Active sodium and potassium transport in high potassium and low potassium sheep red cells

The kinetic characteristics of the ouabain-sensitive (Na + K) transport system (pump) of high potassium (HK) and low potassium (LK) sheep red cells have been investigated. In sodium medium, the curve relating pump rate to external K is sigmoid with half maximal stimulation (K_1/2) occurring at 3 mM for both cell types, the maximum pump rate in HK cells being about four times that in LK cells. In sodium-free media, both HK and LK pumps are adequately described by the Michaelis-Menten equation, but the K_1/2 for HK cells is 0.6 ± 0.1 mM K, while that for LK is 0.2 ± 0.05 mM K. When the internal Na and K content of the cells was varied by the PCMBS method, it was found that the pump rate of HK cells showed a gradual increase from zero at very low internal Na to a maximum when internal K was reduced to nearly zero (100% Na). In LK cells, on the other hand, no pump activity was detected if Na constituted less than 70% of the total (Na + K) in the cell. Increasing Na from 70 to nearly 100% of the internal cation composition, however, resulted in an exponential increase in pump rate in these cells to about ⅙ the maximum rate observed in HK cells. While changes in internal composition altered the pump rate at saturating concentrations of external K, it had no effect on the apparent affinity of the pumps for external K. These results lead us to conclude that the individual pump sites in the HK and LK sheep red cell membranes must be different. Moreover, we believe that these data contribute significantly to defining the types of mechanism which can account for the kinetic characteristics of (Na + K) transport in sheep red cells and perhaps in other systems.     

Increased frequency of 6-thioguanine-resistant lymphocytes in peripheral blood of workers employed in cyclophosphamide production

The frequency of 6-thioguanine-resistant peripheral blood lymphocytes has been determined by autoradiography in a control population and a population of cyclophosphamide-exposed individuals. The mean variant frequency in a non-exposed population was found to be 2.76 ± 1.48 × 10⁻⁵. Subpopulations of smokers and non-smokers revealed statistically significantt differences in the variant frequencies, i.e. 3.52 ± 1.55 × 10⁻⁵ and 2.07 ± 1.05 × 10⁻⁵ respectively. In 20 out of a total of 23 individuals employed in cyclophosphamide synthesis and manufacturing, the variant frequency of 6-thioguanine-resistant lymphocytes was found to be higher than the maximum individual frequency found in the control population. The mean variant frequency in the cyclophosphamide-exposed population was 13.64 ± 13.56 × 10⁻⁵, a statistically significant increase as compared to the mean control frequency. There was no correlation between variant frequency and duration of employment suggesting that this test reflects the actual exposure and not a cumulative effect.     

Genotoxic evaluation of workers employed in pesticide production

Pesticides are widely used throughout the world in agriculture to protect crops and in public health to control diseases. Nevertheless exposure to pesticides can represent a potential risk to humans. Pesticide manufacturing unit workers are prone to possible occupational pesticide exposure. Therefore, this study was performed to evaluate the genotoxic effect of pesticide exposure in these workers. In the present investigation 54 pesticide workers and an equal number of control subjects were assessed for genome damage in blood lymphocytes utilizing the chromosomal aberration analysis and the buccal epithelial cell by adopting the micronucleus test. The results suggested that pesticide workers had a significantly increased frequency of chromosomal aberrations when compared with controls (mean+/-S.D., 8.43+/-2.36 versus 3.32+/-1.26; P<0.05). Similarly, the pesticides exposed workers showed a significant increase in micronucleated cells compared with controls (1.24+/-0.72 versus 0.32+/-0.26; P<0.05). Analysis of variance revealed that occupational exposure to pesticides had a significant effect on frequency of micronuclei (P<0.05), whereas smoking, age, gender and alcohol consumption had no significant effect on genetic damage (P>0.05). However, no association was found between years of exposure, smoking, age, gender, alcohol consumption and higher levels of genetic damage as assessed by the chromosomal aberration assay (P>0.05). Our findings indicate that occupational exposure to pesticides could cause genome damage in somatic cells.