Cl Absorption Research Articles

CGMP and Ca2+ regulation of ion transport across the isolated porcine distal colon epithelium

Intact epithelium from the porcine distal colon was stripped of serosal muscle and mounted in Ussing chambers to investigate the regulation of Na, Cl, and K transport by guanosine 3',5'-cyclic monophosphate (cGMP) and elevations in intracellular [Ca2+]. Under voltage-clamped conditions cGMP (250 microM) produced an increase in tissue short-circuit current (Isc) that reached a maximal value within 10-20 min and remained elevated > 40 min. This response was associated with an inhibition of NaCl absorption and stimulation of Cl and K secretion. In the absence of Cl the Isc also slowly increased but returned to baseline values within 20 min. Bicarbonate removal from both serosal and mucosal solutions or serosal bumetanide (20 microM) reduced the effect of cGMP on Isc by approximately 40%. When performed simultaneously, these conditions reduced the cGMP response by approximately 60%. Transepithelial Na and Cl flux measurements indicated that serosal bumetanide blocked increased Cl secretion without effecting changes in NaCl absorption. In contrast, mucosal amiloride blocked the effects of cGMP on NaCl absorption but not Cl secretion. The cGMP Isc response was potentiated in the presence of 1 mM, but not 10 microM, amiloride. Moreover, 1 mM amiloride inhibited Isc under control conditions but was ineffective in the presence of cGMP. The Ca2+ ionophore ionomycin (3 microM) produced a transient increase in the Isc that was also associated with a decrease in transepithelial NaCl absorption and an increase in Cl and K secretion. In contrast to cGMP, the ionomycin Isc response was eliminated after Cl removal from the bath.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical inactivation of the nucleus tractus solitarius abolished hepatojejunal reflex in the rat

Jejunal electrolyte absorption was measured in the jejunal loop of anesthetized rats during an infusion of 9% NaCl solution via the portal vein. Net absorption of Na and Cl, and osmotality were significantly depressed by the portal 9% NaCl infusion. The decrease in net absorption was completely abolished by hepatic denervation. In addition, bilateral chemical inactivation of the nucleus tractus solitarius (NTS) by microinjection of kainic acid abolished the depressing effect of the portal venous infusion of 9% NaCl. These findings indicate that NTS is involved in the central pathway of the hepatojejunal reflex.

Exciton emission in BaFBr and BaFCl crystals

The emission of self-trapped excitons produced by vacuum ultraviolet excitation as well as X-ray excitation or photostimulation in BaFCl and BaFBr crystals was studied. The exciton emission bands at 4.2 and 5.15 eV in BaFBr and at 3.3 eV in BaFCl were observed upon irradiation into the Cl or Br exciton absorption bands. The 5.15 eV emission band in BaFBr thermally transforms to the 4.2 eV band with increasing temperature within the range 50-80 K. The 3.3 eV emission in BaFCl increases in the range 20-50 K in BaFCl, while the lifetime of the emission decreases. These facts indicate rather clearly the potential barrier between two different exciton configurations. The low-temperature exciton configuration was tentatively assigned to the Vk+e type and the other to F+H type.

Acidification stimulates chloride and fluid absorption across frog retinal pigment epithelium.

Radioactive tracers and a modified capacitance-probe technique were used to characterize the mechanisms that mediate Cl and fluid absorption across the bullfrog retinal pigment epithelium (RPE)-choroid. In control (HCO3/CO2) Ringer solution, 36Cl was actively absorbed (retina to choroid) at a mean rate of 0.34 mu eq.cm-2.h-1 (n = 34) and accounted for approximately 25% of the short-circuit current. Apical bumetanide (100 microM) or basal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) inhibited active Cl transport by 70 and 62%, respectively. Active Cl absorption was doubled, either by removing HCO3 from the bathing media or by elevating CO2 from 5 to 13%, and the increased flux was inhibited by apical bumetanide or basal DIDS. Open-circuit measurements of fluid absorption rate (Jv) and the net fluxes of 36Cl, 22Na, and 86Rb (K substitute) indicated that CO2-induced acidification stimulated NaCl and fluid absorption across the RPE. During acidification, bumetanide produced a twofold larger inhibition of Jv compared with control. Stimulation of net Cl absorption was most likely caused by inhibition of the the basolateral membrane intracellular pH-dependent Cl-HCO3 exchanger.

Effects of Deconjugated Bile Acids on Electrolyte and Nutrient Transport in the Rabbit Small Intestine In Vitro

To obtain new information on the poorly investigated mechanisms of the diarrheogenic effects of bile acids, we investigated the effects of the unconjugated bile acids chenodeoxycholate and ursodeoxycholate on the small intestine transport of electrolytes and nutrients in the rabbit jejunal and ileal mucosa mounted in vitro in Ussing or influx chambers. When added to the ileal mucosa at a concentration of 1 m M, both bile acids induced a secretory shift in ion transport; absorption of Na and Cl was abolished and secretion of bicarbonate was enhanced. No changes in short circuit current or electrolyte transport were observed when the bile acids were added to the jejunal mucosa. The addition of 1 m M chenodeoxycholate to the luminal side of the ileum induced a marked inhibition in the uptake of glucose, phenylala‐nine, and glutamic acid. A similar inhibition, though of a lesser magnitude, was also induced by both bile acids on jejunal nutrient transport. Further studies on the inhibitory effect of chenodeoxycholate on glucose influx showed that the inhibition was dose‐dependent; at 1 m M it was maximal and resulted in the complete abolition of the active component, with only the diffusional pathway still operative. We conclude that unconjugated bile acids act as secretagogues in the ileum and significantly blunt the active transport of nutrients in the small intestine. Both effects may well play a role in the diarrheogenic action of these bile acids.

Effects of Deconjugated Bile Acids on Electrolyte and Nutrient Transport in the Rabbit Small Intestine In Vitro

To obtain new information on the poorly investigated mechanisms of the diarrheogenic effects of bile acids, we investigated the effects of the unconjugated bile acids chenodeoxycholate and ursodeoxycholate on the small intestine transport of electrolytes and nutrients in the rabbit jejunal and ileal mucosa mounted in vitro in Ussing or influx chambers. When added to the ileal mucosa at a concentration of 1 mM, both bile acids induced a secretory shift in ion transport; absorption of Na and Cl was abolished and secretion of bicarbonate was enhanced. No changes in short circuit current or electrolyte transport were observed when the bile acids were added to the jejunal mucosa. The addition of 1 mM chenodeoxycholate to the luminal side of the ileum induced a marked inhibition in the uptake of glucose, phenylalanine, and glutamic acid. A similar inhibition, though of a lesser magnitude, was also induced by both bile acids on jejunal nutrient transport. Further studies on the inhibitory effect of chenodeoxycholate on glucose influx showed that the inhibition was dose-dependent; at 1 mM it was maximal and resulted in the complete abolition of the active component, with only the diffusional pathway still operative. We conclude that unconjugated bile acids act as secretagogues in the ileum and significantly blunt the active transport of nutrients in the small intestine. Both effects may well play a role in the diarrheogenic action of these bile acids.

Meal-stimulated canine jejunal ionic absorption. Influence of mucosal neural blockade.

The oral ingestion of a meal or the delivery of nutrients directly to the stomach or duodenum stimulates water and ion absorption from the proximal jejunal lumen. To further investigate this phenomenon, this study tested two hypotheses: (1) direct jejunal nutrient delivery stimulates jejunal absorption, and (2) the signal for jejunal absorption requires intact enteric neurotransmission and will therefore be altered by mucosal neural blockade with the local anesthetic bupivacaine. Intestinal absorption studies (N = 52) were performed on eight dogs with 25-cm jejunal Thiry-Vella fistulas (TVF) and feeding jejunostomies. Luminal perfusion with [14C]PEG was used to calculate TVF absorption of H2O, Na+, and Cl-. Six groups were randomly studied over 4 hr. Each group incorporated a basal hour, a TVF or jejunostomy treatment hour, and an oral (groups 1 and 3) or a jejunal (groups 4 and 6) meal stimulus. The oral and jejunal meals were isocaloric and of identical composition. Groups 1-3 had saline (as a control) or 0.75% bupivacaine applied to the lumen of the TVF. Groups 5 and 6 had 0.75% bupivacaine application to the feeding jejunostomy. Both the oral and the jejunal meal stimuli resulted in a significant proabsorptive response in the TVF. TVF bupivacaine reduced basal absorption but did not diminish the meal-induced proabsorptive response. Treatment of the jejunostomy with bupivacaine caused no change in basal or postmeal absorption in the TVF.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of barium Chloride on electrolyte transport across isolated colons from normal and Aldosterone-treated lizards (Gallotia Galloti)

Addition of BaCl2 to the solution bathing colons of normal lizards did not alter the absorptive Na+ flux, but did reverse the net absorption of Cl- to become net secretion. Cl- secretion resulted from an increase in its serosal-to-mucosal movement and was positively correlated to an increase in short-circuit current. Ba2+-induced short-circuit current was dependent on the presence of both Na+ and Cl- in the serosal medium. Ba2+-induced Cl- secretion could be reversed by serosal amiloride (10(­4) mmol l-1). Colons from acutely or chronically aldosterone-treated lizards exhibited a considerably higher short-circuit current, potential difference and net Na+ absorption than did untreated colons. Net Cl- transport was unaltered by acute treatment, but was totally abolished after chronic treatment. BaCl2 rapidly decreased the potential difference, short-circuit current and tissue conductance across colons from aldosterone-treated lizards. Net Na+ transport was markedly inhibited by Ba2+ in both acutely and chronically treated tissues, but barium did not change unidirectional or net Cl- fluxes in these. The present results support the following hypotheses: (1) that BaCl2 inhibits electrogenic Na+ absorption induced by acute or chronic aldosterone treatment and (2) that Ba2+ induces an electrogenic Cl- secretion by stimulating a basolateral Na+-dependent Cl- intake in normal but not in aldosterone-treated colons. This also suggests that aldosterone could exert an antisecretory influence in colonic epithelia.

Determination of Anions in Aqueous Solution by Measuring the Absorption of Radicals and Hydrated Electrons Using a UV Laser

The determination of anions in aqueous solution using an ArF laser is described. Chloride ion can be determined down to a level of 4×10-7M by measuring the absorption of Cl formed by ArF laser irradiation using a multiple-reflection method with a helium-cadmium laser (λ=325nm) as the monitoring light source. Br-, I-, SCN-and SO42-were determined by measuring the absorption of radicals or hydrated electrons formed upon UV laser irradiation with detection limits of 4×10-7, 4×10-7, 1×10-6-and 1×10-4M, respectively.

Digestive Tract Absorption of Polychlorinated Dibenzo- p-dioxins, Dibenzofurans, and Biphenyls in a Nursing Infant

The digestive tract absorption of environmental contaminants is an important but poorly understood parameter in contaminant risk assessments. The net absorption of polychiorinated dibenzo- p-dioxins, dibenzofurans, and biphenyls in a nursing infant was measured under natural conditions over 12 days. The levels of the substances in the mother′s milk were typical for Germany. It was found that for almost all congeners over 90% of the ingested compound was absorbed. This indicates that the common assumption of 100% absorption in nursing infants is reasonable. No firm conclusions could be drawn regarding the absorption of Cl 7- and Cl 8DD/F due to high blank levels in the cotton diapers used.

Single‐Dose Safety and Pharmacokinetics of a Potential Cognition‐Enhancing Compound, CL 275,838, in Healthy Volunteers

The pharmacokinetics and safety of CL 275,838, a potential cognition-enhancing compound, were studied after single escalating oral doses first in young healthy male volunteers and then in old (60-74 years) and very old (over 75 years) volunteers of both sexes. In all age groups absorption of CL 275,838 was rapid as assessed by the mean time to reach maximum plasma concentrations (Cmax) which averaged 1-2 hr, regardless of the dose administered. In young male volunteers both Cmax and area under the curve (AUC) increased proportionally with dose from 10 to 100 mg. Mean elimination half-lives (t1/2) of the parent compound (18-21 hr) and of its circulating metabolites II (20-22 hr) and IV (27-30 hr) were well comparable for the doses tested (50 and 100 mg). Age did not appreciably affect plasma Cmax of CL 275,838 or its two metabolites. Mean AUC and elimination half-life did not appreciably differ between old and very old subjects given 50 mg CL 275,838, with the limitations dictated by the small number of elderly subjects examined. Compared with younger volunteers receiving comparable doses, however, the elderly had higher mean plasma AUC of the unchanged compound and its two metabolites, although the parameter varied widely between subjects. The mean elimination t1/2 (+/- SD) was longer in the elderly (38.8 +/- 19.6, 50.5 +/- 24.5 and 41.7 +/- 12.1 hr, respectively, for the parent compound and its metabolites II and IV) than in the young subjects. The cause(s) of these variations and the possible clinical implications remain to be established.(ABSTRACT TRUNCATED AT 250 WORDS)

ANP inhibits NaCl absorption and elicits Cl secretion in porcine colon: evidence for cGMP and Ca mediation.

The effects of atrial natriuretic peptide (ANP) on ion transport were examined in the isolated, short-circuited proximal colon epithelium of the pig. Addition of ANP to the serosal solution decreased the rate of neutral Na and Cl absorption and elicited electrogenic Cl secretion. Amiloride, at a concentration that inhibits Na-H exchange, produced an identical inhibition of Na transport and abolished the ANP-induced decrease in Na absorption. In contrast, serosal addition of bumetanide, an inhibitor of Na-K-2Cl cotransport, partially inhibited the short-circuit current (Isc) response to ANP. Whereas 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) produced qualitatively similar effects as ANP, relatively high concentrations of N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) or prostaglandin E2 were required to alter NaCl transport. Furthermore, incubation of colonic mucosa with ANP induced a threefold increase in cGMP content, whereas cAMP was unaffected. The ANP-induced Cl secretion and Isc were diminished with tetrodotoxin and verapamil, whereas these agents were without effect on the ANP-induced inhibition of Na and Cl absorption. Results indicate that ANP inhibits net colonic absorption of ions by antiabsorptive and secretory mechanisms that are dependent on both cGMP and Ca.

The effect of colitis on large-intestinal electrolyte transport in early childhood.

The large intestine plays an important role in the salvage of electrolytes and water, although little is known of its function in early childhood in health or in disease. Using an in vitro voltage clamp technique, we have measured bidirectional sodium (Na) and chloride (Cl) fluxes (J), electrical potential difference (PD), short circuit current (Isc), and tissue resistance (R) in 10 pairs of healthy human infant left colon and four pairs of inflamed colon. In healthy tissue there was net Na and Cl absorption with JNa net approximating Isc. In contrast, inflamed colon exhibited significant reductions in PD, Isc, and R and increases in net serosa to mucosa flux of Na and Cl (JNasm and JClsm) resulting in net Na and Cl secretion. These results suggest that Na and Cl absorption in left colon is highly efficient in young children and that mucosal inflammation may seriously impair the colon's ability to conserve salt and water.

The Effect of Colitis on Large‐Intestinal Electrolyte Transport in Early Childhood

SummaryThe large intestine plays an important role in the salvage of electrolytes and water, although little is known of its function in early childhood in health or in disease. Using an in vitro voltage clamp technique, we have measured bidirectional sodium (Na) and chloride (C***l) fluxes (J), electrical potential difference (PD), short circuit current (Isc), and tissue resistance (R) in 10 pairs of healthy human infant left colon and four pairs of inflamed colon. In healthy tissue there was net Na and C***l absorption with JNa net approximating Isc. In contrast, inflamed colon exhibited significant reductions in PD, Isc, and R and increases in net serosa to mucosa flux of Na and Cl (JNasm and JClsm) resulting in net Na and Cl secretion. These results suggest that Na and Cl absorption in left colon is highly efficient in young children and that mucosal inflammation may seriously impair the colon's ability to conserve salt and water.

Regional adrenergic regulation of ion transport across the isolated porcine gallbladder

The regional transport properties of the porcine gallbladder epithelium were studied using Ussing chambers in which tissues were bathed in porcine Ringer solution. Under basal conditions, tissues from the neck absorbed Na and Cl. Fundic tissues also absorbed Na, but net Cl transport was not different from zero. Serosal norepinephrine (NE; 0.1 microM) stimulated Na and Cl absorption in the neck but only Cl absorption in the fundus. The effects of NE on Na and Cl transport were blocked by pretreatment with yohimbine, suggesting that alpha 2-adrenoceptors mediate the transport-related actions of this neurotransmitter. Serosal isoproterenol (0.1 microM) produced a tetrodotoxin-insensitive, propranolol-sensitive increase in the short-circuit current (Isc) in fundic tissues but not in tissues from the neck. The beta 2-adrenergic agonist salbutamol produced a response similar to that of isoproterenol. However, the beta 1-adrenergic agonist dobutamine had no effect. Isoproterenol was 5.8-fold more potent than salbutamol in increasing the Isc. A possible explanation for the regional effects of beta-agonists is that beta-adrenoceptors are localized to epithelial cells in the fundic region. These results and results obtained previously suggest regional differences in basal Na and Cl transport across the porcine gallbladder epithelium and that both alpha 2- and beta 2-adrenoceptors act to regulate ion transport in this tissue.

Effects of acute respiratory acidosis on water and electrolyte transport in the human ileum.

Animal experiments have shown that acute respiratory acidosis stimulates water, Na and Cl absorption and HCO3 secretion in the ileum. The aim of this study was to investigate whether the human ileum also responds to changes in systemic acid-base balance. Seven healthy volunteers (mean age 24, range 21-29 years) underwent segmental ileal perfusion using a multi-lumen tube assembly with a proximal occluding balloon. A 30 cm test segment was perfused under steady state conditions with a plasma-like electrolyte solution containing PEG as a non-absorbable volume marker. After a control period, respiratory acidosis (blood pCO2 56.2 mmHg, pH 7.29 and [HCO3] 26.4 mmol l-1) was induced by CO2-breathing over a period of 50 min. Acute respiratory acidosis stimulated net HCO3 secretion in patients secreting HCO3 and reduced absorption in patients exhibiting net HCO3 absorption. These changes were immediate and appeared to be at least partly reversible. Net water, Na, K and Cl movement were not affected. The data suggest that HCO3 transport in the human ileum responds to acute respiratory acidosis.

Effects of ET-1 on water and chloride transport in cortical collecting ducts of the rat.

Endothelin-1 (ET-1) is known as a vasoconstrictor peptide. However, recent reports suggested the effects on the transport of renal tubule. We previously reported that ET-1 inhibited arginine vasopressin (AVP)-dependent adenosine 3',5'-cyclic monophosphate in rat collecting ducts. Physiologically, ET-1 reversibly and significantly inhibited AVP-stimulated water permeability in inner medullary collecting duct (IMCD). We therefore investigated the effects on water and electrolyte transport in rat cortical collecting ducts (CCD), where Na and Cl are actively reabsorbed more than in IMCD. Pathogen-free male Sprague-Dawley rats weighing 80-120 g were used after treatment with deoxycorticosterone pivalate for 1-2 wk. Isolated CCD were microperfused in vitro. The Cl concentration was measured by a continuous-flow ultra-microcolorimeter, and the raffinose concentration was measured as a volume marker by a continuous-flow ultra-microfluorometer. In the presence of 10(-9) M AVP, 10(-8) M ET-1 significantly inhibited fluid absorption (nl.mm-1 x min-1) from 0.25 +/- 0.02 to 0.15 +/- 0.05 (mean +/- SE, n = 6, P < 0.01), Cl absorption (pmol.mm-1 x min-1) from 30. 6 +/- 2.8 to 14.9 +/- 4.0 (P < 0.01), and potential difference (mV) from -5.4 +/- 1.3 to -4.0 +/- 1.2 (P < 0.01). Similar results were obtained in the lower concentration of 10(-10) M AVP and 10(-10) M ET-1. As for the osmotic water permeability (microns/s), 10(-8) M ET-1 significantly inhibited this from 320.1 +/- 50.9 to 202.1 +/- 42.2 (n = 7, P < 0.01) in the presence of 10(-9) M AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluid and electrolyte transport by cultured human airway epithelia.

An understanding of the fluid and electrolyte transport properties of any epithelium requires knowledge of the direction, rate, and regulation of fluid transport and the composition of the fluid. Although human airway epithelial likely play a key role in controlling the quantity and composition of the respiratory tract fluid, evidence for such a role is not available. To obtain such knowledge, we measured fluid and electrolyte transport by cultured human nasal epithelia. Under basal conditions we found that epithelia absorbed Na+ and fluid; both processes were inhibited by addition of amiloride to the mucosal surface. These data suggest that active Na+ absorption is responsible for fluid absorption. Interestingly, Na+ absorption was not accompanied by the net absorption of Cl-; some other anion accompanied Na+. The combination of cAMP agonists and mucosal amiloride stimulated the secretion of NaCl-rich fluid. But surprisingly, the response to cAMP agonists in the absence of amiloride showed substantial intersubject variability: cAMP stimulated fluid secretion across some epithelia, for others, cAMP stimulated fluid absorption. The explanation for the differences in response is uncertain, but we speculate that the magnitude of apical membrane Na+ conductance may modulate the direction of fluid transport in response to cAMP. We also found that airway epithelial secrete H+ and absorb K+ under basal conditions; both processes were inhibited by cAMP agonists. Because the H+/K(+)-ATPase inhibitor, SCH 28080, inhibited K+ absorption, an apical membrane H+/K(+)-ATPase may be at least partly responsible for K+ and H+ transport. However, H+/K+ exchange could not entirely account for the luminal acidification. The finding that cAMP agonists inhibited luminal acidification may be explained by the recent finding that cAMP increases apical HCO3- conductance. These results provide new insights into how the intact airway epithelium may modify the composition of the respiratory tract fluid.

Role of Na-dependent Cl/HCO3 exchange in basolateral Cl transport of rabbit proximal tubules.

To analyze the rate of basolateral Cl exit and the magnitude and relative contributions of KCl cotransport and Na-dependent and -independent Cl/HCO3 exchange to Cl exit across the basolateral membrane (BLM) during transcellular Cl absorption, rabbit proximal convoluted tubules (PCT) were perfused with high-Cl, low-HCO3 plus formate solutions and bathed with plasma ultrafiltrate-like plus formate solutions. The initial rates of intracellular Cl activity (AiCl) reduction following bath Cl removal were compared when bath Cl was 0, when bath Na and Cl were 0, and when bath HCO3 and Cl were 0. The initial rate of AiCl reduction following bath Cl removal was 4.4 +/- 0.4 mM/s. After bath Na and Cl removal, this rate was reduced to 25.1 +/- 5.0%. After bath HCO3 and Cl removal, it was reduced to 18.0 +/- 4.8%. The difference between bath Na and Cl removal and bath HCO3 and Cl removal was not significant. Cl efflux following bath HCO3 and Cl removal may be due to a KCl symporter. The contribution of a KCl symporter was examined by raising bath K to 20 mM, thus eliminating the chemical driving force for KCl exit. After bath K increase, the initial rate of AiCl increase was 0.057 +/- 0.005 mM/s. These data suggest that Cl efflux at BLM of rabbit PCT is 1) large enough to explain transcellular Cl transport, 2) predominately due to an Na-dependent Cl/HCO3 exchanger, and 3) negligibly due to an Na-independent Cl/HCO3 exchanger or a KCl symporter.

Rice genotypes differing in salt tolerance II. Short‐term kinetics of NaCl absorption and translocation in intact plants

Abstract Two pairs of contrasting rice genotypes, each pair having similar general characteristics but differing in their tolerance to salt, were compared in short‐term experiments of NaCl absorption and translocation in intact plants. At low external NaCl concentration (0.1 mM), the absorption of Na was passive with a constant net influx rate (In), while the absorption of Cl was an active process obeying Michaelis‐Menten kinetics. At both low and high external NaCl concentrations (0.1 and 50 mM), salt‐tolerant ‘Pokkali’ had significantly lower rates of Na and Cl absorption than did salt‐sensitive ‘Peta’, although another moderately salt‐tolerant genotype, ‘IR 29725–25–22–3‐3–3’, did not differ from its salt‐sensitive counterpart, ‘IR 5’. For both pairs of the plants, translocation rates of Na and Cl were significantly lower in the salt‐tolerant genotypes than in the salt‐sensitive ones. It was concluded that exclusion of Na and/or Cl from the shoots may involve both absorption and translocation component...