Active transport of lead by human red blood cells

Abstract

Human red cells suspended in lead‐citrate buffers (2.6μM Pb2+) take up much less Pb than predicted from studies of equilibrium binding of Pb to haemolysates. Pb uptake is increased by ATP depletion, or by loading at 0°C. Tracer studies with 203Pb indicate that the low uptake at 37°C in the presence of substrate is not due to membrane impermeability to Pb. Cold‐loaded cells extrude Pb against a concentration gradient at 37°C when glucose is present. These results suggest that the cellular loading of Pb is dependent on the balance between an inward leak and an outward pump. The extrusion of Pb from the cells is possibly brought by the Ca pump.

Passive transport and binding of lead by human red blood cells.

“…This would not be enough to reach a ratio of 99:1 between red cells and plasma. On the other hand, there is evidence that Pb is actively extruded from red cells (Simons, 1984). The mechanism has not been characterized in detail, and the pumping rate under physiological conditions is unknown.…”

“…7 shows there is little difference between the batches of cells when Pb uptake is measured in the usual way. A very different picture emerges when the cells are centrifuged through silicone oil, a procedure which measures precipitated and cell-attached Pb3(PO4)2 as well as intracellular Pb (Simons, 1984). Phosphate leaves the cells down its concentration gradient, and precipitates as Pb3(PO4)2 in a time-and concentration-dependent manner.…”

“…Earlier studies of Pb transport have shown that it is rapidly taken up by red cells (Bambach, Kehoe & Logan, 1942;Mortensen & Kellogg, 1944;Clarkson & Kench, 1958 Evidence for the active transport of Pb out of red blood cells has been published already (Simons, 1984). This work is mainly concerned with the passive transport of Pb across the cell membrane.…”

“…The cells were resuspended in the same medium, and their Pb content measured as described below. This washing procedure removes any Pb3(PO4)2 precipitated with the cells, or adhering to their surface (Simons, 1984), although the formation of Pb3(PO4)2 was in any case minimized by pre-incubation with inosine. An insignificant amount of Pb would have been lost from the cells during washing, because of its slow efflux at 40 (Simons, 1984, and Fig.…”

“…The majority of experiments used cells which had been metabolically depleted in order to overcome the active extrusion of Pb which occurs in the presence of glucose (Simons, 1984). To achieve depletion, cells were normally pre-incubated with 5 mM-inosine and 5 mM-iodoacetamide for 2 h. Fig.…”