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E B Chang

Publications and source records attributed to E B Chang.

90 records · Page 5Linked to original sources
PubMed1988

Effects of serotonin on Na+-H+ exchange and intracellular calcium in isolated chicken enterocytes.

The effects of serotonin or 5-hydroxytryptamine (5-HT) on Na absorption and intracellular free Ca (Cai) in isolated chicken enterocytes was examined. The rate of initial 22Na uptake was inhibited by 50% after 90 s of stimulation with 5-HT (10(-5) M), an effect that was not additive with amiloride (10(-3) M) and was transient (less than 10 min). 5-HT similarly decreased intracellular pH (pHi) in cells loaded with the pH indicator carboxyfluorescein, an effect that was also transient, not additive with amiloride, and Na dependent. The ED50 of this effect was approximately 10(-8) M. 5-HT also stimulated a transient increase in Cai as determined by quin2 fluorescence. A maximal increase of 60 nM occurred significantly before the peak change in pHi, but the total duration of response was similar in each case. In the absence of extracellular Ca, the 5-HT effects on pHi and Cai still persisted. In cells loaded with the Ca-buffering agent MAPTAM, the 5-HT (10(-5) M) inhibitory effect of 22Na influx was partially inhibited. We conclude that 5-HT directly inhibits Na absorption by isolated enterocytes by releasing endogenous Ca, which subsequently causes an inhibition of amiloride-sensitive Na+-H+ exchange.

Amiloride↗
PubMed1988

Glucose enhancement of transcellular calcium transport in the intestine.

Glucose stimulates calcium transport in vitro in rat duodenal tissue and isolated enterocytes. Under short-circuited conditions, glucose increased mucosal to serosal calcium flux (JCa(m----s)) without altering serosal to mucosal calcium flux (JCa(s----m)) in the duodenum, the primary site of active calcium absorption in the rat small intestine. The half-maximal dose (ED50) of the glucose stimulatory effect was less than 1 mM, and an increase in JCa(m----s) of 80% over control was seen at a glucose concentration of 50 mM. Glucose did not increase calcium flux in the ileum where active calcium absorption is minimal. Glucose stimulated net calcium uptake by 35% in isolated duodenal enterocytes. Glucose did not alter calcium efflux from preloaded enterocytes suspended in calcium-free buffer. Glucose enhancement of net calcium uptake in enterocytes was not caused by altered cell membrane integrity or functional viability. The nonmetabolizable glucose analogue alpha-methylglucoside did not stimulate calcium transport. Our findings suggest that glucose can stimulate intestinal calcium absorption, at least partially, by enhancing transcellular calcium transport and that cellular glucose metabolism is necessary for stimulation of this route of calcium transport.

Animals↗
PubMed1987

Calcium-mediated cyclic AMP inhibition of Na-H exchange in small intestine.

8-Bromo cyclic AMP (cAMP) (10(-4) M) inhibits Na absorption in isolated chicken enterocytes as has been reported previously. Direct measurements of intracellular pH (pHi) using 5,6-carboxyfluorescein diacetate showed that both 8-bromo cAMP and the diuretic amiloride (10(-3) M) stimulated a persistent decrease in pHi of approximately 0.1 pH units, effects that were Na dependent and were not additive when cells were stimulated with both agents. These results suggest inhibition of an amiloride-sensitive Na/H exchange by cAMP. Direct measurements of intracellular Ca [Ca]i were also made using quin 2. 8-Bromo cAMP (10(-4) M) stimulated an immediate and persistent (greater than 10 min) increase in [Ca]i of approximately 20 nM, an effect that was not dependent on extracellular Ca. Pretreatment of cells with the specific calmodulin inhibitor calmidazolium (10(-7) M) and the intracellular Ca-buffering agent MAPTAM blocked cAMP's effects on pH and Na uptake, but did not interfere with amiloride's effects. An increase in [Ca]i stimulated by the Ca ionophore A23187 (10(-6) M) was sufficient by itself to decrease pHi and inhibit amiloride-sensitive Na influx in isolated enterocytes. We conclude that cAMP stimulates the release of endogenous Ca in isolated enterocytes. This increase in [Ca]i appears to be essential for inhibition of amiloride-sensitive Na-H exchange by this cyclic nucleotide.

Alprostadil↗
PubMed1987

Intestinal adaptation to diabetes. Altered Na-dependent nutrient absorption in streptozocin-treated chronically diabetic rats.

To examine the pattern and mechanisms of enhanced intestinal nutrient absorption in diabetes, we measured intestinal transport of 3-O-methylglucose (3OMG), l-alanine (ALA), and SO4 in male Lewis rats made diabetic with streptozocin. Diabetes enhanced 3OMG absorption fivefold in ileum and threefold in jejunum; ALA absorption increased twofold in ileum but not at all in jejunum; ileal SO4 transport was unaffected. Increases in 3OMG and ALA transport were due solely to increases in maximum velocity. The enhancement of ileal glucose absorption was half-maximal in 40-45 d, could be reversed by 10 d of treatment with insulin and did not result from adrenergic denervation. The density of glucose carriers per milligram brush border protein (measured as [3H]phlorizin binding sites) was not altered but there was a sixfold increase in the number of glucose-inhibitable [3H]phlorizin-binding sites in the intact epithelium. Generalized mucosal hypertrophy accounted for less than 30% of this increase. We conclude that the intestine adapts to streptozocin-induced diabetes through recruitment of additional brush border carriers for sugar, probably in the midvillus-to-crypt region.

3-O-Methylglucose↗
PubMed1986

Secretagogue-induced changes in membrane calcium permeability in chicken and chinchilla ileal mucosa. Selective inhibition by loperamide.

Substance P (SP), neurotensin (NT), bombesin (BB), serotonin (5HT), and carbamylcholine (CCH) transiently increase electrogenic anion secretion in chinchilla and chicken ileum. SP and CCH also transiently inhibit amiloride-sensitive Na/H exchange in isolated chicken enterocytes. Loperamide (LP) inhibits the short-circuit current responses caused by SP, NT, and BB, but not those caused by CCH, 5HT, Ca ionophore, or cyclic nucleotides. Similarly, LP inhibits the effects of SP, but not those of CCH, on Na/H exchange. LP inhibition of the SP effects was further studied in isolated chicken enterocytes. CCH and SP transiently increased cytosolic Ca activity by 20-50 nmol/liter, but only the response to SP was inhibited by LP (10(-5) M) and by the absence of extracellular Ca. We conclude SP and CCH effects on intestinal electrolyte transport are mediated by increasing enterocyte Ca activity and LP specifically inhibits peptide hormone-activated Ca entry by an opiate receptor-independent mechanism.

Amiloride↗
PubMed1986

Experimental diabetic diarrhea in rats. Intestinal mucosal denervation hypersensitivity and treatment with clonidine.

Diarrhea in streptozocin-induced chronically diabetic rats is caused by an impaired adrenergic regulation of intestinal fluid and electrolyte transport. Stimulation of alpha 2-adrenergic receptors on enterocytes normally promotes NaCl absorption and inhibits HCO3 secretion. The purpose of this study was to determine if adrenergic denervation of intestinal mucosa in chronically diabetic rats alters postsynaptic receptor response, and if the alpha 2-adrenergic agonist clonidine could correct observed fluid malabsorption. Mucosal norepinephrine stores, a measure of adrenergic tone, were markedly reduced in diabetic rats compared with nondiabetic littermates. In vitro, short-circuit current changes to exogenously added l-epinephrine were significantly greater in diabetics, suggesting that denervation hypersensitivity was due to increased numbers of postsynaptic alpha 2-adrenergic receptors. In vivo loop studies demonstrated net fluid secretion in the ileum and colon of diabetics. In diabetics, clonidine reversed the secretion to absorption, but it had no effect on fluid absorption in controls. We conclude that diabetic diarrhea in streptozocin-induced chronically diabetic rats is due to impaired adrenergic regulation of mucosal ion transport, accompanied by a postsynaptic denervation hypersensitivity that can be reversed by clonidine, and accompanied by net intestinal fluid secretion that can be effectively reversed with clonidine.

Adrenergic alpha-Agonists↗
PubMed1985

The pharmacological modification of secretory responses.

Electrolyte transport across the intestinal mucosa can be modulated by several neurotransmitters, hormones and drugs. Opiate agonists and endogenous opioid peptides inhibit electrolyte secretion both in vitro and in vivo. These drugs appear to act at several levels. Thus, opioid effects can be elicited at the local mucosal level. Secondly, antisecretory effects can be demonstrated when opioids are administered into the brain. These central effects appear to involve activation of the sympathetic innervation of the intestine. Thirdly, some antidiarrhoeal drugs such as loperamide may have ancillary non-opiate-like actions that contribute to their effectiveness. In cases of inflammatory bowel disease where local concentrations of inflammatory mediators such as kinins and eicosanoids may be high, non-steroidal anti-inflammatory drugs may be effective in treating diarrhoeal symptoms. The existence of many types of receptors on mucosal cells indicates that several pharmacological approaches exist for the potential modulation of electrolyte transport.

Animals↗
PubMed1985

Phorbol ester stimulation of active anion secretion in intestine.

Phorbol 12,13-dibutyrate (PDB) stimulates electrogenic anion secretion in rabbit and chicken distal ileum. The 50% effective dose in each case was 15 nM, and the maximal short-circuit current (Isc) responses seen at 10(-6) M were 20 and 140 microA/cm2, respectively. Isc was also stimulated by the diacylglycerol 1-oleoyl-2-acetyl glycerol (10(-5) M) but not by the inactive phorbol ester analogue 4 alpha-phorbol 12,13-didecanoate. Removal of Ca from the serosal bathing medium and pretreatment of tissues with atropine (10(-6) M) or tetrodotoxin (2 X 10(-7) M) did not affect PDB-stimulated responses. PDB also did not alter basal intracellular free Ca levels in isolated chicken enterocytes loaded with quin 2 or basal adenosine 3',5'-cyclic monophosphate levels in intact tissues from rabbit and chicken. In the presence of PDB, Ca- and phospholipid-dependent phosphorylation of several proteins in particulate and soluble fractions from isolated chicken enterocytes were seen. Pretreatment of chicken and rabbit tissues with indomethacin or mepacrine inhibited the Isc responses to PDB and carbamylcholine, suggesting a role for prostaglandins. These results suggest that electrogenic anion secretion stimulated by phorbol esters and diacylglycerol may be mediated by activation of protein kinase C.

Animals↗
PubMed1985

Phorbol ester inhibition of Na-H exchange in rabbit proximal colon.

In rabbit proximal colon, in vitro addition of phorbol 12,13-dibutyrate (PDB, 10(-7) M) to the serosal bathing medium inhibits mucosal (m)-to-serosal (s) unidirectional Na flux (JsmNa) without altering JsmNa or unidirectional Cl fluxes. Similar results were obtained when amiloride (2 X 10(-4) M) was added to the mucosal bathing medium. No additivity of effect was seen when tissues were exposed to both agents. Measurements with carboxyfluorescein reveal that the two agents cause equal decreases of intracellular pH (pHi), an effect that is dependent on the presence of extracellular Na (Na replacement also decreases pHi). No additivity of pHi effects is seen when both agents are added together. To determine the membrane site of this PDB-inhibitable Na-H exchange, Na influx across the luminal border of proximal colon was measured and was found to be inhibited equally by PDB and amiloride. We conclude that PDB, by activation of protein kinase C, inhibits electro-neutral amiloride-sensitive Na-H exchange in the luminal membrane of proximal colon.

Animals↗
PubMed1985

Diarrhea in streptozocin-treated rats. Loss of adrenergic regulation of intestinal fluid and electrolyte transport.

Diarrhea was noted in rats with streptozocin-induced chronic diabetes. We have investigated the possibility that this diarrhea is a consequence of altered neuronal control of water and electrolyte absorption in the intestinal epithelium. In particular, we examined noradrenergic control because alpha-2-adrenergic agonists are known to stimulate intestinal fluid absorption. When compared with nondiabetic littermates, chronically diabetic rats exhibited significant impairment of fluid absorption by the ileum and colon, but not the jejunum. This impairment of intestinal fluid absorption was not found in either insulin-treated or untreated acutely diabetic (7 d) animals. Mucosal histology appeared normal in all of the above groups. Mucosal norepinephrine stores in the jejunum and ileum of chronically diabetic rats were estimated in vitro by the short-circuit current (Isc) response to tyramine, an agent that effectively releases stored norepinephrine. Pargyline was added to inhibit enzymatic destruction of the added tyramine. In chronically diabetic rats, the Isc response to tyramine was significantly decreased in ileum, but not in jejunum. However, when these responses were expressed as a fraction of the maximal Isc tissue response to exogenously added epinephrine, significant decreases were noted in both ileum and jejunum. In tissues from acutely diabetic rats, Isc responses to tyramine and epinephrine were no different from controls. When sympathetic denervation was produced in nondiabetic rats by treatment with 6-OH-dopamine, the pattern of impaired fluid absorption that developed was the same as that observed in chronically diabetic rats. We conclude that impaired intestinal mucosal absorption of fluid and electrolytes slowly develops in rats made diabetic with streptozocin and that this absorptive impairment is due to a loss of normally present noradrenergic innervation of enterocytes.

Animals↗
PubMed1985

Treatment of diabetic diarrhea with clonidine.

Stimulation of alpha 2-adrenergic receptors on enterocytes promotes fluid and electrolyte absorption and inhibits anion secretion. Loss of adrenergic innervation may play a role in impaired intestinal fluid and electrolyte absorption in diabetic patients with autonomic neuropathy. Clonidine, an alpha 2-adrenergic agonist, was used to treat three patients with "idiopathic" diabetic diarrhea after other treatments had failed: The volume of diarrhea declined significantly (p less than 0.01). Diarrhea recurred when the drug was withdrawn, but the patient's condition improved again when clonidine treatment was reintroduced. Hypotension did not occur as a side effect presumably because of the autonomic neuropathy of these patients.

Chronic Disease↗
PubMed1984

An antiabsorptive basis for precipitated withdrawal diarrhea in morphine-dependent rats.

Diarrhea is a common manifestation of withdrawal from opiates in dependent subjects. This study examined the possibility that this diarrhea results in part from alterations in intestinal fluid transport. Isolated loops of jejunum, ileum and colon were created in morphine-dependent and nondependent rats implanted s.c. with morphine or lactose pellets, respectively. The administration of naltrexone (1 mg/kg s.c.) or its quaternary analog methylnaltrexone (0.01-3 mg/kg i.v.), which does not readily cross the blood-brain barrier, produced a dose-related reduction in fluid absorption from the jejunum and colon of dependent animals only. Similar effects were observed after the i.c.v. injection of quaternary naltrexone (1.0-10 microgram/rat). Both narcotic antagonists, given by any route, produced no change in ileal absorption. Pretreatment with hexamethonium (10 mg/kg i.v.) or atropine (4 mg/kg i.v.) attenuated the antiabsorptive effects of quaternary naltrexone on the jejunum. Serosal addition of naltrexone (10 microM) had no effect on Na or Cl fluxes, short-circuit current or tissue conductance across isolated segments of intestinal mucosa from dependent and nondependent rats. These results indicate that precipitated opiate withdrawal is associated with decreases in jejunal and colonic fluid absorption mediated at sites within both the central nervous system and periphery. Moreover, these effects are not a consequence of a direct opiate action on enterocytes.

Animals↗
PubMed1983

Enterocyte alpha 2-adrenergic receptors: yohimbine and p-aminoclonidine binding relative to ion transport.

We previously reported that alpha 2-adrenergic agonists enhance absorption and inhibit secretion of electrolytes in small intestine. The present study was undertaken to characterize and localize the relevant receptors. Plasma membranes derived from isolated rabbit ileal epithelial cells were incubated with either [3H]yohimbine (Yo), an alpha 2-antagonist, or p-[3H]aminoclonidine (PAC), an alpha 2-agonist. Scatchard analysis of [3H]Yo binding suggests a single receptor. Competitive displacement of Yo from this receptor by other ligands had a potency order characteristic for alpha 2-receptors in other tissue systems. A Scatchard plot of [3H]PAC binding was curvilinear and best fit by assuming two independent site. Competitive displacement of [3H]PAC by PAC in the presence of 140 mM Na+ or 0.1 mM GTP increased the IC50 for PAC binding from 10 nM to 100 and 105 nM, respectively, and the Hill coefficient from 0.7 to 1.2 and 1.0, respectively. The ED50 for PAC effect on short-circuit current (200 nM) does not differ significantly from these values. We conclude that alpha 2-receptors are present on ileal enterocytes and that these receptors mediate enterocyte fluid and electrolyte transport function.

Animals↗
PubMed1982

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

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.

Animals↗
PubMedDate not supplied

Cell-specific induction of hsp72-mediated protection by glutamine against oxidant injury in IEC18 cells.

Glutamine is a major metabolic fuel and trophic agent for intestinal epithelial cells that can enhance intestinal epithelial cell survival against oxidant and thermal stress, possibly through the induction of heat shock protein 72 (hsp72). In this study, we examined the possibility of a direct causal relationship and tissue specificity of glutamine-induced hsp72. Glutamine treatment of intestinal (epithelial) IEC18 cells, but not HeLa (epidermoid) cells, induces the production of hsp72 in a concentration-dependent fashion, without affecting the expression of the constitutively expressed heat shock protein, hsc73. To determine the specific role that hsp72 induction by glutamine plays in resistance of IEC18 cells to oxidant injury, stable transfected cells expressing an hsp72 antisense construct were established. Although thermal induction of hsp72 was blocked only partially by the antisense construct, glutamine induction of hsp72 was completely inhibited. This was associated with a loss of the protective effects of glutamine against oxidant-induced stress. Thus, glutamine specifically induces hsp72 in intestinal epithelial cells, which mediates cell protection against inflammation-induced stress such as oxidants.

Animals↗