The transport of the lead cation across the intestinal membrane

Abstract

1. The transport of the lead cation has been investigated using the everted sac preparation of Wilson & Wiseman (1954). 2. Only a small percentage of lead was transported into the serosal compartment but there was a rapid and massive uptake onto the tissue. There was no significant difference in the amount of lead cations transported across different regions of the small intestine. 3. Both the rate of transport into the serosal compartment and the tissue uptake increased linearly with increasing concentration of the lead cation, from 10−7 M to 5 × 10−5 M. Little evidence for saturation of serosal transport or tissue uptake was found. 4. Lead transport into the serosal compartment appeared to be related to water movement, but was little affected by changes in glucose concentration and temperature. 5. It is concluded that lead is transported into the serosal space by a process of passive diffusion linked to water transport. 6. The interaction between lead ions and the intestinal tissue was extremely tenacious and displayed characteristics of covalent bonding. 7. It is suggested that the lead cation interacts with tissue phosphate ions thus removing lead ions from the transport pool. Chelation of lead to form a neutral species reduces this interaction and also promotes transport.

Gastro-Intestinal Absorption of Lead in Children and Adults: Overview of Biological and Biophysico-Chemical Aspects

“…In other studies experimental artifacts, such as the use of medium cofactors that remove lead by precipitation, limit conclusions to be drawn about regional uptake in the small intestine (e.g. Blair et at., 1979;Gruden and Stantic, 1975). Hussein and coworkers (1984) have found that lumenal lead dosing ot isolated loops of guinea-pig colon and jejunum yields significant lead uptake at both sites, but colonic uptake is less than that in jejunal epithelium.…”

Factors controlling lead bioavailability in the Butte mining district, Montana, USA

“…However, the assumption that the bioavailability determined using Pb forms representative of a smelter site may be applied to assessing soils impacted by mining and milling waste is incorrect, because solid phases in mining soils are typically much less soluble than the oxidised Pb compounds emitted from active smelters (Griffin, 1991). The dissolution rate of Pb-bearing minerals in the GI tract is also a factor limiting bioavailability, because Pb absorption occurs primarily from the fluid phase in the small intestine (Blair et al, 1979;Conrad and Barton, 1978). Therefore, differences inherent between mine waste and smelter-derived Pb dissolution rates may result in an overestimate of Pb bioavailability if the results of studies using smelter materials are used as analogues for mine-waste-impacted soils.…”

Effect of dietary and synthetic chelating agents on the intestinal absorption of lead

“…The remainder of the small intestine was removed by severing at the ileocaecal junction. Regions of the duodenum, jejunum and ileum were selected as described by Blair et al, 1 and everted sacs prepared as described by Wilson and Wiseman. 4 Each sac was filled with 500 fil Krebs-Henseleit bicarbonate buffer 5 and incubated for 30 min.…”