Regulation of bicarbonate transport in rabbit ileum: pH stat studies

1989 ◽  
Vol 257 (4) ◽  
pp. G607-G615 ◽  
Author(s):  
J. H. Sellin ◽  
R. Desoignie
Keyword(s):  
Short Circuit ◽  
Exchange Process ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Bicarbonate Transport ◽  
Bicarbonate Secretion ◽  
Acid Base Balance ◽  
Rabbit Ileum ◽  
Ph Stat

Although it is well recognized that the ileum secretes bicarbonate, understanding of the mechanisms of the transport of this ion has been limited by the inability to measure fluxes in vitro. However, by clamping the bathing fluid at a set pH using a pH stat system, accurate measurements of bicarbonate movement can be made. Bicarbonate transport in rabbit ileum in vitro was measured by simultaneously employing both the pH stat and short-circuit techniques. The role of acid-base balance was assessed by systematically altering buffer bicarbonate concentration, pH, and partial pressure of CO2 (PCO2). Bicarbonate secretion was strongly correlated with both serosal [HCO3-] (r = 0.824, P less than 0.01) and serosal pH (r = 0.793, P less than 0.01). Bicarbonate absorption was not significantly altered by mucosal [HCO3-], pH, or PCO2. Paracellular movement of bicarbonate, as assessed by voltage clamping and diffusion potential experiments, did not appear to be a major component of transcellular transport. Epinephrine stimulated bicarbonate absorption significantly, both in Cl-containing and Cl-free Ringer solution but did not alter bicarbonate secretion. Epinephrine-induced decreases in short-circuit current were correlated with enhanced bicarbonate absorption. Bicarbonate secretion was inhibited by serosal chloride and serosal bumetanide; mucosal chloride stimulated bicarbonate secretion. Mucosal chloride did not affect bicarbonate absorption. Glucocorticoids enhanced both bicarbonate absorption and secretion. These results suggest that there are discrete apical and basolateral transport mechanisms that regulate bicarbonate transport. Bicarbonate secretion may be mediated by a basolateral bumetanide-sensitive, chloride-inhibitable transporter and by an apical chloride-bicarbonate exchange process.

Bicarbonate secretion by rabbit proximal colon

1986 ◽  
Vol 251 (4) ◽  
pp. G436-G445 ◽  
Author(s):  
S. K. Sullivan ◽  
P. L. Smith
Keyword(s):  
Transport Process ◽  
Short Circuit ◽  
Proximal Colon ◽  
Bathing Solution ◽  
Bicarbonate Secretion ◽  
Rabbit Ileum ◽  
Ussing Chambers ◽  
Ph Stat ◽  
Dependent Mechanism

Stripped segments of proximal colon (1-6 cm distal to the ampulla caecalis coli) were studied in vitro in Ussing chambers under short-circuit conditions using the pH-stat technique. With glucose and HCO3-CO2 present in the serosal bathing solution only, proximal colon alkalinizes the luminal bathing solution at a rate of 2.1 +/- 0.2 mu eq X h-1 X cm-2 (n = 36). With HCO3-CO2 present in the luminal bathing solution alone, proximal colon does not significantly acidify or alkalinize the serosal bathing solution. Addition of glucose (10 mM) to the luminal bathing solution abolished luminal alkalinization. Removal of HCO3 and CO2 from the serosal bathing solution or replacement of O2 with N2 also abolished luminal alkalinization. Acetazolamide (0.1 mM) added to both bathing solutions did not alter the rate of luminal alkalinization. Ion-replacement studies revealed that the alkalinization process was highly dependent on the presence of Na in the bathing solutions and much less dependent on the presence of Cl. Furthermore, ouabain (0.1 mM) significantly reduced luminal alkalinization. As in rabbit ileum, serosal epinephrine (0.1 mM) did not alter luminal alkalinization but increased serosal alkalinization by a Na-dependent mechanism. These results suggest that luminal alkalinization results from a Na-dependent, active transcellular HCO3 transport process and that a Na-dependent HCO3 absorptive process is activated by adrenergic stimuli.

Protein kinase C potentiates cAMP-stimulated mouse duodenal mucosal bicarbonate secretion in vitro

2004 ◽  
Vol 286 (5) ◽  
pp. G814-G821 ◽  
Author(s):  
Bi-Guang Tuo ◽  
Jimmy Y. C. Chow ◽  
Kim E. Barrett ◽  
Jon I. Isenberg
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Duodenal Mucosa ◽  
Bicarbonate Secretion ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Ussing Chambers ◽  
Duodenal Bicarbonate Secretion

PKC has been shown to regulate epithelial Cl- secretion in a variety of models. However, the role of PKC in duodenal mucosal bicarbonate secretion is less clear. We aimed to investigate the role of PKC in regulation of duodenal mucosal bicarbonate secretion. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers using a pH-stat technique. PKC isoform expression and activity were assessed by Western blotting and in vitro kinase assays, respectively. PMA (an activator of PKC) alone had no effect on duodenal bicarbonate secretion or short-circuit current ( Isc). When PMA and dibutyryl-cAMP (db-cAMP) were added simultaneously, PMA failed to alter db-cAMP-stimulated duodenal bicarbonate secretion or Isc ( P > 0.05). However, a 1-h preincubation with PMA potentiated db-cAMP-stimulated duodenal bicarbonate secretion and Isc in a concentration-dependent manner (from 10-8 to 10-5M) ( P < 0.05). PMA preincubation had no effects on carbachol- or heat-stable toxin-stimulated bicarbonate secretion. Western blot analysis revealed that PKCα, -γ, -ϵ, -θ, -μ, and -ι/λ were expressed in murine duodenal mucosa. Ro 31–8220 (an inhibitor active against PKCϵ, -α, -β, and -γ), but not Gö 6983 (an inhibitor active against PKCα, -γ, -β, and -δ), reversed the potentiating effect of PMA on db-cAMP-stimulated bicarbonate secretion. PMA also time- and concentration-dependently increased the activity of PKCϵ, an effect that was prevented by Ro 31–8220 but not Gö 6983. These results demonstrate that activation of PKC potentiates cAMP-stimulated duodenal bicarbonate secretion, whereas it does not modify basal secretion. The effect of PKC on cAMP-stimulated bicarbonate secretion is mediated by the PKCϵ isoform.

Effect of acetazolamide on sodium and chloride transport by in vitro rabbit ileum

1975 ◽  
Vol 228 (6) ◽  
pp. 1808-1814 ◽  
Author(s):  
HN Nellans ◽  
RA Frizzell ◽  
SG Schultz
Keyword(s):  
Cyclic Amp ◽  
Chloride Transport ◽  
Short Circuit ◽  
Electrical Potential ◽  
Direct Interaction ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Membrane Component ◽  
Rabbit Ileum

Acetazolamide (8 mM) aboishes active Cl absorption and inhibits but does not abolish active Na absorption by stripped, short-circuited rabbit ileum. These effects are not accompanied by significant changes in the transmural electrical potential difference or short-circuit current. Studies of the undirectional influxes of Na andCl indicate that acetazolamide inhibits the neutral, coupled NaCl influx process at the mucosal membranes. This action appears to explain the observed effect of acetazolamide on active, transepithelial Na and Cl transport. Acetazolamide did not significantly inhibit either spontaneous or theophylline-induced Cl secretion by this preparation, suggesting that the theophylline-induced secretion may not simply be due tothe unmasking of a preexisting efflux process when the neutral influx mechanism is inhibited by theophylline. Finally, inhibition of the neutral NaCl influx process by acetazolamide does not appear to be attributable to an inhibition of endogenous HCO3production or an elevation in intracellular cyclic-AMP levels. Instead, it appearstheat the effect of acetazolamide is due to a direct interaction with a membrane component involved in the coupled influx process.

An Investigation of the Role of Possible Neural Mechanisms in Cholera Toxin-Induced Secretion in Rabbit Ileal Mucosa in Vitro

1989 ◽  
Vol 77 (2) ◽  
pp. 161-166 ◽  
Author(s):  
K. J. Moriarty ◽  
N. B. Higgs ◽  
M. Woodford ◽  
L. A. Turnberg
Keyword(s):  
Cholera Toxin ◽  
Fluid Transport ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Rabbit Ileum ◽  
Ileal Mucosa

1. Cholera toxin stimulates intestinal secretion in vitro by activation of mucosal adenylate cyclase. However, it has been proposed that cholera toxin promotes secretion in vivo mainly through an indirect mechanism involving enteric neural reflexes. 2. We examined this hypothesis further by studying the influence of neuronal blockade on cholera toxin-induced changes in fluid transport across rabbit ileum in vitro. Mucosa, stripped of muscle layers, was mounted in flux chambers and luminal application of crude cholera toxin (2 μg/ml) caused a delayed but sustained rise in the short-circuit current, electrical potential difference and Cl− secretion. Pretreatment with the nerve-blocking drug, tetrodotoxin (5 × 10−6 mol/l serosal side), failed to influence the secretory response to cholera toxin, and addition of tetrodotoxin at the peak response to cholera toxin also had no effect. 3. That tetrodotoxin could block neurally mediated secretagogues was confirmed by the demonstration that the electrical responses to neurotensin (10−7 mol/l and 10−8 mol/l) were blocked by tetrodotoxin (5 × 10−6 mol/l). Furthermore, the response to cholera toxin of segments of ileum, which included the myenteric, submucosal and mucosal nerve plexuses, was not inhibited by tetrodotoxin. 4. We conclude that cholera toxin-induced secretion in rabbit ileum in vitro is not mediated via a neurological mechanism.

Methylprednisolone increases absorptive capacity of rabbit ileum in vitro

1983 ◽  
Vol 245 (4) ◽  
pp. G562-G567 ◽  
Author(s):  
J. H. Sellin ◽  
R. C. DeSoignie
Keyword(s):  
Ion Transport ◽  
Absorptive Capacity ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Ion Flux ◽  
Rabbit Ileum ◽  
Transport Pathways ◽  
Na Pump ◽  
Intestinal Ion Transport

The effect of glucocorticoids on intestinal ion transport was studied in ileum in vitro from control and methylprednisolone (MP)-treated (40 mg im for 2 days) rabbits under the following conditions: a) basal rates of Na and Cl transport, b) the response to an individual absorptive stimulus (alanine, glucose, or epinephrine), and c) the response to a combination of the three absorptive stimuli. The results indicate that MP 1) increases basal absorption of Na and Cl and secretion of bicarbonate (as measured by residual ion flux), 2) does not alter the specific transport pathways stimulated by maximal doses of alanine, glucose, or epinephrine, but 3) significantly increases the absorptive capacity of ileum. After addition of combined alanine, glucose, and epinephrine, MP-treated ileum absorbed 15.8 mueq X cm-2 X h-1 Na (vs. 6.6 in controls, P less than 0.001) and 9.5 mueq X cm-2 X h-1 Cl (vs. 4.1 in controls, P less than 0.005). Additionally MP did not alter the Na dependence of either the short-circuit current or Cl absorption found in controls, although there appears to be a portion of residual ion flux insensitive to epinephrine inhibition. These data suggest that the MP-induced increase in absorptive capacity is due to an increase in a postapical transport step, most probably the Na pump.

cGMP modulation of ileal ion transport: in vitro effects of Escherichia coli heat-stable enterotoxin

1982 ◽  
Vol 243 (1) ◽  
pp. G36-G41 ◽  
Author(s):  
S. Guandalini ◽  
M. C. Rao ◽  
P. L. Smith ◽  
M. Field
Keyword(s):  
Escherichia Coli ◽  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Rabbit Ileum ◽  
Heat Stable ◽  
Transport Effects ◽  
In Vitro Effects ◽  
Nonadditive Effects

Diarrheagenic strains of Escherichia coli have been shown to produce a heat-stable enterotoxin (ST) that simulates guanylate cyclase, increases short-circuit current (Isc), and inhibits active Cl absorption in the intestine. In rabbit ileum, the ion transport effects are smaller than those produced by cAMP-related agonists. Because ST may be a selective cGMP agonist, we further explored its mode of action in rabbit ileum. ST inhibits net Na and net Cl absorption. ST also inhibits the same fraction of Cl influx across the brush border that theophylline inhibits. At maximal doses, ST and 8-bromo-cGMP (8-Br-cGMP) had nearly equal, nonadditive effects of Isc that were about 66% of that produced by 8-Br-cAMP. ST increased mucosal cGMP concentration 16-fold, whereas epinephrine, an inhibitor of secretion, increased cGMP concentration by only 30%. This is insufficient to alter ion transport because doses of ST that increased cGMP concentration by 100% failed to alter Cl fluxes. Furthermore, epinephrine did not increase cGMP concentration in isolated enterocytes. We conclude that 1) cGMP mediates ST effects on ion transport, and 2) although ST and cAMP-related agonists have the same antiabsorptive effects, ST is less effective in stimulating electrogenic Cl secretion.

Effect of sulfidopeptide leukotrienes D4 and E4 on ileal ion transport in vitro in the rat and rabbit

1988 ◽  
Vol 255 (2) ◽  
pp. G175-G183 ◽  
Author(s):  
P. L. Smith ◽  
D. P. Montzka ◽  
G. P. McCafferty ◽  
M. A. Wasserman ◽  
J. D. Fondacaro
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Bathing Solution ◽  
Na Transport ◽  
Rabbit Ileum ◽  
Rat Ileum ◽  
Ussing Chambers ◽  
Meclofenamic Acid ◽  
Acid Metabolites

Effects of leukotrienes D4 and E4 (LTD4 and LTE4) on electrolyte transport were examined, employing stripped segments of rat and rabbit ileum mounted in Ussing chambers. Addition of LTD4 or LTE4 to the serosal but not the mucosal bathing solution elicited a transient increase in short-circuit current (Isc) with maximal responses seen at 10(-5) M and 10(-8) M in rat and rabbit respectively and a sustained decrease in transepithelial conductance (Gt) in the rat only. In the rat, Cl replacement, reduction of bathing solution [Ca2+] to 1 microM or pretreatment with 1 microM indomethacin or meclofenamic acid inhibited the LTD4- or LTE4-induced Isc changes with no effect on the decrease in Gt. LTD4 (10 microM) transiently increased net Cl secretion and produced a sustained decrease in both unidirectional and net Na transport and mucosal-to-serosal Cl flux in rat ileum. The decrease in unidirectional Na fluxes is accounted for predominantly by a change in the potential independent flux of Na. These results suggest that the increase in Isc in both rat and rabbit is mediated by arachidonic acid metabolites, whereas the decrease in Gt and net Na absorption in rat ileum is mediated by a cyclooxygenase-independent pathway.

alpha 2-Adrenergic receptor regulation of ion transport in rabbit ileum

1982 ◽  
Vol 242 (3) ◽  
pp. G237-G242 ◽  
Author(s):  
E. B. Chang ◽  
M. Field ◽  
R. J. Miller
Keyword(s):  
Ion Transport ◽  
Adrenergic Receptor ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Maximal Effect ◽  
Rabbit Ileum ◽  
Ileal Mucosa ◽  
Receptor System ◽  
Alpha Adrenergic Receptors

Catecholamines are known to decrease short-circuit current (Isc), stimulate NaCl absorption, and inhibit HCO3 secretion in rabbit ileal mucosa in vitro. These effects appear to be mediated by alpha-adrenergic receptors because they are partially blocked by phentolamine and not by propranolol. To further characterize this receptor system, we determined the interactions of epinephrine (Epi) with alpha-subtype-selective antagonists. Prazosin (PZ), a specific alpha 1-antagonist, did not alter the Epi dose-response curve at concentrations up to 10(-5) M. Yohimbine (YO), a specific alpha 2-antagonist, completely inhibited the Epi effect on Isc. At 10(-5) M, YO increased by 70-fold the concentration of Epi required to produce a half-maximal effect (ED50; from 1.4 X 10(-7) M to 10(-5) M). YO and PZ by themselves had no significant effect on Isc in concentrations up to 10(-5) M. Clonidine, a specific alpha 2-agonist, decreased Isc with an ED50 similar to that of Epi; its effect was blocked by YO but not by PZ. Two alpha 1-selective agonists, methoxamine and phenylephrine, only caused a decrease in Isc in doses greater than 10(-5) M. This effect was reversed by YO but not by PZ. The effects of YO and PZ on Epi-modified Cl fluxes were also determined. YO completely aborted the effects of Epi on net Cl flux. No significant effects were seen with PZ. We conclude that the effects of Epi on ileal ion transport are mediated by a specific alpha 2-adrenergic receptor present in ileal mucosa and that no physiologic alpha 1-receptor function can be demonstrated.

scholarly journals P2Y receptors mediate Ca2+ signaling in duodenocytes and contribute to duodenal mucosal bicarbonate secretion

2009 ◽  
Vol 296 (2) ◽  
pp. G424-G432 ◽  
Author(s):  
Xiao Dong ◽  
Eric James Smoll ◽  
Kwang Hyun Ko ◽  
Jonathan Lee ◽  
Jimmy Yip Chow ◽  
...  
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
P2y Receptors ◽  
Epithelial Cell Line ◽  
Initial Increase ◽  
Bicarbonate Secretion ◽  
Duodenal Epithelium ◽  
And Function

Since little is known about the role of P2Y receptors (purinoceptors) in duodenal mucosal bicarbonate secretion (DMBS), we sought to investigate the expression and function of these receptors in duodenal epithelium. Expression of P2Y2 receptors was detected by RT-PCR in mouse duodenal epithelium and SCBN cells, a duodenal epithelial cell line. UTP, a P2Y2-receptor agonist, but not ADP (10 μM), significantly induced murine duodenal short-circuit current and DMBS in vitro; these responses were abolished by suramin (300 μM), a P2Y-receptor antagonist, or 2-aminoethoxydiphenyl borate (2-APB; 100 μM), a store-operated channel blocker. Mucosal or serosal addition of UTP induced a comparable DMBS in wild-type mice, but markedly impaired response occurred in P2Y2 knockout mice. Acid-stimulated DMBS in vivo was significantly inhibited by suramin (1 mM) or PPADS (30 μM). Both ATP and UTP, but not ADP (1 μM), raised cytoplasmic-free Ca2+ concentrations ([Ca2+]cyt) with similar potencies in SCBN cells. ATP-induced [Ca2+]cyt was attenuated by U-73122 (10 μM), La3+ (30 μM), or 2-APB (10 μM), but was not significantly affected by nifedipine (10 μM). UTP (1 μM) induced a [Ca2+]cyt transient in Ca2+-free solutions, and restoration of external Ca2+ (2 mM) raised [Ca2+]cyt due to capacitative Ca2+ entry. La3+ (30 μM), SK&F96365 (30 μM), and 2-APB (10 μM) inhibited UTP-induced Ca2+ entry by 92, 87, and 94%, respectively. Taken together, our results imply that activation of P2Y2 receptors enhances DMBS via elevation of [Ca2+]cyt that likely results from an initial increase in intracellular Ca2+ release followed by extracellular Ca2+ entry via store-operated channel.

Effect of serotonin on active electrolyte transport in rabbit ileum, gallbladder, and colon

1980 ◽  
Vol 239 (6) ◽  
pp. G463-G472 ◽  
Author(s):  
M. Donowitz ◽  
Y. H. Tai ◽  
N. Asarkof
Keyword(s):  
Maximum Concentration ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Electrolyte Transport ◽  
Rabbit Ileum ◽  
Rabbit Gallbladder ◽  
Epithelial Sheets ◽  
Dose Dependent ◽  
Stimulation Of

The effect of serotonin on active electrolyte transport was evaluated in vitro in epithelial sheets of rabbit ileum, gallbladder, and colon under short-circuited conditions. Serotonin added to the serosal surface of rabbit ileum caused a dose-dependent short-lived increase in short-circuit current and a more prolonged equal effect on net Na and Cl fluxes. The latter consisted primarily of inhibition of mucosal-to-serosal fluxes of both Na and Cl. In addition serosal serotonin decreased ileal Na influx from the mucosal solution into the epithelium, suggesting an effect on Na absorption. Serotonin did not alter all aspects of ileal absorptive function and did not affect glucose-dependent Na absorption. Consistent with serotonin acting by inhibiting NaCl absorption in the ileum, serotonin induced equal inhibition of net Na and Cl absorption in rabbit gallbladder (which has a linked Na and Cl absorptive process) but had no effect on rabbit colon (which lacks a linked Na and Cl absorptive process). In addition, adenosine 3',5'-cyclic monophosphate and serotonin both appeared to alter the same ileal NaCl absorptive process, since following stimulation of ileal secretion with the maximum concentration of theophylline, addition of serotonin did not cause any further effects.

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