Biomedical subjects

W Rummel

Publications and source records attributed to W Rummel.

At least 37 records · Page 2Linked to original sources

PubMed1990

Cellular and paracellular magnesium transport across the terminal ileum of the rat and its interaction with the calcium transport.

Concentration and voltage dependence of unidirectional magnesium fluxes across the stripped mucosa of the rat terminal ileum were measured in an Ussing chamber. The mucosa-to-serosa magnesium flux exhibited a curvilinear concentration dependence, whereas serosa-to-mucosa flux of magnesium was linearly related to magnesium concentration between 0.25 and 5 mM. At low concentrations magnesium was absorbed, whereas at the magnesium concentration of 5 mM the serosa-to-mucosa magnesium flux was higher than the mucosa-to-serosa flux, resulting in magnesium secretion. Only the mucosa-to-serosa flux of magnesium had a voltage-independent (i.e., nondiffusive) cellular component. Due to the high capacity of this cellular mucosa-to-serosa transport of magnesium, which was about 7.5 times greater than that of calcium, absorption of magnesium was performed in the terminal ileum in contrast to calcium, which was secreted under the same conditions. However, magnesium serosa-to-mucosa flux was totally voltage dependent (i.e., diffusive) and probably restricted to the paracellular pathway. The diffusive serosa-to-mucosa flux of magnesium was about two times greater than the diffusive fraction of the mucosa-to-serosa transport of magnesium. The prevalence of the diffusive serosa-to-mucosa flux of magnesium over that from mucosa to serosa, responsible for magnesium secretion observed at the magnesium concentration of 5 mM, may be explained by an "anomalous solvent drag effect." Voltage clamp experiments showed that magnesium had no effect on the cellular mucosa-to-serosa transport of calcium. However, it decreased the diffusive calcium flux in this direction. 1 alpha,25-dihydroxyvitamin D3 did not influence the unidirectional or net magnesium transport but increased the calcium flux in both directions to the same degree. In conclusion, magnesium is absorbed in the terminal ileum at least partially by a cellular, vitamin D3-insensitive process that is different from the calcium transport mechanism.

Animals↗

PubMed1990

Arachidonic acid-induced secretion in the rat colon. Indomethacin-resistant neuronal and epithelial actions.

The effect of arachidonic acid on short-circuit current (Isc) was studied in two preparations of the rat colon descendens, one with and one without the submucosal plexus. In both preparations, arachidonic acid (10(-7)-5 x 10(-5) mol.l-1) increased Isc concentration-dependently. The cyclooxygenase blocker, indomethacin, inhibited its action only partially. The lipoxygenase inhibitor, nordihydroguaiaretic acid, was an ineffective inhibitor of the response to arachidonic acid. Tetrodotoxin (TTX), atropine, and hexamethonium blocked the effect of arachidonic acid in the preparation with the submucosal plexus. Inhibition by neuronal blockers was also observed in the presence of indomethacin. After removal of the submucosal plexus, TTX no longer affected the Isc response evoked by arachidonic acid. This epithelial action of arachidonic acid was inhibited by the calmodulin antagonist, trifluoperazine, and the intra-cellular Ca2(+)-antagonist, TMB-8. Inhibition by these drugs was also found in the presence of indomethacin. Consequently, for the secretion induced by arachidonic acid two sites of action, the submucosal plexus and the epithelium, and two mechanisms of action, prostaglandin-mediated and non-mediated, could be distinguished.

Animals↗

PubMed1989

Cholinergic-mediated secretion in the rat colon: neuronal and epithelial muscarinic responses.

The acetylcholine receptor agonists, acetylcholine (10(-5)-10(-4 M), carbachol (5 x 10(-6)-5 x 10(-5) M), bethanechol (5 x 10(-5)-5 x 10(-4) M) and dimethylphenylpiperazinium (DMPP, 10(-5) M) increased the short-circuit current (Isc) in the rat colon descendens by a tetrodotoxin (TTX)-sensitive mechanism. Blockade by TTX was still observed after removal of the submucosa, indicating the involvement of neurons of the mucosal plexus. Hexamethonium (10(-5) M) and atropine (10(-6) M) were used to distinguish between nicotinic and muscarinic neuronally mediated effects. The inhibitor of choline uptake, hemicholinium-3 (1 mM), reversibly inhibited the effect of repeated electric field stimulation (EFS). The EFS response was only inhibited by high concentrations of atropine (greater than or equal to 10(-5) M). In mucosa-submucosa preparations 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) was more effective than telenzepine whereas pirenzepine was ineffective. Pirenzepine inhibited the EFS response in mucosa preparations as did telenzepine and 4-DAMP. It was not possible to differentiate between the muscarinic receptors involved in the different parts of the enteric nervous system on the basis of our results.

Acetylcholine↗

PubMed1989

Single chloride channels in colon mucosa and isolated colonic enterocytes of the rat.

Chloride channels from rat colonic enterocytes were studied using the patch-clamp technique. After removal of mucus, inside-out patches were excised from the apical membrane of intact epithelium located at the luminal surface. They contained spontaneously switching Cl- channels with a conductance of 35-40 pS. The channels were blocked reversibly by anthracene-9-carboxylic acid (1mM). In excised patches from single enterocytes, isolated by calcium removal, the Cl- channels were studied in more detail. The I-V relation was linear between +/- 80 mV. The selectivity was I- greater than Br- greater than Cl- = NO3- greater than F- = HCO3-. Thirty pS Cl- channels were also found on the basolateral membrane of crypts isolated by brief calcium removal. The I-V curve of these Cl- channels was also linear. The results provide direct evidence for the existence of Cl- channels in the apical membrane of surface cells in colonic mucosa. The properties of these channels are similar to those previously observed when incorporating membrane vesicles into planar lipid bilayers. Both results support the validity of the theoretical models describing intestinal secretion.

Animals↗

PubMed1989

Antisecretory effects of somatostatin and vasopressin in the rat colon descendens in vitro.

The effects of two hormones, vasopressin and somatostatin (SOM), on ion secretion in rat colon descendens were compared. Three modes for induction of epithelial secretion were used: neuronally mediated secretion due to electric field stimulation (EFS), Ca2+-dependent secretion elicited by carbachol, and cAMP-dependent secretion evoked either by a receptor-mediated mechanism elicited by vasoactive intestinal peptide (VIP) or by a direct activation of the adenylate cyclase by means of forskolin. Somatostatin inhibited ion secretion evoked by EFS (55-65%), carbachol (80%) and VIP (95%) in a dose-dependent manner. Maximal inhibition by SOM was observed at 10(-7) M. Somatostatin had, however, no effect on the secretory response to forskolin. The inhibition of the VIP effect could be attenuated by pretreatment with pertussis toxin. In contrast, vasopressin in concentrations as low as 0.025-0.25 U/liter decreased the secretory effects of EFS (55-75%) and carbachol (85%), but had no effect on cAMP-dependent secretion elicited either by VIP or forskolin. The results suggest that the antisecretory effect of vasopressin is mediated only by a block in the Ca2+ pathway, whereas SOM inhibits Ca2+-dependent secretion as well as receptor-mediated cAMP-dependent secretion. The interaction with the cAMP pathway is located at the step between stimulation of the receptor and activation of the adenylate cyclase and probably involves an Ni-protein.

Animals↗

PubMed1989

Actions of the Cl- channel blocker NPPB on absorptive and secretory transport processes of Na+ and Cl- in rat descending colon.

The effects of the Cl- channel blocker, NPPB (5-nitro-2-(3-phenylpropylamino)-benzoate), on the transport of Na+ and Cl- in the descending colon of the rat were studied in the Ussing chamber. In control tissue, NPPB administered at the mucosal side of the epithelium increased the short-circuit current (Isc) and inhibited the unidirectional mucosa-to-serosa fluxes of Na+ and Cl-. In HCO3- - or Cl- -free media for in the presence of SITS (4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulphonic acid), this increase in Isc caused by mucosal NPPB was not observed. The serosal administration of NPPB was without effect. Mucosal NPPB (10(-4) mol l-1) decreased the forskolin-induced increase in Isc by only about 60%. However, the activation of the serosa-to-mucosa flux of Cl- caused by forskolin was inhibited completely. NPPB decreased the mucosa-to-serosa fluxes of Na+ and Cl- reduced additionally by forskolin. Serosal NPPB decreased Isc and FNasm, but had no effect on FNams or FClmas. In HCO3- -free buffer the increase in Isc induced by forskolin was inhibited completely by NPPB. The inhibition of Cl- secretion by NPPB fits well with the capacity of the drug to block Cl- channels. For the inhibition of neutral NaCl absorption two sites of action are discussed: an interaction with the Cl-/HCO3- exchanger or an interference with the extrusion of Cl- through the basolateral membrane.

Animals↗

PubMed1988

Action of loperamide on neuronally mediated and Ca2+- or cAMP-mediated secretion in rat colon.

The action of loperamide on the ion secretion evoked in rat colon descendens by electric field stimulation of enteric neurons, on the Ca2+-dependent secretion due to carbachol, and on the cAMP-mediated secretion elicited by forskolin was studied. Loperamide blocked all three types of secretion, but about 10 times higher concentrations of the drug were necessary to block the secretion caused by forskolin than to block the secretion mediated neuronally or by Ca2+. All the effects of loperamide were mimicked by trifluoperazine, a calmodulin antagonist. Neither morphine nor the Ca2+ channel blocker, verapamil, mimicked the effects of loperamide on ion transport. Therefore it seems reasonable to conclude that the antisecretory action of loperamide in the rat colon is caused by a block of the calmodulin system.

Animals↗

PubMed1988

Indirect effects of bradykinin on ion transport in rat colon descendens: mediated by prostaglandins and enteric neurons.

The effect of bradykinin on two preparations of rat colon descendens was examined. In a mucosa-submucosa preparation consisting of the submucosal plexus, the mucosal plexus and the epithelium bradykinin (10(-10)-5 X 10(-9) mol.l-1) caused an increase in Isc, Gt and Pd which was to more than 70% diminished by TTX. However, in a mucosa preparation consisting of only the mucosal plexus and the epithelium bradykinin caused an increase in Isc, Gt and Pd, which was not affected by TTX. Ten times higher concentrations of bradykinin were needed in the mucosa preparation to reach the same effects as in the mucosa-submucosa preparation. All effects of bradykinin were markedly reduced in the presence of indomethacin indicating that they were mediated by prostaglandins in both preparations. The bradykinin effect in the mucosa-submucosa preparation but not in the mucosa preparation was reduced about 50% by atropine. The results suggest that bradykinin activates prostaglandin synthesis. Prostaglandins subsequently stimulate neurons in the submucosal plexus which induce a secretory response on the epithelium partially mediated by a muscarinic receptor. In a high concentration bradykinin due to the induction of prostaglandin synthesis can also activate directly the mucosal epithelium.

Animals↗

PubMed1988

Neuronally mediated and direct effects of prostaglandins on ion transport in rat colon descendens.

Two preparations of rat colon descendens were used in order to localize the action sites of iloprost and prostaglandin E2 (PGE2). One preparation, the mucosa-submucosa preparation contained the submucosal and mucosal plexus whereas for the mucosa preparation in addition the submucosa with the submucosal plexus was removed. Iloprost (10(-6) mol.l-1) caused an increase in short-circuit current (Isc), potential difference (Pd) and tissue conductance (Gt) of the mucosa-submucosa preparation reflecting net Cl- secretion as confirmed by unidirectional ion flux measurements. The Cl- secretion was due to an increase in JClsm and a decrease in JClms. These effects were completely abolished by addition of 5 X 10(-5) mol.l-1 atropine. Iloprost had only small and inconsistent effects in the mucosa preparation. In contrast PGE2 (10(-6) mol.l-1) increased Isc, Pd and Gt due to Cl- secretion in both preparations. The Cl- secretion was caused by an increase in JClsm and a decrease in JClms. Only the PGE2 effect in the mucosa-submucosa preparation but not in the mucosa preparation was inhibited by about 50% by atropine. The results suggest that the prostacyclin derivative iloprost induces a Cl- secretion only by an activation of submucosal neurons whereas PGE2 acts both on the epithelium and the submucosal plexus. The neuronal effects of prostaglandins appear to be, at least in part, mediated by muscarinic receptors.

Animals↗

PubMed1988

Na+ uptake into colonic enterocyte membrane vesicles.

Na+ uptake was studied in colonic enterocyte membrane vesicles prepared from normal and dexamethasone-treated rats. Vesicles from rats treated with dexamethasone demonstrated a fivefold greater 22Na+ uptake compared with vesicles from normal rats. Most of the tracer uptake in membranes derived from treated rats occurred through a conductive, amiloride-blockable pathway located in vesicles with low native K+ permeability and high Cl- permeability. Kinetic analysis of the amiloride inhibition curve revealed the presence of two amiloride-blockable pathways, one with a high affinity (Ki = 9 +/- 1.8 nM), accounting for 85% of the uptake, and one with a low affinity (Ki = 2.2 +/- 0.71 microM), accounting for only 12% of the uptake. Only the low-affinity pathway was detected with vesicles from normal rats. The high sensitivity to amiloride, the dependence on dexamethasone pretreatment, and the relative permeabilities to K+ and Cl- indicate that most of the 22Na+ uptake in membranes derived from treated rats is through a Na+-specific channel located in apical membrane vesicles. Preincubation of the isolated cells from dexamethasone-treated rats at 37 degrees C in Ca2+-free solutions before homogenization and membrane vesicle purification caused a 5- to 10-fold increase in amiloride-blockable 22Na+ uptake compared with vesicles derived from cells maintained at 0 degrees C. The addition of Ca2+, but not of Mg2+, to the incubation solution markedly reduced this temperature-dependent enhancement in 22Na+ uptake. The uptake of 22Na+ into vesicles from normal rats was unaffected by preincubation at 37 degrees C or the addition of Ca+ to the incubation solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗

PubMed1987

Strontium transport in the rat colon.

Concentration dependence of strontium (Sr) fluxes across the colon ascendens and descendens of the rat were measured in a modified Ussing-chamber. Mucosa (m) to serosa (s) and s to m Sr fluxes across both colonic segments were linearly related to the Sr concentration from 0.125 mmol/l to 10 mmol/l. In the colon ascendens m to s Sr fluxes were slightly higher than the fluxes in the opposite direction, resulting in net Sr absorption. In the colon descendens s to m fluxes were higher than the ms fluxes, resulting in net Sr secretion. Neither Sr nor calcium (Ca) showed a concentration dependent interaction with respect to their unidirectional fluxes in both parts of the colon. Only in the colon ascendens Sr at the highest concentration (10 mmol/l) inhibited m to s calcium transport. Experiments, in which the voltage dependence of the unidirectional Sr fluxes was measured confirmed the results obtained from the concentration dependence: The unidirectional fluxes of Sr across the colon ascendens and descendens were totally voltage dependent, i.e. diffusive. In the colon descendens the voltage dependence of the s to m flux was steeper than the flux from m to s. It is hypothesized that this prevalence is caused by an anomalous solvent drag effect. 1.25-Dihydroxyvitamin D3 [1.25 (OH)2D3] stimulated m to s calcium flux in the colon descendens but had no effect on Sr flux. The results demonstrate that Sr and Ca in the rat colon are transported by different mechanisms. In contrast to the Ca transport the Sr flux is only diffusive and insensitive to 1.25 (OH)2D3.

Action Potentials↗

PubMed1987

Dependence of intestinal iron absorption on the valency state of iron.

1. In rats iron was absorbed after administration into the gut lumen as ferric iron bound to serum albumin, to nitrilotriacetic acid, and to 8-OH-quinoline sulfonic acid, or as isolated diferri-transferrin. 2. Iron absorption from 59Fe-labelled transferrin was inhibited by the addition of rat plasma. 3. The inhibitory component in the rat plasma turned out to be ceruloplasmin (ferrous iron oxidase, EC 1.16.2.1). 4. The absorption of iron from these ferric iron complexes was also inhibited by addition to the incubation medium of ferrozine, a strong anionic Fe(II)-ligand. 5. Uptake and absorptive utilization of transferrin-bound ferric iron was decreased after a prewash of the gut lumen and could be restored by the addition of ascorbate to the incubation medium. 6. The conclusion was drawn from these results that luminal reduction precedes ferric iron absorption and that this is a prerequisite for the uptake into the mucosa.

Albumins↗

PubMed1987

Cellular and paracellular calcium transport in the rat ileum and the influence of 1 alpha, 25-dihydroxyvitamin D3 and dexamethasone.

Concentration dependence of unidirectional calcium fluxes across the rat ileum freed from the serosa and the muscularis externa were measured in a modified Ussing-chamber. Mucosa (m) to serosa (s) calcium flux showed a saturable component, whereas s to m calcium flux was linearly related to the calcium concentration between 0.125 mmol/l and 5 mmol/l. At all calcium concentrations used net secretion of calcium was observed. The s to m flux of the simultaneously measured paracellular marker mannitol at all calcium concentrations was remarkably higher than the m to s flux, resulting in net mannitol secretion. The results obtained from the calcium fluxes when clamping the transepithelial electrical potential agree well with those of the concentration dependence of the calcium fluxes: 1. Only m to s flux has a voltage independent, transcellular component. 2. Calcium s to m flux is totally voltage dependent, i.e. diffusive. 3. Diffusional s to m calcium flux is about 80% greater than the diffusional fraction of the m to s flux. Omitting glucose from the bathing solution effected a decrease of the transepithelial electrical potential and of the short circuit by 91% and 85% respectively; net calcium secretion was almost abolished and net mannitol secretion remarkably reduced. Addition of glucose, which stimulates water absorption in the ileum as a metabolic substrate, activated m to s but significantly more pronounced s to m calcium flux parallel to that of mannitol.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Properties of an anion-selective channel from rat colonic enterocyte plasma membranes reconstituted into planar phospholipid bilayers.

Vesicles derived from epithelial cells of the colonic mucosa of the rat were fused to planar phospholipid bilayer membranes, revealing spontaneously switching anion-conducting channels of 50 pS conductance (at -30 mV with 200 mM Cl- each side). The equilibrium selectivity series was I- (1.7)/Br- (1.3)/Cl- (1.0)/F- (0.4)/HCO3- (0.4)/Na (less than 0.11). Only one dominant open-state conductance could be resolved, which responded linearly to Cl- concentrations up to 600 mM. The single-channel current-voltage curve was weakly rectifying with symmetrical solutions. When 50 mV were exceeded at the high-conductance branch of the curve, switching was arrested in the closed state. At more moderate voltages (+/- 40 mV) kinetics were dominated by one open state of about 35-msec lifetime and two closed states of about 2 and 9-msec lifetime. Of these, the more stable closed state occurred less often. At these voltages one additional closed state of significantly longer lifetime (greater than 0.5 sec) was observed.

Animals↗

PubMed1987

The cadmium effect on iron absorption.

Test solutions of cadmium and labeled iron salts, soluble complexes of diferric transferrin, or hemoglobin iron were introduced orally or were injected into tied-off jejunal segments in rat. Cadmium reduced the absorption of iron salts to about half in both normal and iron-deficient rats. Hemoglobin iron absorption was enhanced, indicating that the processing of this form or iron and its release from mucosa to blood was intact. A greater reduction in iron absorption occurred in iron-deficient rats when transferrin iron was injected into gut loops. Mucosal radioiron content in animals given cadmium with either iron salts or transferrin iron was increased. The primary effect of cadmium was on intracellular processing of iron salts and transferrin iron. The major portion of cadmium taken up by the mucosa of normal animals was bound to ferritin, and the effect of cadmium within the mucosal cell may be reduced thus.

Animals↗

PubMed1987

Calcium transport across the colon ascendens and the influence of 1,25-dihydroxyvitamin D3 and dexamethasone.

Concentration dependence of unidirectional calcium fluxes across the rat colon ascendens were measured in a modified Ussing chamber. Both the mucosa (m) to serosa (s) and the s to m calcium flux exhibited saturation kinetics. The maximum transport rates and the affinity to the transporter of calcium was higher in the m to s direction than that from s to m, resulting in a remarkable net calcium absorption. The results obtained from measurements of unidirectional calcium fluxes in dependence on clamped transepithelial potentials showed that: (i) calcium transport in both direction had a voltage-independent component; (ii) the voltage-independent, i.e. non diffusive fraction of the m to s calcium flux was 3.2 times greater than that in the opposite direction; (iii) the voltage dependent, i.e. diffusional fraction of the m to s calcium flux, was about two times greater than the voltage-dependent fraction of the calcium flux in the s to m direction; and (iv) in the m to s direction 62%, and the s to m direction 73%, of the total unidirectional flux was voltage-dependent. Dexamethasone, known to enhance sodium and water absorption in the colon, had no significant influence on net calcium absorption but increased the unidirectional calcium fluxes in both directions. The increase in unidirectional calcium fluxes parallel to that of the extracellular marker mannitol suggests that dexamethasone has no influence on the transcellular calcium transport but increases the calcium flux along the paracellular way. Amiloride had no influence on the dexamethasone-induced changes of the epithelial electrical parameters as distinguished from the colon descendens.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗

PubMed1987

In vitro effects of dexamethasone on sodium transport across rat colon.

1. The in vitro effects of dexamethasone on Na+ transport across the colon descendens from normal rats was investigated. Amiloride was used at two concentrations, 10 microM and 1 mM, to differentially inhibit the transport of Na+ across the colon. The colon descendens from each rat was divided into four segments and Na+ unidirectional fluxes before and 7 h after the addition of dexamethasone (10(-6) M) were determined under short-circuit conditions. 2. Base-line JnetNa (net flux of Na+) was twice as high in the proximal segment as in the distal segment. The two middle segments had intermediate rates of Na+ transport. JnetNa in control tissue was unaffected by 10 microM-amiloride but was completely inhibited by 1 mM-amiloride. In control tissue, amiloride at either 10 microM or 1 mM had no effect on the transmural potential difference (p.d.), the transmural conductance (Gt) or the short-circuit current (Isc). 3. Dexamethasone caused a time-dependent increase in the p.d. and in the Isc in all four segments of the colon. The increase in the p.d. and Isc was greatest in the most distal segment and less in each of the successive more proximal segments. This segmental difference along the colon was observed in tissue from all animals studied (n greater than 30). 4. The increase in p.d. and Isc caused by dexamethasone was accompanied by an increase in JnetNa to the same maximum rate of 14 mu equiv cm-2 h-1 in each segment.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗

PubMed1986

Inhibition of the intestinal transport of uracil by hexoses and amino acids.

Various hexoses and amino acids were tested as potential inhibitors of the active mucosal to serosal transport of uracil across the everted rat jejunum. Uracil transport displayed Michaelis-Menten type kinetics with a Vmax of 10.4 +/- 0.2 mumol X g-1 X h-1 and an apparent Km of 0.047 +/- 0.002 mM (means +/- S.D.). Scilliroside, an inhibitor of the basolateral (Na+ + K+)-ATPase, dose-dependently inhibited the transport of uracil consistent with the Na+ dependency of uracil transport. Thymine was a full competitive inhibitor (Ki = 0.021 +/- 0.002 mM) of uracil transport. All actively transported substances tested including L-phenylalanine, L-leucine, D-galactose, D-glucose, and 3-O-methylglucose inhibited the transport of uracil. In contrast, L-glucose and fructose, substances which are not actively transported, were without effect on uracil transport. Further studies with D-galactose indicated that it acts as a partial noncompetitive inhibitor (Ki = 6.0 +/- 1.4 mM) of uracil transport. This Ki is in good agreement with the apparent Kt (5.8 +/- 1.1 mM) for D-galactose transport. Phlorizin (0.1 mM), an inhibitor of galactose transport, blocked the inhibitory effect of galactose on uracil transport. In the ileum D-galactose had no effect on uracil transport but thymine caused the same degree of inhibition as in the jejunum. The results demonstrate that heterologous inhibition is a more general phenomenon than had previously been realized.

Amino Acids↗