Bicarbonate absorption by in vitro amphibian small intestine

1981 ◽  
Vol 241 (5) ◽  
pp. G389-G396 ◽  
Author(s):  
J. F. White ◽  
M. A. Imon
Keyword(s):  
Small Intestine ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Mucosal Surface ◽  
Electrical Potentials ◽  
The Media ◽  
Transepithelial Voltage ◽  
Ph Stat ◽  
Voltage Gradients

Isolated segments of jejunum from Amphiuma bathed in Cl--free (SO42(-)) media usually generated serosa-negative electrical potentials when HCO3(-) was present in the media. Bidirectional isotope fluxes under short circuit revealed a negligible absorption of Na+ and a residual flux consistent with anion absorption. Acetazolamide (10(-4) M) eliminated the short-circuit current and the residual flux. Segments of jejunum exposed on the mucosal surface to HCO3(-) (pH 7.4) alkalinized the unbuffered serosal fluid at a rate of about 1.1 mueq . h-1 . cm-2, as measured by the pH-stat while clamped at zero transepithelial potential. Acetazolamide, anoxia, and 2,4-dinitrophenol lowered the rate of alkalinization and simultaneously reduced the short-circuit current by an equal amount. Absorption was constant above a [HCO3(-)] of 35 meq/l and uninfluenced by applied transepithelial voltage gradients. HCO3(-) absorption was not reduced after replacement of media Na+ or Cl- but was reduced on addition of ouabain or removal of K+. It is concluded that the jejunum actively absorbs HCO3(-) by an electrogenic process that does not involve Na+-H+ exchange.

Association between HCO3(-) absorption and K+ uptake by Amphiuma jejunum: relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity

1984 ◽  
Vol 246 (6) ◽  
pp. G732-G744
Author(s):  
M. A. Imon ◽  
J. F. White
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Uptake Mechanism ◽  
Bathing Medium ◽  
The Media ◽  
Absorptive Flux ◽  
Free Media ◽  
Intracellular K Activity ◽  
K Activity

Titration techniques and K+- sensitive microelectrodes have been used to investigate the relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity in in vitro Amphiuma jejunum. The HCO3(-) absorptive flux (JHCO3(-] measured by pH-stat under short circuit was reduced by removal of K+ from the medium but not by replacement of Na+ with choline. JHCO3(-) exhibited a seasonal variation when K+ was absent from the media and was increased to a maximum when K+ equaled 5 mM. Addition of K+ to a K+-free luminal medium stimulated JHCO3(-) much more than addition to the serosal medium. Acetazolamide (10(-4) M) blocked K+-stimulated HCO3(-) absorption while benzolamide reduced the short-circuit current associated with HCO3(-) absorption much more rapidly when added to the mucosal bathing medium. Intracellular K+ activity (aik) and mucosal membrane potential (psi m) of jejunal villus cells were measured with double-barreled microelectrodes. When bathed bilaterally with HCO3(-)-containing media, K+ was actively accumulated for many hours (aik = 58.5 mM) but in the presence of ouabain fell to equilibrium (16 mM) after 2 h. In contrast, when HCO3(-) absorption was induced by removal of serosal HCO3(-), aik was elevated to 83.6 mM and, after 4-h exposure to ouabain cell K+, remained far above electrochemical equilibrium at 33 mM. Tissues bathed in Na+-free (Tris) media containing ouabain retained cell K+ after 4 h at even higher levels (46 mM). Cell K+ activity was reduced by removal of K+ from either the mucosal or serosal medium. Acetazolamide reduced aik over 2 h in Na+-free media from 66 to 42 mM. The decline in aik was associated with a concomitant decline in the HCO3(-) absorptive current. It is concluded that K+ is actively accumulated across both luminal and serosal membranes of the jejunal absorptive cell and that the luminal uptake mechanism is linked to HCO3(-) absorption or an equivalent process.

Receptors for vasoactive intestinal peptide and secretin on small intestinal epithelial cells

1980 ◽  
Vol 238 (3) ◽  
pp. G190-G196
Author(s):  
H. J. Binder ◽  
G. F. Lemp ◽  
J. D. Gardner
Keyword(s):  
Small Intestine ◽  
Guinea Pig ◽  
Vasoactive Intestinal Peptide ◽  
Binding Sites ◽  
Prostaglandin E1 ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Maximal Effect ◽  
Single Class

Binding of 125I-labeled vasoactive intestinal peptide (VIP) to dispersed enterocytes prepared from guinea pig small intestine was saturable, temperature dependent, and reversible, and reflected interaction of the labeled peptide with a single class of binding sites. Each enterocyte possessed approximately 60,000 binding sites and binding of the tracer to these sites could be inhibited by VIP [concentration for half-maximal effect (Kd), 12 nM] and by secretin (Kd greater than 1 micro M), but not by glucagon, gastrin, cholecystokinin, calcitonin, bombesin, litorin, physalaemin, substance P, eledoisin, serotonin, carbamylcholine, or histamine. With VIP and secretin, there was a close correlation between the relative potency for inhibition of binding of 125I-VIP and that for increasing cellular cAMP. For a given peptide, however, a 10-fold higher concentration was required for half-maximal inhibition of binding than for half-maximal stimulation of cellular cAMP. In addition to inhibiting binding of 125I-VIP and increasing cellular cAMP in enterocytes, secretin caused an increase in short-circuit current across guinea pig small intestine in vitro. Prostaglandin E1 increased cellular cAMP, but did not alter binding of 125I-VIP and the increase in cAMP caused by prostaglandin E1 plus VIP or secretin was equal to the sum of the increase caused by each agent alone.

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.

Sodium dependence of luminal alkalinization by rabbit ileal mucosa

1985 ◽  
Vol 249 (3) ◽  
pp. G358-G368 ◽  
Author(s):  
P. L. Smith ◽  
M. A. Cascairo ◽  
S. K. Sullivan
Keyword(s):  
Prostaglandin E1 ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Bathing Solution ◽  
Ileal Mucosa ◽  
Adrenergic Agents ◽  
Ussing Chambers ◽  
Sodium Removal ◽  
Ph Stat

Stripped rabbit ileal mucosa was studied in vitro in Ussing chambers under short-circuit conditions using the pH-stat technique to determine basal rates of luminal alkalinization; the contribution of the shunt pathway to the alkalinization process; the effects of Na, Cl, or HCO3 removal from the bathing solutions on luminal alkalinization; and the effects of epinephrine, ouabain, 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS), acetazolamide, prostaglandin E1 (PGE1), A23187, sugars, or amino acids on the alkalinization process. Results from these studies reveal that, under basal conditions, the rate of luminal alkalinization accounts for 81% of the basal short-circuit current (Isc), although there was no correlation between the rate of alkalinization and Isc. The contribution of the shunt to the alkalinization process accounts for less than 10% of the mucosal-to-serosal HCO3 flux. Removal of Cl from the bathing solutions increased the rate of luminal alkalinization and decreased Isc. Sodium removal from the bathing solutions reduced both Isc and the rate of luminal alkalinization. Addition of DIDS to the luminal or serosal bathing solution reduced luminal alkalinization less than 30%. Acetazolamide, PGE1, and A23187 were all without effect on luminal alkalinization. Addition of 3-O-methyl-D-glucose or L-alanine to the luminal bathing solution did not alter luminal alkalinization but increased Isc, D-Glucose added to the luminal bathing solution reduced luminal alkalinization. This effect appears to result from metabolic acid production since 1) it is not seen with L-alanine or 3-O-methyl-D-glucose; 2) in the absence of HCO3 in the bathing solutions, D-glucose increased luminal acidification; and 3) luminal addition of fructose also reduced the rate of luminal alkalinization. Addition of epinephrine to the serosal bathing solution stimulates a Na-dependent serosal alkalinization process. These results suggest that luminal alkalinization results from Na-dependent, transcellular HCO3 transport and that a Na-dependent, HCO3 absorptive process is stimulated by adrenergic agents.

Amiloride-sensitive salt and fluid absorption in small intestine of sodium-depleted rats

1985 ◽  
Vol 248 (1) ◽  
pp. G133-G141 ◽  
Author(s):  
P. C. Will ◽  
R. N. Cortright ◽  
R. G. Groseclose ◽  
U. Hopfer
Keyword(s):  
Small Intestine ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Proximal Colon ◽  
Salt Transport ◽  
Fluid Absorption ◽  
Major Pathway

Secondary hyperaldosteronism produced by Na+ depletion was associated with increases in salt and fluid absorption in both the small intestine and the distal colon but not in the cecum and the proximal colon. Because these changes had not been documented for the small intestine, this study focused on the regulation of this tissue. Increased NaCl and water absorption was expressed in vitro by increases in short-circuit current and transepithelial potential and in vivo by increased fluid absorption and a decreased luminal content of Na+ and water. For example, the short-circuit current in the ileum of Na+-depleted rats was 2-fold that of adrenalectomized and 1.3-fold that of adrenal-intact control animals. The short-circuit current was inhibitable 24 +/- 14% by micromolar concentrations of amiloride in Na+-deficient animals compared with 1 +/- 3% in control animals. Similarly, ileal fluid absorption in vivo was 2.3-fold higher in Na+-deficient relative to control animals. The additional fluid absorption was sensitive to 50 microM amiloride, whereas amiloride had no effect in control animals. Furthermore, the Na+ content of the chyme from the ileum of Na+-deficient animals was about half that of controls. These results suggest that mineralocorticoids can induce the amiloride-sensitive Na+ transporter in the small intestine and that this type of epithelial salt transport can become a major pathway for salt retention by the small intestine.

Adrenergic agents stimulate and cholinergic agents inhibit H+ secretion by amphibian jejunum

1986 ◽  
Vol 251 (3) ◽  
pp. G405-G412
Author(s):  
J. F. White ◽  
R. Britanisky
Keyword(s):  
Acid Secretion ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Atpase Inhibitor ◽  
Adrenergic Agents ◽  
Cholinergic Agents ◽  
Ph Stat ◽  
Opposing Effects ◽  
Dose Dependent Increase

In vitro segments of Amphiuma jejunum secrete H+ spontaneously. This study explored the effect of cholinergic and adrenergic agents on H+ secretion. Segments of mucosa were short-circuited and exposed on their mucosal surface to HCO3- -buffered medium while the pH of the unbuffered serosal medium was held by the pH-stat technique. Methacholine added to the serosal medium nearly abolished the spontaneous short-circuit current (Isc) and serosal alkalinization (JHCO3-) with an EC50 of 3.7 X 10(-7) M. Subsequent addition of norepinephrine (NE) to the serosal medium caused a dose-dependent increase in Isc and JHCO3. For three catecholamines the order of potency was epinephrine greater than NE greater than isoproterenol. The spontaneous Isc was significantly reduced (P less than 0.05) by the gastric H+-K+-ATPase inhibitor omeprazole, while the NE-induced Isc was unaltered by the inhibitor. Replacement of medium Na+ with choline abolished the response to NE. The NE-induced Isc was also reduced by methacholine. Acetazolamide inhibited the spontaneous and NE-induced Isc and JHCO3. In summary, cholinergic and adrenergic agents have opposing effects on intestinal H+-HCO3- transport. Jejunal acid secretion may be controlled in part by these antagonistic influences. Adrenergically activated acid secretion occurs by a different mechanism than spontaneous acid secretion.

Norepinephrine induces Na+-H+ and Cl -HCO3 exchange in Amphiuma intestine: locus and response to amiloride

1988 ◽  
Vol 255 (1) ◽  
pp. G18-G26
Author(s):  
J. F. White ◽  
C. F. Hinton
Keyword(s):  
Small Intestine ◽  
Acid Secretion ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Induced Current ◽  
Free Medium ◽  
Cl Transport ◽  
Transepithelial Voltage ◽  
Unidirectional Fluxes ◽  
Stimulation Of

Catecholamines stimulate Na+-dependent acid secretion by Amphiuma small intestine. Studies were undertaken to localize the response within the mucosa and characterize the effect on Na+ and Cl- transport. Stripped segments of jejunum were mounted in tissue chambers that permitted isolation of villus or intervillus epithelium. In Cl-free medium, norepinephrine (NE) stimulated the transepithelial voltage (Vms) in both villus and intervillus epithelium, whereas galactose and valine elevated Vms predominately in the villus. Paired segments of whole mucosa were maintained under short circuit while the rate of acid secretion (JH) was measured by titration of the unbuffered serosal medium and unidirectional fluxes of Na+ were measured by 22Na. NE significantly stimulated net Na+ absorption (JNanet), short circuit current (Isc), and JH. Amiloride reduced JH and Isc in NE-stimulated tissues and blocked the stimulation of JNanet by NE. The NE-induced current was nearly completely and reversibly inhibited by replacement of luminal medium HCO3- or CO2. NE significantly stimulated net Cl- absorption without changing Isc or JH. It is concluded that cells throughout the mucosa respond to catecholamines with enhanced Na+ and Cl- absorption, possibly through induction or stimulation of Na+-H+ and Cl- -HCO3- exchange.

OSMOTIC INHIBITION OF THE NATRIFERIC RESPONSE OF THE TOAD URINARY BLADDER TO VASOPRESSIN

1975 ◽  
Vol 67 (1) ◽  
pp. 119-125
Author(s):  
P. J. BENTLEY
Keyword(s):  
Urinary Bladder ◽  
Water Movement ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Toad Bladder ◽  
Toad Urinary Bladder ◽  
Electrical Potential Difference ◽  
Osmotic Gradient

SUMMARY The electrical potential difference and short-circuit current (scc, reflecting active transmural sodium transport) across the toad urinary bladder in vitro was unaffected by the presence of hypo-osmotic solutions bathing the mucosal (urinary) surface, providing that the transmural flow of water was small. Vasopressin increased the scc across the toad bladder (the natriferic response), but this stimulation was considerably reduced in the presence of a hypo-osmotic solution on the mucosal side, conditions under which water transfer across the membrane was also increased. This inhibition of the natriferic response did not depend on the direction of the water movement, for if the osmotic gradient was the opposite way to that which normally occurs, the response to vasopressin was still reduced. The natriferic response to cyclic AMP was also inhibited in the presence of an osmotic gradient. Aldosterone increased the scc and Na+ transport across the toad bladder but this response was not changed when an osmotic gradient was present. The physiological implications of these observations and the possible mechanisms involved are discussed.

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.

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