Keratins modulate colonocyte electrolyte transport via protein mistargeting

The function of intestinal keratins is unknown, although keratin 8 (K8)–null mice develop colitis, hyperplasia, diarrhea, and mistarget jejunal apical markers. We quantified the diarrhea in K8-null stool and examined its physiologic basis. Isolated crypt-units from K8-null and wild-type mice have similar viability. K8-null distal colon has normal tight junction permeability and paracellular transport but shows decreased short circuit current and net Na absorption associated with net Cl secretion, blunted intracellular Cl/HCO3-dependent pH regulation, hyperproliferation and enlarged goblet cells, partial loss of the membrane-proximal markers H,K-ATPase-β and F-actin, increased and redistributed basolateral anion exchanger AE1/2 protein, and redistributed Na-transporter ENaC-γ. Diarrhea and protein mistargeting are observed 1–2 d after birth while hyperproliferation/inflammation occurs later. The AE1/2 changes and altered intracellular pH regulation likely account, at least in part, for the ion transport defects and hyperproliferation. Therefore, colonic keratins have a novel function in regulating electrolyte transport, likely by targeting ion transporters to their cellular compartments.

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Corticosteroid alteration of active electrolyte transport in rat distal colon

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1983.245.5.g668 ◽

1983 ◽

Vol 245 (5) ◽

pp. G668-G675 ◽

Cited By ~ 8

Author(s):

E. S. Foster ◽

T. W. Zimmerman ◽

J. P. Hayslett ◽

H. J. Binder

Keyword(s):

Colonic Mucosa ◽

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Transport Processes ◽

Electrolyte Transport ◽

Sodium Absorption ◽

Rat Distal Colon ◽

Potassium Absorption ◽

Potassium Secretion

To determine the effect of corticosteroids on active transport processes, unidirectional fluxes of 22Na, 36Cl, and 42K were measured under short-circuit conditions across isolated stripped distal colonic mucosa of the rat in control, secondary hyperaldosterone, and dexamethasone-treated animals. In controls net sodium and chloride fluxes (JNanet and JClnet) and short-circuit current (Isc) were 6.6 +/- 2.2, 7.6 +/- 1.6, and 1.3 +/- 0.2 mu eq X h-1 X cm-2, respectively. Although aldosterone increased Isc to 7.3 +/- 0.5 mu eq X h-1 X cm-2, JNanet (6.9 +/- 0.7 mu eq X h-1 X cm-2) was not altered and JClnet was reduced to 0 compared with controls. Dexamethasone also stimulated Isc but did not inhibit JClnet. In Cl-free Ringer both aldosterone and dexamethasone produced significant and equal increases in JNanet and Isc. Theophylline abolished JNanet in control animals but not in the aldosterone group. Aldosterone reversed net potassium absorption (0.58 +/- 0.11 mu eq X h-1 X cm-2) to net potassium secretion (-0.94 +/- 0.08 mu eq X h-1 X cm-2). Dexamethasone reduced net potassium movement to 0 (-0.04 +/- 0.12 mu eq X h-1 X cm-2). These studies demonstrate that 1) corticosteroids stimulate electrogenic sodium absorption and 2) aldosterone, but not dexamethasone, inhibits neutral NaCl absorption and stimulates active potassium secretion. The effects of mineralocorticoids and glucocorticoids on electrolyte transport are not identical and may be mediated by separate and distinct mechanisms.

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Regulation of electrolyte transport with IL-1β in rabbit distal colon

Mediators of Inflammation ◽

10.1155/s0962935195000111 ◽

1995 ◽

Vol 4 (1) ◽

pp. 61-66 ◽

Cited By ~ 6

Author(s):

F. R. Homaidan ◽

H. Desai ◽

L. Zhao ◽

G. Broutman ◽

R. Burakoff

Keyword(s):

Inflammatory Bowel Disease ◽

Protein Synthesis ◽

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Chloride Secretion ◽

Electrolyte Transport ◽

Interleukin 1Β ◽

Prostaglandin E ◽

Inflammatory Bowel

Interletrkin-1β levels are elevated in inflammatory bowel disease. In this study the mechanism by which interleukin-1β affects electrolyte transport in the rabbit distal colon, was investigated. Interleukin-1β caused a delayed increase in short-circuit current (Isc) which was attributed to protein synthesis since the effect was inhibited by cycloheximide. The interleukin-1β induced increase in Iscwas not affected by amiloride treatment but was completely inhibited by bumetanide or in chloride-free buffer and by indomethacin. Prostaglandin E2levels increased in tissue treated with interleukin-1β, but this increase was reversed by cycloheximide. These data suggest that interleukin-1β causes its effect via a yet to be identified second messenger, by increasing chloride secretion through a prostaglandin E2mediated mechanism.

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Regulation of colonic ion transport by GRP. II. GRP modulates the epithelial response to PGE2

AJP Cell Physiology ◽

10.1152/ajpcell.1996.270.3.c859 ◽

1996 ◽

Vol 270 (3) ◽

pp. C859-C865 ◽

Cited By ~ 6

Author(s):

T. R. Traynor ◽

S. M. O'Grady

Keyword(s):

Time Course ◽

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Electrolyte Transport ◽

Gastrin Releasing Peptide ◽

Transcellular Pathway ◽

Flux Measurements ◽

Pg E2 ◽

Distal Colon Epithelium

The purpose of this study was to examine the potential modulatory effects of gastrin-releasing peptide (GRP) on prostaglandin (PG) E2-stimulated electrolyte transport across the distal colon epithelium. In an earlier study, PGE2 was shown to reduce net Cl absorption without altering the serosal-to-mucosal unidirectional Cl flux in porcine distal colon (19). In the present study, tissues were pretreated with serosal or mucosal GRP and subsequently stimulated with PGE2. The resulting increase in short-circuit current (ISC) was 152% (serosal GRP) and 49% (mucosal GRP) greater than control PGE2 responses alone. Serosal, but not mucosal, GRP also enhanced the ISC response to vasoactive intestinal peptide. On the basis of flux measurements, the combined effects of serosal GRP and PGE2 resulted in the activation of a transcellular pathway for Cl secretion, which was not activated by either mediator alone. The time course of the PGE2 response was also affected by GRP. Serosal GRP shortened the time to maximum ISC by 35%, whereas mucosal peptide lengthened the time to maximum ISC by 68% These results suggest that GRP acts as a modulator of PG action on electrolyte transport in the distal colon.

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Genistein activates CFTR-mediated Cl−secretion in the murine trachea and colon

AJP Cell Physiology ◽

10.1152/ajpcell.2000.279.2.c383 ◽

2000 ◽

Vol 279 (2) ◽

pp. C383-C392 ◽

Cited By ~ 24

Author(s):

Catharine A. Goddard ◽

Martin J. Evans ◽

William H. Colledge

Keyword(s):

Cystic Fibrosis ◽

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Transmembrane Conductance Regulator ◽

Wild Type ◽

Transmembrane Conductance ◽

Cell Systems ◽

Cl Secretion ◽

Cystic Fibrosis Transmembrane

The action of the isoflavone genistein on the cystic fibrosis transmembrane conductance regulator (CFTR) has been studied in many cell systems but not in intact murine tissues. We have investigated the action of genistein on murine tissues from normal and cystic fibrosis (CF) mice. Genistein increased the short-circuit current ( I sc) in tracheal (16.4 ± 2.8 μA/cm2) and colonic (40.0 ± 4.4 μA/cm2) epithelia of wild-type mice. This increase was inhibited by furosemide, diphenylamine-2-carboxylate, and glibenclamide, but not by DIDS. In contrast, genistein produced no significant change in the I sc of the tracheal epithelium (0.9 ± 1.1 μA/cm2) and decreased the I sc of colons from CF null (−13.1 ± 2.3 μA/cm2) and ΔF508 mice (−10.3 ± 1.3 μA/cm2). Delivery of a human CFTRcDNA-liposome complex to the airways of CF null mice restored the genistein response in the tracheas to wild-type levels. Tracheas from ΔF508 mice were also studied: 46% of trachea showed no response to genistein, whereas 54% gave an increase in I scsimilar to that in wild type. We conclude that genistein activates CFTR-mediated Cl− secretion in the murine trachea and distal colon.

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Colonic H+-K+-ATPase in K+conservation and electrogenic Na+ absorption during Na+ restriction

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.2001.281.6.g1369 ◽

2001 ◽

Vol 281 (6) ◽

pp. G1369-G1377 ◽

Cited By ~ 21

Author(s):

Zachary Spicer ◽

Lane L. Clarke ◽

Lara R. Gawenis ◽

Gary E. Shull

Keyword(s):

Knockout Mice ◽

Apical Membrane ◽

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Wild Type ◽

Restricted Diet ◽

Serum Aldosterone

Upregulation of the colonic H+-K+- ATPase (cHKA) during hyperaldosteronism suggests that it functions in both K+conservation and electrogenic Na+ absorption in the colon when Na+-conserving mechanisms are activated. To test this hypothesis, wild-type ( cHKA +/+) and cHKA-deficient ( cHKA −/−) mice were fed Na+-replete and Na+-restricted diets and their responses were analyzed. In both genotypes, Na+ restriction led to reduced plasma Na+ and increased serum aldosterone, and mRNAs for the epithelial Na+ channel (ENaC) β- and γ-subunits, channel-inducing factor, and cHKA were increased in distal colon. Relative to wild-type controls, cHKA −/− mice on a Na+-replete diet had elevated fecal K+ excretion. Dietary Na+restriction led to increased K+ excretion in knockout but not in wild-type mice. The amiloride-sensitive, ENaC-mediated short-circuit current in distal colon was significantly reduced in knockout mice maintained on either the Na+-replete or Na+-restricted diet. These results demonstrate that cHKA plays an important role in K+ conservation during dietary Na+ restriction and suggest that cHKA-mediated K+ recycling across the apical membrane is required for maximum electrogenic Na+ absorption.

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Active electrolyte transport in mammalian buccal mucosa

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1988.255.3.g286 ◽

1988 ◽

Vol 255 (3) ◽

pp. G286-G291 ◽

Cited By ~ 3

Author(s):

R. C. Orlando ◽

N. A. Tobey ◽

V. J. Schreiner ◽

R. D. Readling

Keyword(s):

Buccal Mucosa ◽

Short Circuit ◽

Basolateral Membrane ◽

Electrical Potential ◽

Short Circuit Current ◽

Electrolyte Transport ◽

Electrical Potential Difference ◽

Ussing Chambers ◽

Net Fluxes

The transmural electrical potential difference (PD) was measured in vivo across the buccal mucosa of humans and experimental animals. Mean PD was -31 +/- 2 mV in humans, -34 +/- 2 mV in dogs, -39 +/- 2 mV in rabbits, and -18 +/- 1 mV in hamsters. The mechanisms responsible for this PD were explored in Ussing chambers using dog buccal mucosa. After equilibration, mean PD was -16 +/- 2 mV, short-circuit current (Isc) was 15 +/- 1 microA/cm2, and resistance was 1,090 +/- 100 omega.cm2, the latter indicating an electrically "tight" tissue. Fluxes of [14C]mannitol, a marker of paracellular permeability, varied directly with tissue conductance. The net fluxes of 22Na and 36Cl were +0.21 +/- 0.05 and -0.04 +/- 0.02 mueq/h.cm2, respectively, but only the Na+ flux differed significantly from zero. Isc was reduced by luminal amiloride, serosal ouabain, or by reducing luminal Na+ below 20 mM. This indicated that the Isc was determined primarily by active Na+ absorption and that Na+ traverses the apical membrane at least partly through amiloride-sensitive channels and exits across the basolateral membrane through Na+-K+-ATPase activity. We conclude that buccal mucosa is capable of active electrolyte transport and that this capacity contributes to generation of the buccal PD in vivo.

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Pharmacological modulation of ion transport across wild-type and ΔF508 CFTR-expressing human bronchial epithelia

AJP Cell Physiology ◽

10.1152/ajpcell.2000.279.2.c461 ◽

2000 ◽

Vol 279 (2) ◽

pp. C461-C479 ◽

Cited By ~ 130

Author(s):

Daniel C. Devor ◽

Robert J. Bridges ◽

Joseph M. Pilewski

Keyword(s):

Cystic Fibrosis ◽

Ion Transport ◽

Short Circuit ◽

Primary Cultures ◽

Short Circuit Current ◽

Bronchial Epithelium ◽

Disulfonic Acid ◽

Wild Type ◽

Pharmacological Agents ◽

Transport Defect

Forskolin, UTP, 1-ethyl-2-benzimidazolinone (1-EBIO), NS004, 8-methoxypsoralen (Methoxsalen; 8-MOP), and genistein were evaluated for their effects on ion transport across primary cultures of human bronchial epithelium (HBE) expressing wild-type (wt HBE) and ΔF508 (ΔF-HBE) cystic fibrosis transmembrane conductance regulator. In wt HBE, the baseline short-circuit current ( I sc) averaged 27.0 ± 0.6 μA/cm2 ( n = 350). Amiloride reduced this I sc by 13.5 ± 0.5 μA/cm2 ( n = 317). In ΔF-HBE, baseline I sc was 33.8 ± 1.2 μA/cm2 ( n = 200), and amiloride reduced this by 29.6 ± 1.5 μA/cm2 ( n = 116), demonstrating the characteristic hyperabsorption of Na+ associated with cystic fibrosis (CF). In wt HBE, subsequent to amiloride, forskolin induced a sustained, bumetanide-sensitive I sc(Δ I sc = 8.4 ± 0.8 μA/cm2; n = 119). Addition of acetazolamide, 5-( N-ethyl- N-isopropyl)-amiloride, and serosal 4,4′-dinitrostilben-2,2′-disulfonic acid further reduced I sc, suggesting forskolin also stimulates HCO3 − secretion. This was confirmed by ion substitution studies. The forskolin-induced I scwas inhibited by 293B, Ba2+, clofilium, and quinine, whereas charybdotoxin was without effect. In ΔF-HBE the forskolin I sc response was reduced to 1.2 ± 0.3 μA/cm2 ( n = 30). In wt HBE, mucosal UTP induced a transient increase in I sc (Δ I sc = 15.5 ± 1.1 μA/cm2; n = 44) followed by a sustained plateau, whereas in ΔF-HBE the increase in I sc was reduced to 5.8 ± 0.7 μA/cm2 ( n = 13). In wt HBE, 1-EBIO, NS004, 8-MOP, and genistein increased I sc by 11.6 ± 0.9 ( n = 20), 10.8 ± 1.7 ( n = 18), 10.0 ± 1.6 ( n = 5), and 7.9 ± 0.8 μA/cm2( n = 17), respectively. In ΔF-HBE, 1-EBIO, NS004, and 8-MOP failed to stimulate Cl− secretion. However, addition of NS004 subsequent to forskolin induced a sustained Cl−secretory response (2.1 ± 0.3 μA/cm2, n = 21). In ΔF-HBE, genistein alone stimulated Cl− secretion (2.5 ± 0.5 μA/cm2, n = 11). After incubation of ΔF-HBE at 26°C for 24 h, the responses to 1-EBIO, NS004, and genistein were all potentiated. 1-EBIO and genistein increased Na+ absorption across ΔF-HBE, whereas NS004 and 8-MOP had no effect. Finally, Ca2+-, but not cAMP-mediated agonists, stimulated K+ secretion across both wt HBE and ΔF-HBE in a glibenclamide-dependent fashion. Our results demonstrate that pharmacological agents directed at both basolateral K+ and apical Cl− conductances directly modulate Cl−secretion across HBE, indicating they may be useful in ameliorating the ion transport defect associated with CF.

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Effects of galanin on short circuit current and electrolyte transport in rabbit ileum

Peptides ◽

10.1016/0196-9781(94)90120-1 ◽

1994 ◽

Vol 15 (8) ◽

pp. 1431-1436 ◽

Cited By ~ 11

Author(s):

Fadia R. Homaidan ◽

Shao Hua Tang ◽

Mark Donowitz ◽

Geoffrey W.G. Sharp

Keyword(s):

Short Circuit ◽

Short Circuit Current ◽

Electrolyte Transport ◽

Rabbit Ileum

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Histamine augments colonic secretion in guinea pig distal colon

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1990.258.3.g432 ◽

1990 ◽

Vol 258 (3) ◽

pp. G432-G439 ◽

Cited By ~ 7

Author(s):

Y. Z. Wang ◽

H. J. Cooke ◽

H. C. Su ◽

R. Fertel

Keyword(s):

Short Circuit ◽

Nordihydroguaiaretic Acid ◽

Short Circuit Current ◽

Intestinal Secretion ◽

Distal Colon ◽

H2 Antagonist ◽

Colonic Secretion ◽

Set Up ◽

Colonic Transport

We tested the hypothesis that the role of histamine in the control of intestinal secretion is mediated by prostaglandins (PGs). The effects of histamine on ion transport were examined in muscle-stripped sheets of mucosa/submucosa set up in flux chambers. Histamine evoked a transient concentration-dependent increase in short-circuit current (Isc) that was reduced by the Cl- transport inhibitor bumetanide. Histamine also caused the release of PGE2. The Isc response to histamine was reduced by indomethacin and piroxicam, which block PG formation, but not by nordihydroguaiaretic acid, which prevents production of lipoxygenase products. 2-Methylhistamine, but not dimaprit, evoked a concentration-dependent increase in Isc. The Isc response to histamine was reduced by the H1-blocker pyrilamine, but not by the H2-antagonist cimetidine. In addition to its direct effect, histamine augmented the responses of endogenously released neurotransmitters with and without indomethacin and hexamethonium. Tetrodotoxin (TTX) reduced the Isc response to 10(-3) M histamine. In the presence of TTX, exogenous histamine amplified the responses to PGs, vasoactive intestinal polypeptide, 2-chloroadenosine, bethanechol, and carbachol. These results suggest that histamine acts at H1-receptors on cells within the gut to mediate intestinal Cl- secretion in part by releasing PGs and by augmenting the actions of endogenously released neurotransmitters. Our results indicate that histamine has a role in the regulation of colonic transport function.

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Activation of KCNQ (KV7) K+ channels in enteric neurons inhibits epithelial Cl- secretion in mouse distal colon

AJP Cell Physiology ◽

10.1152/ajpcell.00536.2020 ◽

2021 ◽

Author(s):

Andrew J. Nickerson ◽

Trey S. Rottgen ◽

Vazhaikkurichi M. Rajendran

Keyword(s):

Short Circuit ◽

Short Circuit Current ◽

Distal Colon ◽

Therapeutic Benefit ◽

Enteric Neurons ◽

Intestinal Epithelial ◽

Cell Monolayers ◽

Neuronal Populations ◽

Irritable Bowel

KV7 (KCNQ) K+ channels are expressed in many neuronal populations, and play an important role in regulating membrane potential by generating a hyper-polarizing K+ current and decreasing cell excitability. However, the role of KV7 channels in the neural regulation of intestinal epithelial Cl- secretion is not known. Cl- secretion in mouse distal colon was measured as a function of short circuit current (ISC), while pharmacological approaches were used to test the hypothesis that activation of KV7 channels in enteric neurons would inhibit epithelial Cl- secretion. Flupirtine, a non-selective KV7 activator, inhibited basal Cl- secretion in mouse distal colon and abolished or attenuated the effects of drugs that target various components of enteric neurotransmission, including tetrodotoxin (NaV channel blocker), Veratridine (NaV channel activator), Nicotine (nicotinic acetylcholine receptor agonist) and Hexamethonium (nicotinic antagonist). In contrast, flupritine did not block the response to epithelium-targeted agents VIP (endogenous VPAC receptor ligand) or carbachol (non-selective cholinergic agonist). Flupirtine inhibited Cl- secretion in both full-thickness and seromuscular-stripped distal colon (containing the submucosal, but not myenteric plexus), but generated no response in epithelial T84 cell monolayers. KV7.2 and KV7.3 channel proteins were detected by immunofluorescence in whole-mount preparations of the submucosa from mouse distal colon. ICA 110381 (KV7.2/7.3 specific activator) inhibited Cl- secretion comparably to flupirtine. We conclude that KV7 channel activators inhibit neurally-driven Cl- secretion in the colonic epithelium, and may therefore have therapeutic benefit in treating pathologies associated with hyper-excitable enteric nervous system, such as irritable bowel syndrome with diarrhea (IBS-D).

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