Na⁺/K⁺-ATPase Activity of Erythrocyte Membranes

Distribution of lead-203 in human peripheral blood in vitro.

“…This polypeptide has a molecular weight of about 82 000 to 85 000 and represents about 20% of the total membrane protein26 and is known to have a high content of protein sulphydryl (SH) groups.27 Therefore the binding of 203Pb to this band is not surprising, as lead has been shown to react with sulphydryl groups. Furthermore, it has been suggested that this polypeptide spans and penetrates the membrane, and thus may participate in ion transportation.2' Recently, this polypeptide was reported to contain a phosphorylated intermediate of Na+/K+-ATPase.28 If this is the case it may in part explain the mechanism by which lead inhibits Na+/K+-stimulated adenosine triphosphatase.29 30 In the present investigation membrane proteins were separated by polyacrylamide gel electrophoresis, and the results suggested that 203Pb is attached to high molecular weight polypeptides (MWt 130 000-230 000). This finding confirms our earlier observation, when erythrocyte membrane proteins were separated by gel chromatography."…”

Comparison of in vivo effect of inorganic lead and cadmium on glutathione reductase system and delta-aminolevulinate dehydratase in human erythrocytes.

“…Lead-induced shortening of the life-span of mature erythrocytes has been studied in vivo and in vitro by investigating alterations in membrane properties, for example, changes in permeability to K+ (Hemberg, 1967;Passow, 1970;Secchi, Alessio, and Cambiaghi, 1973) and in mechanical and osmotic fragility (Waldron, 1966). The presence of free membrane sulphydryl groups (Jacob and Jandl, 1962a, b) and a relatively high endogenous GSH level (Prins and Loos, 1969) have been clearly demonstrated to be indispensable for the structural and functional integrity of erythrocytes.…”

Dose-response relationships for inorganic lead

“…Lead affects the erythrocyte membrane In exposed workers, some of them with clinical intoxication, Hernberg ( 1970) described decreased Na+-K+-AT Pase activity; no correlation existed with conventional haematological parameters (e g. Pb B); this lack of correlation was thought to be due to effect of Pb on developing cells in bone marrow and not in peripheral blood There did not exist conclusive evidence of increased K+ turnover from the erythrocytes; active transport was unaffected even though activity of Na+-K+-AT Pase apparently was partly inhibited There existed a wide range of variation in this enzyme activity Secchi et al ( 1973) studied this enzyme in critical population groups, not occupationally exposed to Pb: in males with Pb B = 38 ± 10 ig/ they found a decreased Na+-K+-AT Pase activity if compared with a group with Pb B = 32 ± 8 2 (n = 26) From the individual data of this study (received by personal communication) the author calculated the percentage of subjects with < 40 vmol P/hr/mg tyrosine as indicator of decreased Na+-K+-AT Pase activity (Table 6) The D-R-relationship is given in Fig 4. In this study by Secchi et al in critical population groups living in Miland (Italy) Pb B levels are high if compared to levels as reported from other Western-European and American cities If Pb B determination had provided too high values because of faulty techniques, the D-R-curve would even shift to lower Pb B levels The coefficient of correlation between Pb B and Na+-K+-AT Pase activity was rather small (r = -0.37); sensitivity and specificity apparently is poor Up till now this study presents the only indication that at rather low levels of Pb B (< 30 g/100 ml) about 50 % of subjects already had a moderate inhibition; the slope of the curve is small; subjects with Pb B < 20 g/100 ml already had an inhibition in 15-20 % of cases One has to await for confirmation in more studies, before the health significance can be evaluated. The Finnish group also studied oxydative degradation: increase of glucose consumption; the average life span of erythrocytes decreased from 120 to 101 days in heavily exposed workers with Pb B = 59-162 g/100 ml; the degree of shortening correlated best with that of reticulocytosis, but also with anaemia, CPU, Pb B (Hernberg et al , 1967) The no-response level for these parameters probably is > 50 g/100 ml (Hernberg, 1974, personal communication).…”