Effect of treatment with cadmium on kinetic properties of Na+, K+-ATPase and glucose-6-phosphatase activity in rat liver microsomes: A correlative study on influence of lipid/phospholipid make-up

Studies on Cd hepatotoxicity have focused mainly on induction of cytochrome P450 system and related enzymes. In the present study young adult male rats given a single intra-peritoneal injection of Cd (0.84 mg Cd/kg body weight) and effects on kinetic parameters rat liver microsomal Na+, K+-ATPase and G6Pase were evaluated at the end of 1 month and 1 week. The substrate and temperature kinetics parameters were examined and attempts were made to seek correlation with changes in lipid/phospholipid profiles. The Na+, K+ ATPase activity decreased only in 1 week Cd-treated group but recovered at the end of 1 month. The activity resolved in two distinct kinetic components in control as well as the experimental groups. In 1 week Cd-treated group the Km value of both the components was unchanged, whereas Vmax value decreased. In 1-month Cd-treated group Vmax value only of component I increased. The catalytic efficiency of both the components was not affected in the experimental groups. In 1-week Cd-treated group the energy of activations at high-temperature range (EH) and low-temperature range (EL) decreased, whereas for 1-month Cd-treated group the energies of activations did not change. The G6Pase activity measured at 37 °C was high only in 1-month Cd-treated group. The activity resolved in two kinetically distinguishable components in control as well as in the experimental groups. Km value of component I decreased in both the Cd-treated groups. In 1-month Cd-treated group the Vmax value of component II increased. The catalytic efficiency of G6Pase was unchanged despite changes in Km and Vmax. In 1-week Cd-treated group the EH and EL decreased, whereas only EL showed decrease in 1-month Cd-treated group. Cholesterol (CHL) content increased in both the Cd-treated groups. Content of lysophospholipid (Lyso), spinghomyelin (SPM) and phosphatidic acid (PA) increased, whereas phosphatidylcholine (PC) and phosphatidylserine (PS) decreased in 1-week Cd-treated group. In 1-month Cd group the Lyso, SPM, and PC increased while PC, phosphatidylethanolamine (PE) and PA decreased. In conclusion, Cd has short-term effects on microsomal Na+, K+-ATPase which are reversed by the end of 1 month and that G6Pase does not seem to be a target of Cd insult.