Chemical modification of the Na+/H+ exchanger of thymic lymphocytes. Inhibition by N-ethylmaleimide

A Na+/H+ exchanger is involved in the regulation of cytoplasmic pH and cellular volume in a variety of cells. Little is known about the molecular nature of this exchanger. The purpose of this study was to survey a variety of group-specific covalent reagents as potential inhibitors of the exchanger. Na+/H+ countertransport activity was assayed as the amiloride-sensitive rate of Na+-induced alkalinization in acid-loaded lymphocytes, or as the rate of swelling in cells suspended in sodium propionate medium. Activity was not affected by proteinases or by carboxyl-group and amino-group specific reagents. A significant inhibition was produced by diethylpyrocarbonate, a histidine-specific reagent and by N-ethylmaleimide, a sulfhydryl group reagent. A similarly reactive but nonpermeating sulfhydryl agent, glutathione-maleimide, failed to inhibit Na+-H+ exchange. Moreover, the reaction with N-ethylmaleimide was sensitive to changes in the cytoplasmic pH. The data suggest that the chemically reactive groups of the Na+/H+ exchanger of lymphocytes have limited exposure to the extracellular medium but that an internally located sulfhydryl group is critical for the cation-exchange activity.     

Effect of cortisol, its polymeric derivative and adenylate cyclase activators on the content of cyclic AMP in rat thymocytes

In has been shown that cortisol immobilized on polyvinylpyrrolidone (PVP-GC) affects cyclic AMP production stimulated by adenosine and isoproterenol in rat thymocytes. This effect of PVP-GC is specific for cortisol: antiglucocorticoid progesterone (at a concentration of 10(-5) M) inhibited completely the action of PVP-GC on the intracellular cAMP level. It is suggested that cortisol effect on cAMP production is one of the mechanisms of glucocorticoid hormone action in target cells.     

Superoxide perturbation of the organization of vascular endothelial cell membranes

Cultured porcine thoracic aorta endothelial cells were covalently labeled with 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance spectrometry revealed two major binding environments representing strongly and weakly immobilized species. The disorder parameter of weak/strong, determined from the respective peak amplitudes, was irreversibly elevated following incubation of endothelial cells with a superoxide-generating system, indicating increased membrane fluidity. The rate of increase in membrane disorder was dependent upon superoxide generation rates. Incorporation of the spin-label at concentrations less than 250 microM had no effect on cell viability. The cellular proteins reacting with the spin-label were predominantly membrane proteins, characterized by immunoblotting using a rabbit anti-4-maleimido-2,2,6,6-tetramethylpiperidinooxyl IgG, following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophorectic transfer to nitrocellulose.     

Induced maternal behavior in the domestic hen. Influence of partial or total separation on the maintenance of maternal responsiveness

The influence of direct physical contact on maintaining maternal responsiveness in induced adult hens was investigated using a separation procedure. Partial separation from chicks causes a significant decline of the clucking rate in hens, this response however does not disappear as in the case of total separation. The possibility for physical contact between hen and chicks contributes largely, but not uniquely, to maintain maternal responsiveness in the domestic hen.     

Growth-dependent expression of a cell surface glycoprotein

The expression of the hepatocellular membrane receptor for desialylated galactose-termining glycoproteins was studied during different proliferative stages of a human hepatoma cell line. Rapidly growing cells exhibited a reduced endocytotic rate of desialylated orsomucoid as compared to non-growing cells. This reduction was shown to be the consequence of a lower concentration of active cell-surface associated receptor protein in the dividing cells.