John F. White

Intestinal pathophysiology in autism.

Autism is a life-long developmental disorder affecting as many as 1 in 500 children. The causes for this profound disorder are largely unknown. Recent research has uncovered pathology in the gastrointestinal tract of autistic children. The pathology, reported to extend from the esophagus to the colon, is described here along with other studies pointing to a connection between diet and the severity of symptoms expressed in autism. The evidence that there is impaired intestinal permeability in autism is reviewed, and various theories are discussed by which a leaky gut could develop. Lastly, some possible ways in which impaired gastrointestinal function might influence brain function are discussed.

Bicarbonate-dependent chloride absorption in small intestine: Ion fluxes and intracellular chloride activities

SummaryProximal, stripped segments of small intestine from the urodeleAmphiuma were short-circuited in media containing Na+, Cl− and HCO3−. Under these conditions there was a large net absorption of Cl−, a small net absorption of Na+ and a residual flux (JNetR) consistent with HCO3− secretion. Net Cl− absorption correlated with the short-circuit current (Isc); net Na+ absorption correlated negatively withJNetR. Acetazolamide eliminated theIsc, lowered Cl− absorption by 50%, and reduced net Na+ absorption without alteringJNetR. Benzolamide inhibited theIsc without alteringJNetR. Benzolamide inhibited theIsc more rapidly when applied on the mucosal surface. Replacement of Na+ or HCO3− (and CO2) in the media eliminated theIsc, net Cl− absorption and the residual flux. Likewise, inclusion of the stilbene SITS in the serosal media eliminated theIsc, net Cl− absorption and the residual flux. The cytoplasmic activity of Cl− (acia) was determined with single and double-barreled microelectrodes. Theacia of villus absorptive cells in normal media was 21.0mm and in excess of that expected on the basis of electrochemical equilibrium of Cl− at the mucosal membrane. Active Cl− accumulation was also observed in the presence of acetazolamide but was eliminated upon replacement of media Na+ with choline. The mucosal membrane potential was depolarized upon replacement of media Na+. It is concluded that Cl− is actively absorbed into intestinal cells ofAmphiuma by an electrogenic process located in the mucosal membrane. Depending on the level of intracellular HCO3−, accumulated Cl− may diffuse passively back into the mucosal media or undergo exchange with bath HCO3− at the serosal membrane.

Inhibition of Na,K-ATPase and sodium pump by anticancer ether lipids and protein kinase C inhibitors ET-18-OCH3 and BM 41.440

The anticancer ether lipid analogs ET-18-OCH3 and BM 41.440 inhibited Na, K-ATPase in the purified rat brain membrane fragments, with a potency comparable to that of their inhibition of protein kinase C. They also inhibited Na,K-ATPase in the crude membrane fraction of HL60 cells. Kinetic analysis indicated that the lipids had a mode of action different from that of ouabain, a classic inhibitor of the ATPase. The lipids also blocked 22Na uptake in the inside-out membrane vesicles of human erythrocytes. It is suggested that Na,K-ATPase might represent an additional site with which certain protein kinase C inhibitors can interact to alter cellular activities.

Alterations in electrophysiology of isolated amphibian small intestine produced by removing the muscle layers

Isolated segments of Amphiuma small intestine bathed in chloride or sulfate buffer generate a greater short-circuit current and a larger change in current in response to galactose when the serosal muscle layers are stripped from the mucosa. Intact (unstripped) segments are not apparently anoxic since stripped segments exposed to serosal N2 for 3 h display normal short-circuit currents but a reduced potential response to galactose, while the presence of muscle layers tends to reduce the short-circuit current but does not alter the potential response to galactose. Bullfrog small intestine also generates greater short-circuit current following removal of the muscle layers. The enhancing effect of stripping appears to be related to removal of a resistance to ion flow across the tissue.

Modes of Cl− transport across the mucosal and serosal membranes of urodele intestinal cells

SummaryThe characteristics of Cl− movement across luminal and basolateral membranes ofAmphiuma intestinal absorptive cells were studied using Cl−-sensitive microelectrodes and tracer36Cl techniques. Intracellular Cl− activity (aCli) was unchanged when serosal Cl− was replaced; when luminal Cl− was replaced cell Cl− was rapidly lost. Accordingly, the steady stateaCli could be varied by changing the luminal [Cl]. As luminal [Cl] was raised from 1 to 86mM,aCli rose in a linear manner, the mucosal membrane hyperpolarized, and the transepithelial voltage became serosa negative. In contrast, the rate of Cl− transport from the cell into the serosal medium, measured as the SITS-inhibitable portion of the Cl− absorptive flux, attained a maximum whenaCli reached an apparent value of 17mm, indicating the presence of a saturable, serosal transport step. The stilbeneinsensitive absorptive flux was linear with luminal [Cl], suggestive of a paracellular route of movement. IntracellularaCl was near electrochemical equilibrium at all but the lowest values of luminal [Cl] after interference produced by other anions was taken into account.aCli was unaffected by Na replacement, removal of medium K, or elevation of medium HCO3−. Mucosae labeled with36Cl lost isotope into both luminal and serosal media at the same rate and from compartments of equal capacity. Lowering luminal [Cl] or addition of theophylline enhanced luminal Cl− efflux. It is concluded that a conductive Cl leak pathway is present in the luminal membrane. Serosal transfer is by a saturable, stilbene-inhibitable pathway. Luminal Cl− entry appears to be passive, but an electrogenic uptake cannot be discounted.

Electrogenic Cl- absorption by Amphiuma small intestine: dependence on serosal Na+ from tracer and Cl- microelectrode studies.

SummaryThe Na+ requirement for active, electrogenic Cl− absorption byAmphiuma small intestine was studied by tracer techniques and double-barreled Cl−-sensitive microelectrodes. Addition of Cl− to a Cl−-free medium bathingin vitro intestinal segments produced a saturable (Km=5.4mm) increase in shortcircuit current (Isc) which was inhibitable by 1mm SITS. The selectivity sequence for the anion-evoked current was Cl−=Br−>SCN−>NO3−>F−=I−. Current evoked by Cl− reached a maximum with increasing medium Na concentration (Km=12.4mm). Addition of Na+, as Na gluconate (10mm), to mucosal and serosal Na+-free media stimulated the Cl− current and simultaneously increased the absorptive Cl− flux (Jm→sCl) and net flux (JnetCl) without changing the secretory Cl− flux (Js→mCl). Addition of Na+ only to the serosal fluid stimulatedJm→sCl much more than Na+ addition only to the mucosal fluid in paired tissues. Serosal DIDS (1mm) blocked the stimulation. Serosal 10mm Tris gluconate or choline gluconate failed to stimulateJm→sCl. Intracellular Cl− activity (aCli) in villus epithelial cells was above electrochemical equilibrium indicating active Cl− uptake. Ouabain (1mm) eliminated Cl− accumulation and reduced the mucosal membrane potentialψm over 2 to 3 hr. In contrast, SITS had no effect on Cl− accumulation and hyperpolarized the mucosal membrane. Replacement of serosal Na+ with choline eliminated Cl− accumulation while replacement of mucosal Na+ had no effect. In conclusion by two independent methods active electrogenic Cl− absorption depends on serosal rather than mucosal Na+. It is concluded that Cl− enters the cell via a primary (rheogenic) transport mechanism. At the serosal membrane the Na+ gradient most likely energizes H+ export and regulates mucosal Cl− accumulation perhaps by influencing cell pH or HCO3− concentration.

Intestinal HCO3- secretion in Amphiuma: stimulation by mucosal Cl- and serosal Na+.

SummaryThe requirement for Na+ and Cl− in the bathing media to obtain a maximal HCO3− secretory flux (

Contribution of villus and intervillus epithelium to intestinal transmural potential difference and response to theophylline and sugar

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