Effects of lactose on calcium absorption and secretion by rat ileum

1984 ◽  
Vol 246 (3) ◽  
pp. G281-G285 ◽  
Author(s):  
M. J. Favus ◽  
E. Angeid-Backman
Keyword(s):  
Calcium Absorption ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Direct Effects ◽  
Dihydroxyvitamin D3 ◽  
Rat Ileum ◽  
Tissue Polarity ◽  
Net Flux ◽  
Absorptive Flux

The direct effects of lactose on net intestinal calcium absorption were determined by measuring unidirectional steady-state calcium fluxes in vitro under short-circuited conditions in segments of rat ileum. The isosmotic mucosal additions in segments of rat ileum. The isosmotic mucosal addition of lactose (160 mM) increased net calcium absorption (J net) by increasing the absorptive flux from mucosa to serosa (Jm----s) and reducing the secretory flux from serosa to mucosa (Js----m). Lactose also reduced tissue conductance and short-circuit current and reversed tissue polarity. 1,25-Dihydroxyvitamin D3 administration (50 ng/day for 4 days) increased J net from secretion to no net flux (Jm----s = Js----m), and lactose increased J net further to net absorption. Removal of sodium from the medium, like lactose addition, increased J net by increasing Jm----s and reducing Js----m. The replacement of medium sodium with choline abolished a further increase of J net by lactose. These results show that lactose increases net calcium absorption in the absence of transepithelial electrochemical or osmotic gradients. Transcellular calcium transport may be stimulated by lactose by hyperpolarization of the brush border as a result of reduced mucosal sodium.

Effects of somatostatin on intestinal calcium transport in the rat

1981 ◽  
Vol 241 (3) ◽  
pp. G215-G221
Author(s):  
M. J. Favus ◽  
M. Berelowitz ◽  
F. L. Coe
Keyword(s):  
Tissue Concentration ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Strongly Correlated ◽  
Dihydroxyvitamin D3 ◽  
Intestinal Segments ◽  
Absorptive Flux ◽  
Calcium Secretion ◽  
Stimulation Of

The addition of somatostatin (SRIF) to rat descending colon in vitro increased the calcium secretory flux from serosa to mucosa (Js leads to m) and reduced tissue short-circuit current (Isc) but did not alter the absorptive flux from mucosa to serosa (Js leads to m). Js leads to m increased by 37% at 10(-9) M SRIF and by 48% at 10(-6) M. The response to SRIF was not altered by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and SRIF did not interfere with stimulation of calcium Jm leads to s by 1,25(OH)2D3. Removal of sodium from the buffer abolished the stimulation of Js leads to m by SRIF without reducing basal Js leads to m. Secretory fluxes of mannitol and calcium were strongly correlated in the presence and absence of SRIF, suggesting that SRIF stimulates a paracellular transepithelial pathway for calcium. In the duodenum, SRIF altered neither calcium Js leads to m nor Isc. In the ileum, calcium Js leads to m increased and Isc decreased, as in the colon, but only by 28 and 12%, respectively. The maximal change in calcium Js leads to m caused by SRIF in these three intestinal segments was negatively correlated with the tissue concentration of immunoreactive SRIF. These results suggest that intestinal calcium secretion could, in part, be regulated by intestinal SRIF.

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.

Ca fluxes across duodenum and colon of spontaneously hypertensive rats: effect of 1,25(OH)2D3

1986 ◽  
Vol 251 (2) ◽  
pp. F278-F282 ◽  
Author(s):  
U. Gafter ◽  
S. Kathpalia ◽  
D. Zikos ◽  
K. Lau
Keyword(s):  
Calcium Transport ◽  
Spontaneously Hypertensive Rats ◽  
Calcium Absorption ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Calcium Flux ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Wistar Kyoto

Calcium absorption by spontaneously hypertensive rats (SHR) was variably reported to be different from normotensive Wistar-Kyoto (WKY) controls. Furthermore, blunted responsiveness to the intestinal effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has also been postulated. To evaluate this hypothesis, calcium fluxes were measured by the Ussing technique across duodenum and descending colon with or without prior 1,25(OH)2D3 treatment. Duodenal mucosal-to-serosal calcium flux (Jm----s) (44.9 vs. 52.4 nmol X cm-2 X h-1), serosal-to-mucosal flux (Js----m) (25.6 vs. 28.4 nmol X cm-2 X h-1), and net flux (Jnet) were comparable. 1,25(OH)2D3 increased duodenal Jm----s in both SHR and WKY groups (95.2 and 86.8 nmol X cm-2 X h-1). Js----m was lower in SHR (26.1 vs. 35.6 nmol X cm-2 X h-1, P less than 0.01), although the tendency for a higher Jnet in SHR (68.6 vs. 51.2 nmoles X cm-2 X h-1) was statistically insignificant. Short-circuit current was higher in the colon of SHR, both before and after 1,25(OH)2D3, suggesting increased sodium transport. Basal colonic Jnet was virtually zero in both groups but comparably increased by 1,25(OH)2D3 because of stimulation in only Jm----s. Prevention of hypertension by hydralazine since the 4th wk of age did not alter the findings compared with the hypertensive SHR, suggesting calcium transport rates were unaffected by hypertension. These data indicate that in vitro, duodenal, and colonic active calcium transport by the SHR is similar to WKY. Their normal responses to 1,25(OH)2D3 do not support the hypothesis of intestinal resistance.

Regulation of Na-Cl absorption in rabbit proximal colon in vitro

1987 ◽  
Vol 252 (1) ◽  
pp. G45-G51 ◽  
Author(s):  
J. H. Sellin ◽  
R. De Soignie
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Beta Agonist ◽  
Disulfonic Acid ◽  
Low Concentrations ◽  
Cotransport System ◽  
Net Flux

Ion transport in rabbit proximal colon (PC) in vitro is dominated by a Na-Cl cotransport system stimulated by epinephrine. To further characterize the regulation of Na-Cl transport, we tested the effects of specific adrenergic agonists on ion fluxes under short-circuit conditions. Additionally, we tested the effects of the transport inhibitors bumetanide, furosemide, and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). Basal Na and Cl absorption were essentially nil [Na net flux (JNanet) = 0.3 +/- 0.4, and Cl net flux (JClnet) = -0.5 +/- 0.5 mu eq X cm-2 X h-1, means +/- SE]. The alpha 2-agonist clonidine significantly increased net Na and Cl absorption (delta JNanet = 3.0 +/- 0.6 mu eq X cm-2 X h-1, delta JClnet = 2.0 +/- 0.4 mu eq X cm-2 X h-1) with a minimal change in short-circuit current (delta Isc = 0.1 +/- 0.1 mu eq X cm-2 X h-1). The alpha 1-agonist phenylephrine and the beta-agonist isoproterenol did not alter ion transport. The alpha 2-blocker yohimbine (YOH) had a complex, concentration-dependent effect. At low concentrations (10(-6)-10(-8) M) YOH effectively inhibited epinephrine-stimulated cotransport. Compared with 10(-8)M YOH, 10(-6) YOH blocked 90% of the epinephrine-induced increases in Na and Cl absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 1,25(OH)2D3 and calcium channel blockers on cecal calcium transport in the rat

1985 ◽  
Vol 248 (6) ◽  
pp. G676-G681 ◽  
Author(s):  
M. J. Favus ◽  
E. Angeid-Backman
Keyword(s):  
Vitamin D ◽  
Calcium Channel ◽  
Calcium Transport ◽  
Calcium Absorption ◽  
Channel Blockers ◽  
Dihydroxyvitamin D3 ◽  
High Concentrations ◽  
Absorptive Flux ◽  
Mucosal Side

To determine whether calcium transport across rat cecum is vitamin D dependent, we measured in vitro bidirectional calcium fluxes under short-circuited conditions across cecum from rats that were vitamin D deficient, vitamin D replete, or vitamin D deficient or vitamin D replete and injected with either 10, 25, or 75 ng of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] daily for 4 days before study. Vitamin D deficiency decreased net calcium absorption (Jnet) by reducing the mucosal-to-serosal absorptive flux (Jm----s) from 168 +/- 18 to 33 +/- 5 nmol X cm-2 X h-1 (mean +/- SE, P less than 0.0001). Twenty-five nanograms of 1,25(OH)2D3 raised Jm----s to 124 +/- 17 nmol X cm-2 X h-1, not different from values in vitamin D-replete rats. Although active calcium absorption by cecum appears to respond to vitamin D, calcium Jm----s is near maximal under normal conditions, and further stimulation follows only pharmacological doses of 1,25(OH)2D3. The in vitro addition of the calcium channel blocker verapamil (5 X 10(-5) M) to the mucosal side of cecum from vitamin D-replete rats reduced calcium Jm----s, but lower concentrations of verapamil or nitrendipine (10(-5) to 10(-9) M) did not reduce calcium Jm----s. The lack of inhibition by low concentrations of channel blockers suggest that the plasma membrane channels for calcium translocation across intestinal epithelium may not be analogous to voltage-dependent calcium channels in excitable tissue. The inhibition of cecal calcium transport that was blocked by high concentrations of verapamil may represent a nonspecific effect of the agent.

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.

Kinetic characteristics of calcium absorption and secretion by rat colon

1981 ◽  
Vol 240 (5) ◽  
pp. G350-G354 ◽  
Author(s):  
M. J. Favus ◽  
S. C. Kathpalia ◽  
F. L. Coe
Keyword(s):  
Active Transport ◽  
Calcium Absorption ◽  
Rat Colon ◽  
Kinetic Characteristics ◽  
Bathing Medium ◽  
Dihydroxyvitamin D3 ◽  
Extracellular Flux ◽  
Descending Colon ◽  
Absorptive Flux

The kinetic characteristics of calcium active transport in rat descending colon were determined by measuring unidirectional transmural calcium fluxes in vitro. The absorptive flux from mucosa to serosa (Jm leads to s) was saturable, with a calculated affinity (Kt) of calcium for the transport system of 1.6 mM and a maximal transport capacity (Vmax) of 133 nmol.cm-2.h-1. The administration of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] increased Jm leads to s by increasing Vmax to 236 nmol.cm-2.h-1 without changing Kt (1.8 mM). The secretory flux from serosa to mucosa (Js leads to m) was not saturable and was not increased by 1,25(OH)2D3. Mannitol, a marker of transepithelial extracellular flux, underwent net absorption in the absence of electrochemical gradients, and its Jm leads to s and Js leads to m were not altered by 1,25(OH)2D3 administration. Addition of 11 mM D-glucose to the bathing medium consistently increased calcium Js leads to m and mannitol Jm leads to s and Js leads to m. Glucose reduced net calcium absorption except when sodium was removed from the medium. Calcium Js leads to m varied linearly with mannitol Js leads to m over the range of medium calcium from 0.125 to 5.0 mM. The behavior of calcium absorption by descending colon is compatible with a carrier-mediated, active-transport mechanism, whereas calcium secretion occurs by a nonsaturable process via a predominately paracellular pathway.

Hormonal control of chloride transport across locust rectum

1978 ◽  
Vol 56 (8) ◽  
pp. 1879-1882 ◽  
Author(s):  
J. Spring ◽  
J. Hanrahan ◽  
J. Phillips
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Fold Increase ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Hormonal Control ◽  
Net Flux ◽  
Hemolymph Volume ◽  
Camp Levels

Rates of ion transport across locust recta were monitored in vitro by following fluxes of 22Na+ and 36Cl−, short-circuit current (Isc), and open-circuit electropotential difference (PD) across this epithelium for several hours. Corpora cardiaca (CC) homogenates, cAMP, theophylline, and hemolymph of recently fed locusts all stimulate electrogenic transport of Cl− across locust rectum, as indicated by a two- to three-fold increase in 36Cl− net flux, Isc, and PD. Cyclic AMP caused a Cl-dependent increase in PD across the lumen-facing but not the hemocoel-facing plasma membrane of the epithelial cells. We propose that a blood-borne factor, possibly from the CC, causes an elevation in cAMP levels in rectal tissue and that this second messenger acts by increasing Cl− entry into the cell from the rectal lumen. Additional fluid absorption accompanies the resulting increase in transport of NaCl, leading to an increase in the hemolymph volume of previously dehydrated locusts.

Antisecretory effects of berberine in rat ileum

1981 ◽  
Vol 241 (3) ◽  
pp. G253-G258 ◽  
Author(s):  
Y. H. Tai ◽  
J. F. Feser ◽  
W. G. Marnane ◽  
J. F. Desjeux
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Rat Ileum ◽  
Ion Secretion ◽  
Stimulation Of

The in vitro antisecretory effects of the alkaloid berberine (1.0 mM) on intestinal ion secretion and mucosal adenylate cyclase and Na-K-ATPase activities were studied in the rat ileum. Mucosal berberine did not alter the individual basal net ion fluxes and basal adenylate cyclase activity but decreased short-circuit current (Isc) and increased the net absorption of chloride plus bicarbonate. In the cholera toxin-treated tissue, mucosal berberine stimulated absorption of Na and Cl and inhibited the increased adenylate cyclase activity but did not change the specific Na-K-ATPase activity, whereas serosal berberine stimulated Na secretion and decreased Isc. Mucosal berberine also decreased Isc, increased Cl permeability, and reversed the ion secretion induced by dibutyryl cyclic AMP, the heat-stable enterotoxin of Escherichia coli, and methylprednisolone administration. The antisecretory effects of mucosal berberine may be explained by stimulation of a Na-Cl-coupled absorptive transport process. The mechanism of action of serosal berberine remains to be elucidated. However, it is clear that mucosal berberine affects intestinal ion transport by mechanisms different from stimulation of the Na pump and probably at a step distal to the production or degradation of cyclic AMP or cyclic GMP.

Effect of ethanol on ion transport and electrical properties of dog trachea in vitro

1983 ◽  
Vol 54 (5) ◽  
pp. 1335-1339 ◽  
Author(s):  
F. D. McCool ◽  
J. P. Zorn ◽  
M. G. Marin
Keyword(s):  
Electrical Properties ◽  
Ion Transport ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Tracheal Epithelium ◽  
Electrical Potential Difference ◽  
Net Flux ◽  
Circuit Technique

We studied the effect of ethanol on the electrical and ion transport properties of dog tracheal epithelium using Ussing's short-circuit technique. There was a significant reduction of short-circuit current and electrical potential difference and a tendency of electrical resistance to increase in response to increasing concentrations of ethanol in the bathing solutions. Threshold changes in the electrical properties were noted at an ethanol concentration of 3.3 microliter/ml (260 mg/100 ml). Ethanol did not produce these changes in electrical properties when Cl- and Na+ were substituted in the bathing media with either choline or SO2-(4). In five paired tissue preparations, ethanol (13.3 microliters/ml) significantly reduced the net flux of Cl- toward the lumen from 2.68 +/- 0.62 to 1.00 +/- 0.69 (SE) mu eq X cm-2 X h-1, due primarily to a reduced unidirectional flux of Cl- from submucosa to lumen. These observations demonstrate that ethanol has an effect on the ion transport and electrical properties of dog tracheal epithelium at concentrations that may be of clinical relevance.

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