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Jeffrey B Matthews

Publications and source records attributed to Jeffrey B Matthews.

34 records · Page 2Linked to original sources
PubMed2003

Ammonium effects on colonic Cl- secretion: anomalous mole fraction behavior.

A significant amount of ammonium (NH4+) is absorbed by the colon. The nature of NH4+ effects on transport and NH4+ transport itself in colonic epithelium is poorly understood. The goal of this study was to elucidate the effects of NH4+ on cAMP-stimulated Cl- secretion in the colonic cell line T84. In HEPES-buffered solutions, application of basolateral NH4+ resulted in a reduced level of Cl- secretory current. The effect of NH4+ appears to occur by at least three mechanisms: 1) basolateral membrane depolarization, 2) a competitive effect with K+, and 3) a long-term (>20 min) increase in transepithelial resistance (TER). The competitive effect with K+ exhibits anomalous mole fraction behavior. Transepithelial current relative to that in 10 mM basolateral K+ was inhibited 15% by 10 mM NH4+ alone and by 30% with a mixture of 2 mM K+ and 8 mM NH4+. A mole fraction mix of 2 mM K+:8 mM NH4+ produced a greater inhibition of basolateral membrane K+ current than pure K+ or NH4+ alone. Similar anomalous behavior was also observed for inhibition of bumetanide-sensitive 36Cl- uptake, e.g., Na+-K+-2Cl- -cotransporter (NKCC-1). No anomalous effect was observed on Na+-K+-ATPase current. Both NKCC-1 and Na+-K+-ATPase activity were elevated in 10 mM NH4+ with respect to 10 mM K+. The effect on TER did not exhibit anomalous mole fraction behavior. The overall effect of basolateral NH4+ on cAMP-stimulated transport is dependent on the [K+]o /[NH4+]o ratio at the basolateral membrane, where o is outside of the cell.

Cell Line↗
PubMed2003

Bryostatin-1 enhances barrier function in T84 epithelia through PKC-dependent regulation of tight junction proteins.

Protein kinase C (PKC) is known to regulate epithelial barrier function. However, the effect of specific PKC isozymes, and their mechanism of action, are largely unknown. We determined that the nonphorbol ester PKC agonist bryostatin-1 increased transepithelial electrical resistance (TER), a marker of barrier function, in confluent T84 epithelia. Bryostatin-1, which has been shown to selectively activate PKC-alpha, -epsilon, and -delta (34), was associated with a shift in the subcellular distribution of the tight junction proteins claudin-1 and ZO-2 from a detergent-soluble fraction into a detergent-insoluble fraction. Bryostatin-1 also led to the appearance of a higher-molecular-weight form of occludin previously shown to correspond to protein phosphorylation. These changes were attenuated by the conventional and novel PKC inhibitor Gö-6850 but not the conventional PKC inhibitor Gö-6976 or the PKC-delta inhibitor röttlerin, implicating a novel isozyme, likely PKC-epsilon. The results suggest that enhanced epithelial barrier function induced by bryostatin-1 involves a PKC-epsilon-dependent signaling pathway leading to recruitment of claudin-1 and ZO-2, and phosphorylation of occludin, into the tight junctional complex.

Bryostatins↗
PubMed2003

Total pancreatectomy and autologous islet cell transplantation as a means to treat severe chronic pancreatitis.

Autologous islet cell transplantation after near-total or total pancreatic resection can alleviate pain in patients with severe chronic pancreatitis and preserve endocrine function. From February 2000 to February 2003, a total of 22 patients, whose median age was 38 years, underwent pancreatectomy and autologous islet cell transplantation. Postoperative complications, metabolic studies, insulin usage, pain scores, and quality of life were recorded for all of these patients. The average number of islet cells harvested was 245,457 (range 20,850 to 607,466). Operative data revealed a mean estimated blood loss of 635 ml, an average operative time of 9 hours, and a mean length of hospital stay of 15 days. Sixty-eight percent of the patients had either a minor or major complication. Major complications included acute respiratory distress syndrome (n=2), intra-abdominal abscess (n=1), and pulmonary embolism (n=1). There were no deaths in our series. All patients demonstrated C-peptide and insulin production indicating graft function. Forty-one percent are insulin independent, and 27% required minimal amount of insulin or a sliding scale. All patients had preoperative pain and had been taking opioid analgesics; 82% no longer required analgesics postoperatively. Pancreatectomy with autologous islet cell transplantation can alleviate pain for patients with chronic pancreatitis and preserve endocrine function.

Adolescent↗
PubMed2003

Docosahexaenoic acid selectively augments muscarinic stimulation of epithelial Cl- secretion.

BACKGROUND: We investigated the effect of various fatty acids on electrogenic chloride secretion in T84 cells, a model for intestinal epithelium. MATERIALS AND METHODS: T84 intestinal epithelial cells grown on permeable supports were studied by conventional current-voltage clamping. Membrane lipids from T84 cells were extracted, transmethylated, and analyzed by gas chromatography. Lipid extracts were fractionated into nonpolar, free fatty acids, and phospholipids by amynopropil column chromatography. RESULTS: Docosahexaenoic acid (DHA) but not eicosapentanoic acid or other fatty acids selectively enhanced the secretory response to the muscarinic agonist carbachol but not the response to other Ca2+ agonists (histamine, thapsigargin, or ionomycin) or the response to the cAMP agonist forskolin. The ability of DHA to augment Cl- secretion appeared to correlate closer with free DHA levels than with membrane-bound DHA. Other effects of DHA on T84 cells included a reduction in transepithelial resistance (a measure of barrier function), actions that were dissociated from the effect on Cl- secretion. CONCLUSION: The results suggest that DHA, which has been shown to reverse organ pathology in experimental cystic fibrosis, may selectively affect agonist-regulated transport events and other fundamental properties of epithelial cells.

Carbachol↗
PubMed2003

Electrogenic ion transport in mammalian colon involves an ammonia-sensitive apical membrane K+ conductance.

It is remarkable that high ammonia concentrations can be present within the colonic lumen without compromising normal epithelial function. We investigated the impact of luminal ammonia on Cl- secretion in native tissue. Stripped human colonic mucosa and unstripped rat distal colon were used. Paired samples were mounted in modified Ussing chambers for electrophysiological studies. In rat distal colon, apical ammonia dose-dependently blocked forskolin-activated short-circuit current with an IC50 to approximately 5 mM. Basolateral NH4Cl was less effective. Luminal methylamine (50 mM), chromanol 293B (10-50 microM), and Ba2+ (5 mM) blocked cAMP-activated short-circuit current but apical clotrimazole (100 microM) was without effect. In stripped human colonic mucosa, luminal but not basolateral NH4Cl (10 mM) and luminal Ba2+ (5 mM) suppressed forskolin-activated short-circuit current. Ammonia may be an endogenous regulator of colonic water and salt secretion. Apical K+ channels may be involved in the regulation of cAMP-stimulated Cl- secretion in mammalian colon.

Ammonia↗
PubMed2003

Clinical trials of transplant tolerance: slow but steady progress.

The search for tolerance therapies that would thwart the alloimmune response following organ transplantation while preserving a patient's protective immune response has been a formidable goal for clinical immunologists. Over the past few decades, a more detailed understanding of the molecular events associated with T-cell recognition and activation has demonstrated the feasibility of various tolerance approaches, such as costimulation blockade, in numerous animal models of both autoimmunity and transplantation. Yet, only a few promising new therapies have reached the early stages of human clinical development. In contrast, the use of T-cell depleting induction therapy has become widespread, and new trials have been designed with immunosuppressive drug withdrawal in mind. Furthermore, nonmyeloablative mixed chimeric approaches have allowed complete immunosuppressive withdrawal in some limited cases. In the course of these investigations, however, what has become increasingly clear is that the distinctions between immunosuppression and tolerance have been blurred as the success and durability of the therapies rely as much on the state of the organ and organism as they do the mechanism of action of the drug. In this review, we provide a summary of the progress and lessons in promoting clinical transplant tolerance and an overview of promising agents.

Chimera↗
PubMed2003

Mucosal repair in the gastrointestinal tract.

OBJECTIVE: The epithelial response to injury in the intestinal mucosa will be described. DESIGN: A comprehensive evaluation of the literature was performed to provide a thorough review of mucosal injury and repair. RESULTS: The intestinal mucosa is a rapidly proliferating sheet of epithelial cells that sustains injury in response to stresses ranging from physiologic daily digestive trauma to severe insults associated with ischemia, chemicals, and infection. Breaks in epithelial continuity impair mucosal barrier function, perturb normal absorptive and secretory transport properties, and render the host susceptible to local infection and distant organ pathology. Minor breaches are rapidly repaired by epithelial restitution, a process independent of cell proliferation. Restitution is regulated by a variety of cytokines and growth factors and is modulated by integrin-dependent interactions with the extracellular matrix. The intracellular mechanisms that control restitution are complex and involve signaling pathways that control dynamic remodeling of the actin cytoskeleton. Emerging understanding of reparative processes suggest several possible therapeutic strategies to enhance gastrointestinal wound healing. CONCLUSION: Minor epithelial injuries are repaired with the complex process of epithelial restitution independent of cell proliferation.

Animals↗
PubMed2003

Increased biliary fistulas after liver resection with the harmonic scalpel.

The Harmonic Scalpel (HS) is frequently used for hepatic resection. Yet, no current study addresses its utility compared to conventional methods. We reviewed our experience with this device to determine if it decreased perioperative complications when compared to the traditional clamp crushing technique. One hundred forty-nine anatomic hepatic resections were performed at our institution from September 1992 to February 2002. Patients were divided into two groups based on the technique of resection: HS [53% (n = 79)] versus clamp crushing [47% (n = 70)]. Use of the HS was associated with a shorter mean operative time (357 +/- 15.0 vs. 404 +/- 19.1 min; p = 0.05) and a trend toward decreased blood loss (1211 +/- 125.5 vs. 1411 +/- 180.7 mL; P = NS) and transfusion requirements (2.6 +/- 0.5 vs. 1.7 +/- 0.3 units; P = 0.10). However, use of the HS was associated with a significant increase in biliary fistulas [24% (n = 19) vs. 7% (n = 5); P = 0.01]. Use of the Harmonic Scalpel was associated with decreased operative time and a trend toward decreased blood loss and transfusion requirements. Its use was also associated with a significant increase in the incidence of postoperative bile leaks, and, therefore, surgeons must be vigilant during liver parenchymal transection when using this device.

Adult↗
PubMed2002

Bryostatin-1 attenuates TNF-induced epithelial barrier dysfunction: role of novel PKC isozymes.

Tumor necrosis factor (TNF) increases epithelial permeability in many model systems. Protein kinase C (PKC) isozymes regulate epithelial barrier function and alter ligand-receptor interactions. We sought to define the impact of PKC on TNF-induced barrier dysfunction in T84 intestinal epithelia. TNF induced a dose- and time-dependent fall in transepithelial electrical resistance (TER) and an increase in [(3)H]mannitol flux. The TNF-induced fall in TER was not PKC mediated but was prevented by pretreatment with bryostatin-1, a PKC agonist. As demonstrated by a pattern of sensitivity to pharmacological inhibitors of PKC, this epithelial barrier preservation was mediated by novel PKC isozymes. Bryostatin-1 reduced TNF receptor (TNF-R1) surface availability, as demonstrated by radiolabeled TNF binding and cell surface biotinylation assays, and increased TNF-R1 receptor shedding. The pattern of sensitivity to isozyme-selective PKC inhibitors suggested that these effects were mediated by activation of PKC-epsilon. In addition, after bryostatin-1 treatment, PKC-delta and TNF-R1 became associated, as determined by mutual coimmunoprecipitation assay, which has been shown to lead to receptor desensitization in neutrophils. TNF-induced barrier dysfunction occurs independently of PKC, but selective modulation of novel PKC isozymes may regulate TNF-R1 signaling.

Antigens, CD↗
PubMed2002

Molecular regulation of Na+-K+-2Cl- cotransporter (NKCC1) and epithelial chloride secretion.

Defective regulation of epithelial secretion underlies the clinical manifestations of a number of important human diseases ranging from cystic fibrosis to secretory diarrhea. Although much attention has focused on the role of apical membrane chloride (Cl-) channels in this process, emerging evidence highlights the importance of a basolateral Na+-K+-2Cl- cotransporter (NKCC1) as an independent regulatory site that may determine the overall rate of epithelial secretion. The cotransporter NKCC1 is expressed not only in epithelial cells but also in virtually all mammalian cells, where it plays a more generalized role in cell volume homeostasis, cell ionic composition, and, possibly, the control of cell growth. Emerging molecular evidence indicates that NKCC1 function is regulated in the short and long term at the level of protein phosphorylation, membrane targeting, and gene expression. An improved understanding of NKCC1 may lead to new therapeutic approaches to secretory diarrhea as well as diverse clinical conditions in which cell ion composition is disturbed.

Animals↗
PubMed2002

Opposing effects of PKCalpha and PKCepsilon on basolateral membrane dynamics in intestinal epithelia.

PKC is a critical effector of plasma membrane dynamics, yet the mechanism and isoform-specific role of PKC are poorly understood. We recently showed that the phorbol ester PMA (100 nM) induces prompt activation of the novel isoform PKCepsilon followed by late activation of the conventional isoform PKCalpha in T84 intestinal epithelia. PMA also elicited biphasic effects on endocytosis, characterized by an initial stimulatory phase followed by an inhibitory phase. Activation of PKCepsilon was shown to be responsible for stimulation of basolateral endocytosis, but the role of PKCalpha was not defined. Here, we used detailed time-course analysis as well as selective activators and inhibitors of PKC isoforms to infer the action of PKCalpha on basolateral endocytosis. Inhibition of PKC by the selective conventional PKC inhibitor Gö-6976 (5 microM) completely blocked the late inhibitory phase and markedly prolonged the stimulatory phase of endocytosis measured by FITC-dextran uptake. The PKCepsilon-selective agonist carbachol (100 microM) induced prolonged stimulation of endocytosis devoid of an inhibitory phase. Actin disassembly caused by PMA was completely blocked by Gö-6850 but not by Gö-6976, implicating PKCepsilon as the key isoform responsible for actin disruption. The Ca2+ agonist thapsigargin (5 microM) induced early activation of PKC when added simultaneously with PMA. This early activation of PKCalpha blocked the ability of PMA to remodel basolateral F-actin and abolished the stimulatory phase of basolateral endocytosis. Activation of PKCalpha stabilizes F-actin and thereby opposes the effect of PKCepsilon on membrane remodeling in T84 cells.

Actins↗
PubMedDate not supplied

Diffuse pancreatic adenocarcinoma identified in an adult with annular pancreas.

Annular pancreas is a congenital anomaly resulting from malrotation of the pancreatic ventral bud. Although annular pancreas in the adult is rare, it may be recognized with increased frequency as a result of more liberal use of pancreatic imaging studies in patients with chronic abdominal pain and suspected chronic pancreatitis. Malignancy in the setting of annular pancreas is an uncommon event that has been reported previously but has almost always been related to the annular (ventral) segment. We report an interesting case in which pancreatic adenocarcinoma diffusely involving the dorsal (nonannular) segment presented in a middle-aged female patient. This unusual presentation points out the importance of considering neoplasia as part of the differential diagnosis and the possibility of pancreatic pathology in the dorsal, nonannular segment when there is no obvious duodenal or biliary obstruction involving the annular ventral segment.

Adenocarcinoma↗
PubMedDate not supplied

K+ channel inhibition accelerates intestinal epithelial cell wound healing.

Restitution is the process by which superficial interruptions in the gastrointestinal mucosa are repaired by the flattening and spreading of epithelial cells surrounding the damage. During this process, mucosal epithelial cells undergo extensive reshaping and cytoskeletal remodeling. K(+) channels, located primarily on the basolateral surface of gut epithelial cells, are central to both actin polymerization, via their control of membrane potential, and cell volume regulation. We questioned whether K(+) channels are involved in restitution using an in vitro model of intestinal epithelium, monolayers of the human colon carcinoma cell line T84. We report that pharmacologic K(+) channel inhibition accelerates wound healing in T84 cell monolayers. Both Ca(++)-dependent and constitutively active channels are involved, as indicated by the sensitivity to clotrimazole, charybdotoxin, and barium. The ability of clotrimazole to accelerate wound resealing was also observed in Caco-2 cell sheets. Pharmacologic stimulation of K(+) channel activity had no effect on the repair rate. Analysis of the resealing process by time lapse and confocal microscopy revealed that K(+) channel inhibitors abolished the initial wound retraction, briefly accelerated the repair rate, and altered the shape of the cell sheet abutting the injury during the early phase of resealing. We hypothesize that K(+) channel inactivation interrupts the coregulation of f-actin polymerization and volume control that is initiated by the healing process.

Barium↗