Biomedical subjects

N Higgs

Publications and source records attributed to N Higgs.

4 recordsLinked to original sources

PubMed2000

Carbachol potentiates cholera toxin-induced secretion in a colonic epithelial cell line (HT29-19A) and rat ileal mucosa in vitro.

Recent studies show that enteric nerves are involved in the action of cholera toxin, both in vivo and in vitro. The aim of this study was to investigate in vitro the influence of carbachol, a cholinergic agonist, on the action of cholera toxin. Cultured HT29-19A cell lines and rat ileal mucosa were used in an Ussing chamber for the measurement of short-circuit current induced by cholera toxin. Cyclic AMP was measured from HT29-19A cell lines by standard radio-immunoassay. Pre-treatment of the HT29-19A cell lines with carbachol potentiated cholera toxin-induced secretory response, and enhanced accumulation of cAMP. Carbachol also potentiated the cholera toxin-secretory response in the rat ileal mucosa, but only following pretreatment with the prostaglandin synthesis inhibitor, indomethacin. There was synergistic interaction between cholera toxin and cholinergic neurotransmitter carbachol on the intestinal epithelium. Cholinergic agonists may play a role in regulating the secretory response to the toxin. Such interaction is masked in the intact tissues in vitro due to the release of prostaglandins during isolation.

Animals↗

PubMed1998

Identification of the second heparin-binding domain in human complement factor H.

Complement factor H (fH) regulates activation of the alternative pathway of C, reducing the amount of C3b deposited on sialic acid-rich surfaces. Heparin binding has been used as a model for examining the sialic acid-binding characteristics of fH. We have previously shown that of the 20 short consensus repeat (SCR) modules of fH, SCR 7 contains an important heparin binding site, but other SCRs also play a role in heparin binding. To localize the other sites, we prepared recombinant truncated and SCR deletion mutants of fH and tested them by heparin-agarose affinity chromatography. The 5 C-terminal SCRs were found to contain a heparin binding site as an SCR 7 deletion mutant of the N terminal 15 SCRs did not bind heparin, but a construct consisting of SCRs 16-20 was shown to bind heparin. Double deletion of SCRs 7 and 20 from fH abrogated binding to heparin, indicating that SCR 20 contains a heparin binding site. This finding was confirmed with the observation that attachment of SCR 20 to a group of nonbinding SCRs produced a heparin-binding protein. A protein consisting of SCRs 19 and 20 did not bind heparin, whereas SCRs 18-20 did, indicating that, although SCR 20 contains a heparin binding site, at least two nonspecific adjacent SCRs are required. fH-related protein-3 (FHR-3) possesses an SCR homologous to SCR 7 of fH and bound heparin, whereas FHR-4, which lacks such an SCR, did not. Thus, fH contains two separate heparin binding sites, which are located in SCRs 7 and 20.

Apolipoproteins↗

PubMed1990

Cellular basis for defective electrolyte transport in inflamed human colon.

Electrolyte transport pathways in distal colonic mucosa from patients with noninflammatory and inflammatory (ulcerative colitis, Crohn's colitis) disease of the large bowel were studied in vitro with electrophysiological techniques. Noninflamed tissues exhibited substantial amiloride-sensitive electrogenic sodium transport. In contrast, inflamed but structurally intact tissues exhibited only a modest degree of electrogenic sodium transport, significant increases in total tissue conductance and apical membrane conductance, and a 100% increase in the arachidonic acid content of the cell membrane fraction of mucosal homogenates. Replacement of chloride with gluconate decreased total tissue conductance to a greater extent in inflamed than in noninflamed tissues, and total tissue conductance was higher in inflamed than in noninflamed tissues in the presence of transepithelial potassium and sodium gradients, suggesting enhanced mucosal "leakiness" to anions and cations in acute colitis. Apical addition of nystatin virtually abolished amiloride-sensitive apical sodium uptake in both groups, indicating that the ionophore formed channels in the apical membrane of noninflamed and diseased mucosa. Additional studies showed that mucosal inflammation decreased maximal activity of the basolateral sodium pump by 76%. Thus, defects in the biophysical properties of colonic epithelial cell membranes are likely to be important factors in the pathogenesis of diarrhea in ulcerative and Crohn's colitis.

Adult↗

PubMed1984

Influence of morphine tolerance and withdrawal on intestinal salt and water transport in the rat in vivo and in vitro.

Intestinal water and electrolyte transport was investigated in vivo and in vitro in rats made tolerant to morphine and subsequently withdrawn with naloxone. Rats were rendered tolerant by injection of a slow-release emulsion containing morphine (75 mg/rat over 48 h), and when challenged with naloxone, they exhibited a characteristic withdrawal syndrome that included acute diarrhea. Morphine tolerance did not influence water absorption from ileal or colonic loops in vivo but naloxone-induced withdrawal provoked a rapid and sustained reduction in absorption. Naloxone did not affect absorption in control animals. In further experiments, sodium and chloride fluxes were measured in isolated stripped ileal mucosa derived from animals made tolerant to morphine and withdrawn with naloxone. Net sodium and chloride absorption was markedly reduced in mucosa derived from withdrawn animals compared with that derived from tolerant animals (Na+: 1.12 +/- 0.76 vs. 5.52 +/- 0.46, and Cl-: 0.60 +/- 0.52 vs. 4.70 +/- 0.80 microEq/cm2 X h, in withdrawn and tolerant animals, respectively; n = 8; p less than 0.001 and p less than 0.005). When an attempt was made to induce withdrawal by adding naloxone in vitro to isolated mucosa derived from tolerant animals, no effect on transport was detected whether the mucosa was stripped of muscle layers or not. Thus naloxone had to be given in vivo to produce withdrawal effects in mucosa studied subsequently in vitro. Naloxone also had an effect in control rats when a 50% reduction in net chloride absorption was observed in isolated ileal mucosa derived from these animals. Net sodium absorption was unaffected. These data support a role for endogenous opiates in the control of intestinal transport and provide a mechanism for the diarrhea associated with opiate withdrawal.

Animals↗