barrelled pH microelectrodes. Tissues were mounted, serosal side up, between two half chambers and individual cells were impaled after microsurgical removal of the serosal muscle layer. Transepithelial potential difference (Vt) and resistance (Rt) as well as serosal cell membrane potential (Vs) and pHi were continuously recorded at rest (0.1 mmol/l cimetidine) or during stimulation (0.5 mmol/l histamine). During chamber perfusion with HCO3-/CO2-buffered Ringer solution of pHo = 7.36, Vt and Rt were -21.7, SD +/- 6.0 mV and 229 +/- 83 omega cm2 (n = 17) while Vs and pHi averaged -57.3 +/- 6.9 mV and 7.4 +/- 0.11 (n = 25). The latter value is considerably more alkaline than all recent pHi measurements obtained with microspectrofluorometric techniques on isolated cells, glands or intact tissue. The difference may in part be explained by use of HCO3(-)-free solutions in most of the previous studies because we observed that such solutions decrease pHi to 6.89 +/- 0.18 (n = 4). Again, in contrast to recent literature, application of histamine in HCO3-/CO2-buffered solution led to further transient alkalinization by 0.12 +/- 0.05 pH unit (n = 8). Since in accidental punctures of the gastric gland lumen we noticed that H+ secretion only began approximately 5 min after histamine application, we conclude that the histamine-induced initial alkalinization does not reflect stimulation of the H+/K+ ATPase pump.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Poorly selective cation channels in the apical membrane of A6 cells.

This paper describes a Ca(2+)-blockable, poorly selective cation pathway in the apical membrane of A6 epithelia. This pathway has properties that resemble the cation-selective channels in the toad urinary bladder and frog skin. Transepithelial short circuit currents (Isc) and power density spectra (PDS) of the fluctuations in current were recorded. The basolateral surface of the tissues was exposed to Cl- or SO4(2-) solutions with Na+ as the major cation. Ca(2+)-blockable inward oriented currents and Lorentzian noise were recorded with isotonic (215 mosmol/kg) mucosal Cl- and hypotonic (144 mos-mol/kg serosal SO4(2-) solution with Na+, K+, Rb+ or Cs+ as the major mucosal cation. Experiments with mucosal K+ demonstrated that the cation-selective channel was markedly activated by serosal hypotonicity. Effects of an increased electrical driving force were excluded on the basis of the results obtained with microelectrode experiments and transepithelial voltage clamping. Cell volume expansion induced by isotonic replacements of serosal sucrose by glycerol or urea also activated the cation-selective pathway. Furthermore, the presence of Cl- in the mucosal solution was a prerequisite for a sustained response to hypotonicity or replacements of the organic compounds. Moreover, we found that the cation-selective channels are mainly expressed in the cells during the early period of epithelial growth.

Animals↗
PubMed1977

Influence of hydrostatic pressure gradients on net transfer of sodium and water across isolated rat colonic mucosa.

1. The dependence of net transfer of water and sodium on hydrostatic pressure gradients from the serosal to the mucosal side was investigated in everted sacs of the stripped mucosa of the rat colon. 2. In the range of 3-20 cm H2O both, net sodium and water transfer were linearly dependent on hydrostatic pressure. The hydraulic permeability coefficient was 1.1 ml per gram dry weight, hour and cm H2O. At a pressure gradient of 5.8 cm H2O the net movement of water from the mucosal to the serosal side ceased. Above this pressure a net movement in the opposite direction occurs. Sodium net movement from the mucosal to the serosal side ceased at 11 cm H2O. The fluid, which appears-driven by higher values of hydrostatic pressure-on the mucosal side, is hypotonic. 3. Oxyphenisation increases the hydraulic permeability of the colonic epithelium. The fluid, which appears--driven by the hydrostatic pressure gradient--on the mucosal side, is isotonic.

Animals↗
PubMed1975

Intestinal transport of 3H-digitoxin in vitro incompatible with simple diffusion.

On everted jejunal segments of mice the transfer and tissue uptake of 3H-digitoxin, over a concentration range from 2 times 10(-10)--1 times 10(-4)M, was investigated from the mucosal ("m") to the serosal ("s") side as well as in the opposite direction. 1. The time course of the absorption of 3H-digitoxin and some other compounds investigated (glucose, urea, p-aminohippurate) gave evidence of functional integrity throughout the 75 min-periods of the experiments. 2. When 3H-digitoxin was applied to the mucosal side the permeability coefficient showed a dose-dependent increase but returned to lower values at higher concentrations. When 3H-digitoxin was administered to the serosal side the permeability coefficient showed a dose-dependent decrease at high concentrations. The ratio of both coefficients "m" leads to "s"/"s" leads to "m" increased dose-dependently from 0.4--2.6. 3. The uptake of 3H-digitoxin--applied on the serosal side--into the tissue was independent of dose. However, having administered 3H-digitoxin on the mucosal side the tissue accumulation was 2--5 fold higher and the tissue/medium (T/M) ratio increased within the concentration range from 3.0-9.0 4. Under DNP (1 mM) the asymmetry and dose dependence of the permeability and tissue uptake up 3H-digitoxin observed in controls were almost abolished. Therefore it is likely that the transfer of 3H-digitoxin in the intact intestine involves a mechanism more complex than simple diffusion. The existence of more than a two compartment system and/or the contribution of an active transport mechanism is suggested.

Aminohippuric Acids↗
PubMed1982

Stereospecific inhibition by ozolinone of stimulated chloride secretion in rabbit colon descendens.

The effects of the diuretic drug ozolinone on electrogenic Cl- secretion by rabbit colonic mucosa were investigated in vitro. Electrical properties and unidirectional Cl- fluxes were measured in stripped preparations mounted in Ussing-type chambers. After abolition of electrogenic Na+ absorption by amiloride (10(-4) mol/l) on the mucosal side electrogenic Cl- secretion was induced by addition of PGE1 (10(-6) mol/l, serosal side) and theophylline (10(-2) mol/l, both sides). Under these conditions, the monitored short-circuit current (Isc) equals the amount of Cl- secreted as evidenced by determination of unidirectional Cl- fluxes. After establishing a stable Cl- secretion its sensitivity to the enantiomers of the diuretic was studied. Only levorotatory (-)-ozolinone, but not the dextrorotatory (+)form, inhibited Cl- secretion on serosal application. This effect was fully accounted for by a reduction in the serosal-to-mucosal Cl- fluxes (JClsm). It was readily reversible and concentration-dependent with a Ki value of 6 x 10(-4) mol/l, but absent when the drug was added to the mucosal side. The results are in agreement with the hypothesis that loop diuretics inhibit a coupled NaCl entry mechanism across the baso-lateral membrane into colonic epithelial cells. This mechanism is though to account for Cl- influx into the cells.

Animals↗
PubMed1980

Transfer across mucosal epithelium, tissue content and metabolic fate of 125I-(ipodate-sodium) on isolated everted segments of rat small intestine.

1. Transfer and tissue content of 125I-radioactivity was measured after administration of 125I-(ipodate-sodium) to everted rat jejunal segments. 2. After having administered 10(-5) M 125I-(ipodate-sodium) on both sides of the everted sacs the S/M ratio of the concentration of 125I-radioactivity was 1.5 in jejunal segments and 2.3 in ileal segments. The tissue content was nearly equal for both segments. According to the apparent partition coefficient for ipodate-sodium at pH 7, the 125I-radioactivity is accumulated in the tissue about 10-fold. 3. Lowering of the temperature of the incubation medium from 37 degrees C to 15 degrees C prevents the building up of a concentration gradient between the serosal and the mucosal side on either jejunal and ileal segments whereas the tissue content of 125I-radioactivity was nearly unchanged. 4. With increasing concentrations (1.6--10(-6)--9.6-10(-4) M) of 125I-(ipodate-sodium) administered on the mucosal side the transfer and the tissue content of 125I-radioactivity were decreased. This appears to be a toxic effect since in jejunal segments also the S/M ratio for the concentration of glucose decreases. 5. The analysis of the 125I-radioactivity in the serosal fluid of jejunal segments showed that the bulk of the 125I-radioactivity was present in the aqueous phase and only 33% as the unchanged ipodate-sodium in the organic phase. 10% of the 125I-radioactivity must be attributed to inorganic iodine. The concentration of 125I-(ipodate-sodium) administered in the mucosal fluid only was 3.2-10(-6) M. At lower temperature (7 degrees C) the bulk of the 125I-radioactivity in the serosal fluid was found in the organic phase, i.e. as unchanged ipodate-sodium. 6. After the incubation of the aqueous phase with beta-glucuronidase or NaOH about 97% of the 125I-radioactivity could be extracted into the organic phase. This means that the bulk of the 125I-radioactivity in the aqueous phase is present as a conjugate, e.g. ester glucuronide of the unchanged ipodate. 7. Apparently, the process of the conjugation of ipodate-sodium in the mucosal cells is involved in the transfer of the 125I-radioactivity across the mucosal epithelium.

Animals↗
PubMed1986

Impairment of Na+ transport across frog skin by Tl+: effects on turnover, area density and saturation kinetics of apical Na+ channels.

Na+ transport across abdominal skin of the frogs, Rana temporaria and Rana esculenta was followed by measuring Na+-dependent short-circuit, current (INa) kinetics and INa fluctuations induced by triamterene, a diuretic. Exposure of the skin to serosal Tl+ led to a pronounced and irreversible drop in INa and INa-blocker noise. At low serosal Tl+ concentrations, we observed mainly a decrease in the apparent Michaelis constant for INa saturation while, at larger [Tl+], the maximal INa dropped irreversibly. Tl+ acts even when serosal Tl+ "transporters" like the Na+-K+ pump, or the K+ channel are nonfunctional. The rate constants for the triamterene/Na+ channel reaction were unchanged after Tl+ whereas the relaxation noise from channel blockage decreased in amplitude. Noise analysis in terms of a two-state blocking model suggested that Tl+ poisoning results in a small decrease in single-channel current through apical Na+ pathways, as well as in a drastic and irreversible drop in channel density. The impairment of Na+ transport by Tl+ can be attributed to the above cited concerted events at the level of the apical membrane.

Animals↗
PubMed1979

Transepithelial transport of K+, NH4+, inorganic phosphate and water by hen (Gallus domesticus) lower intestine (colon and coprodeum) perfused luminally in vivo.

The colon and coprodeum of anaesthetised laying hens was perfused luminally with solutions of varying compositions to elucidate the influence of three levels of dietary Na+ and of luminal fluid composition on transport of electrolytes and water. Net rates of secretion of K+ and absorption of NH4+ were increased in response to dietary Na+ depletion and increased luminal Na+ concentrations, but these fluxes were linked to Na+ transport and no dietary or perfusion treatment effects could be detected on them independently of effects on Na+ flux. Similar results were found for Na+-linked water absorption from isosmotic perfusates. Serosal-mucosal net osmotic flow with Na+-free perfusates was significantly reduced by Na+-depletion, but no significant dietary effect could be detected on the serosal-mucosal osmotic permeability coefficient. The reflexion coefficient was effectively unity. Mucosal-serosal inorganic phosphate flux was small. The flux was independent of Na+ flux and dietary Na+ levels, and apparently facilitated by serosalmucosal osmotic flow. The data allowed determination of the absorption/secretion in coprodeum and colon of the ions investigated, as compared to the renal excretion rate.

Ammonium Chloride↗
PubMed1981

Capacitive and inductive low frequency impedances of Necturus gallbladder epithelium.

The electrical impedance of Necturus gallbladder epithelium was analysed in the frequency range 0.24 Hz to 6,323 Hz. Under control conditions (NaCl-Ringer's on both sides), the impedance function yields a semicircle with depressed center. When serosal Na+ was replaced by K+, an inductive low frequency (LF) component appeared in the impedance locus. With KCl-Ringer on the mucosal side a second circular arc was observed at frequencies below 1 Hz. The resistive parts of the capacitive and inductive LF components increased after application of TAP+ to the mucosal side. Both LF features were abolished after application of 5 mM TEA+ to the mucosal medium as well as after acidification of the mucosal side. The LF components were depressed by addition of 5 mM Ba2+ to the mucosal solution. As TEA+ blocks apical K+ channels (Van Driessche and Gögelein 1978), it is concluded that the capacitive as well as the inductive LF components are related to transcellular K+ flow. With KCl-Ringer on the mucosal side, mucosa negative potentials increased the equivalent resistance and decreased the equivalent capacitance of the LF impedance. With serosal KCl-Ringer, negative potentials evoked a capacitive component which overlapped with the inductive component observed at open circuit conditions. Positive potentials, however, abolished the capacitive as well as the inductive LF component, elicited by mucosal or serosal KCl-Ringer, respectively. These results demonstrate that serosa to mucosa directed K+ flow causes an inductive LF feature and that mucosa negative potentials elicit a capacitive LF component.

Animals↗
PubMed1986

K+ -stimulated Na+ transport in frog-skin epithelia.

Increasing [K+] from 2.5 mmol/l to 115 mmol/l on the serosal side of the frog skin produces a rapid decrease of short-circuit current (Isc) that is followed, within a few minutes, by a recovery of Isc to near or above its control value. After isolation of the epithelium by a procedure involving collagenase treatment and physical removal of the corium, increasing serosal [K+] still produced a depression of Isc but no significant recovery phase. By itself, collagenase treatment reduced but did not eliminate the recovery phase. The recovery phase was also markedly depressed by the beta-adrenergic blocker oxprenolol, but not by propranolol, atropine or indomethacin. Amiloride, given during the recovery phase, caused Isc to reverse to a small outward value. These results suggest that the recovery phase of Isc seen in the response to increased serosal [K+] represents an increase in Na+ influx through amiloride-sensitive channels which is triggered by the release of an intermediary agent, possibly a beta-adrenergic agonist, from some structure in the corium.

Adrenergic beta-Antagonists↗
PubMed1986

Potassium microclimate at the mucosal surface of the proximal and the distal colon of guinea pig.

K+ concentrations were measured with K+ sensitive liquid ion exchanger microelectrodes in situ and in vitro in the mucus layer at the luminal cell surface of the proximal and the distal colon in guinea pig. In a first series of experiments K+ concentrations were increased in the luminal solution from 0 to 70 mmol X l-1; the serosal K+ concentrations were kept in vitro at 5.4 mmol X l-1. In the proximal colon mean K+ concentration in the microclimate was in vitro 7.9 +/- 3.5 mmol X l-1, and independent from mucosal concentrations. In the distal colon in vitro, and in situ in the proximal as well as in the distal colon, K+ concentrations in the microclimate were increased slightly when K+ concentrations were elevated in the luminal solution up to 70 mmol X l-1. In a second series of in vitro studies K+ concentrations were also altered in the serosal fluid. In the proximal and in the distal colon K+ concentrations increased linearly with elevated K+ concentrations in the serosal solutions. A temporarily interrupted mucosal blood flow resulted in a significant increase in the K+ concentration in the microclimate. A paracellular shunt pathway and a high preepithelial diffusion barrier for K+ would explain the observed K+ concentrations in the microclimate at the luminal cell surface.

Animals↗
PubMed1989

Transport properties of the basolateral membrane of the oxyntic cells in frog fundic gastric mucosa.

The conductive properties of the basolateral membrane of oxyntic cells (OC) of frog fundic gastric mucosa were investigated by utilizing the microelectrode technique. By examining the response of the basolateral cell membrane potential difference, Vcs, to sudden ion concentration changes in the serosal bath it was concluded that the basolateral membrane of OC has a high Ba2+-sensitive K+-conductance, and no Cl- -conductance both in resting (cimetidine) and in stimulated (histamine) state. The response of Vcs to serosal Cl- -removal, consisting in a slight hyperpolarization (anomalous Nernst response), could not be explained by possible permeability changes to K+ and Na+ since the potential response to Cl- was essentially preserved by blocking K+-permeability with Ba2+ and replacing all Na+ by choline. Conversely, hyperpolarization of Vcs after Cl- -free perfusion was abolished by exposure to HCO3- -free solution, indicating that HCO3- -ions are required at the serosal bath for Cl- to get his effect. It was investigated wether the effect of Cl- was due to an electrogenic Na+ (HCO3-)n/Cl- exchange mechanism on the basolateral membrane. Experiments showed that the potential response to HCO3- -removal and to Na+-removal, consisting in a depolarization of Vcs, was similar both in presence and in absence of Cl-. Furosemide (0.5 mmol/l) had no effect on steady Vcs and Vt. The electrophysiological analysis of the data led to excluding the involvement of Na-Cl, Na-2Cl and NaK-2Cl cotransports, and to including the existence of an electrogenic Na+(HCO3-)n/Cl- exchange process, while suggests the presence of an electroneutral Cl-/HCO3- exchange mechanism to explain Cl- -transport across the basolateral membrane of OC.

Animals↗
PubMed1980

Lactate and bicarbonate transport in rat and hamster jejuna incubated in vitro.

The transport of electrolytes into the serosal compartment of everted rat and hamster jejuna, incubated "in vitro" for 1 h, has been evaluated both at 38 degrees C and 28 degrees C. In order to determine the bicarbonate concentration in this compartment, pH and pCO2 were measured. It appears that, under both these experimental conditions, a relationship exists between lactate transport and pCO2 in the serosal side. A diffusion of undissociated lactic acid from the cellular into the serosal compartment is suggested. Oxygen consumption was approximately identical, at 28 degrees C, in both species. If the above assumption is correct, in the rat the anions which follow sodium during its active transport are mainly bicarbonate and chloride, while in the hamster jejunum, sodium is followed by chloride alone.

Animals↗
PubMed1982

The effect of inhibitors of folic acid absorption on the transfer rate constants in the rat everted proximal jejunum: a method for their evaluation from a three-compartment model.

When solute transfer through the intestinal in vitro everted sac preparation is described by a three-compartment system, solute transfer rate constants can be derived for the mucosal and serosal permeability barriers. A catenary variant has been presented as well as a mammillary one where paracellular movement of solute is additionally allowed for. The first order differential rate equations governing the change in solute concentration in all three compartments with respect to time have been solved and the explicit analytical solutions provided. Since these solutions are cumbersome to use in the estimation of the required rate constants, a least squares procedure has been applied directly to the differential form of the rate equations in order to derive the rate constants without recourse to the analytical solutions. Verification of the solutions and of the estimated rate constants was by substitution of the latter into the former to test the goodness of fit for folic acid absorption data. Both variants take into account the simultaneous fluid movement which occurs during absorption experiments and which complicates the interpretation of absorption data. The mammillary model showed that only 10% of folic acid movement could pass directly through the paracellular pathways and that the bulk of folate movement is probably through the epithelial cells. However the catenary model without paracellular movement gave just as good fit to the data and was used subsequently. Experiments investigating the effect of substances implicated in folate malabsorption were analyzed in terms of the catenary model for folic acid absorption, in order to investigate their effects on the transfer rate constants free from the complicating effects on fluid movement. When pronounced inhibition took place, as with methotrexate, the mucosal rate constants were reduced, whereas the serosal rate constants were elevated. Also, the forward (k12) mucosal rate constant correlated significantly with the overall folate transfer in contrast to the other rate constants. These observations are consonant with the concept of a mucosally sited entry step exerting a controlling influence over the transfer rate of folic acid rather than a serosally sited exit process and with the conclusion that this may be the site of action of substances causing folate malabsorption.

Animals↗
PubMed1982

Three-dimensional structure and cell kinetics at different sites of rat intestinal remnants during the early adaptive response to resection.

In this study the early phase of the morphological adaptation of rat ileum after a proximal resection of 60% has been studied using microdissection and cell labelling techniques. Resected rats and sham-operated controls were killed 2, 4, 6, 10 and 12 days after surgery. Intraperitoneal injections of 3H-thymidine were carried out 24 or 12 h prior to sacrifice. In the latter groups mitotic arrest was achieved by vincristine. A stereo-microscope was used to measure and calculate the following parameters: intestinal diameter; villus: height, width, breadth at base and apex, surface, enterocytes per 100 micrometers length, cell pool, number of villi and absorptive surface per mm2 serosal area; crypt: length, enteroblasts per 100 micrometers length and per column, cell columns and mitoses per crypt, cell pool, crypts, and mitoses per unit serosal area; cell kinetics: migration rate, villus transit time. To test the influence of treatments, postoperative time course and the location of the intestinal segment and their possible interactions, factorial analyses of variance were carried out on the parameters investigated. The main findings, demonstrated for the first time, were: 1. An increase in the villus surface which was achieved by proportional enlargement of villus geometry; 2. This increase in the villus surface led to an enlarged absorptive surface per unit serosal area; 3. A reduction of villus transit time of the individual enterocyte; 4. A most pronounced magnitude of adaptative response in the proximal remnants which was gradually diminished in aboral direction, and 5. A sequential course of adaptative response of the various crypt parameters investigated.

Animals↗
PubMed1982

Extracellular Ca2+ and the effect of antidiuretic hormone on the water permeability of the toad urinary bladder: an example of flow-induced alteration of flow.

The extracellular Ca2+ requirement for antidiuretic hormone (ADH) stimulation of water permeability in the toad urinary bladder has been critically examine. The polarity of the tissue was maintained with 1 mM Ca2+ in the mucosal bathing medium and a serosal bath nominally free of Ca2+. Under these conditions, ADH-induced osmotic water flow was inhibited by more than 60% while enhancement of the diffusional permeability to water was unaffected. Structural studies revealed that low serosal Ca2+ led to parallel alterations in epithelial architecture that amounted to a significant distortion of the osmotic water pathway. Prevention of these alterations, or restoration of normal cell-cell contact showed that the reduction of serosal Ca2+ did not restrict hormonal action per se, but that it resulted in a weakening of cell-cell junctions such that intercellular space distension during water flow occurred to a point where the geometric conditions for maintenance of osmotic flow were compromised. We conclude that extracellular Ca2+ is not a requirement for the molecular aspects of ADH action but that, in its absence, a direct measurement of ADH-induced osmotic flow proves to be an inaccurate index of the hormone-generated changes in epithelial transport characteristics. Under certain conditions the ADH-effect on the tissue's hydraulic permeability is probably best assessed by measurement of the diffusional permeability to water; although accuracy in this determination is difficult, it is not as strongly dependent on tissue geometry.

Animals↗