Chelator-mediated iron efflux from reticulocytes

The mechanism by which bipyridine and phenanthroline types of iron chelator inhibit iron uptake from transferrin and iron efflux mediated by pyridoxal isonicotinoyl hydrazone was investigated using rabbit reticulocytes with the aim of providing more information on the normal process of iron uptake by developing erythroid cells. It was shown that the chelators block cellular uptake by chelating the iron immediately after release from transferrin while it is still in the membrane fraction of the cells. The iron-chelator is then released from the cells by a process which is very similar to that of transferrin release with respect to kinetics and sensitivity to incubation temperature and the effects of metabolic inhibitors and other chemical reagents. These results are compatible with the conclusion that both transferrin and the iron-chelators in the cells are mainly present in endocytotic vesicles and are released from the cells by exocytosis. The chelators were also shown to block the pyridoxal isonicotinoyl hydrazone-mediated efflux of iron from cells which had taken up iron in the presence of isoniazid, an inhibitor of haem synthesis, by chelating the iron in the cytosol and the mitochondria. In this case, the iron-chelator complexes were not released from the cells. Measurement of the diethyl ether/water partition coefficients of bipyridine and 1,10-phenanthroline and their iron complexes gave much higher values for the free chelators, supporting the concept that the chelators trap the iron intracellularly because of differences in the lipid solubility and, hence, membrane permeability to the free chelators and their iron complexes.     

Age-related changes in the control of hepatic cyclic AMP levels by alpha 1- and beta 2-adrenergic receptors in male rats

Hepatocytes from juvenile male rats (80-110 g) showed a 12-fold elevation of cAMP in response to epinephrine, which was mediated by beta 2-adrenergic receptors. In these cells, either alpha 1- or beta 2-adrenergic stimulation alone activated phosphorylase and glucose release although the alpha 1-phosphorylase response was 10-fold more sensitive to epinephrine and resulted in more rapid (by 10-20 s) activation of the enzyme. This suggests that the beta 2-adrenergic response is functionally unimportant for glycogenolysis, even in juvenile rats. beta 2-Adrenergic stimulation did, however, produce an increase in the rate of gluconeogenesis from [U-14C] lactate in these cells. Aging in the male rat was associated with attenuation of the beta 2-adrenergic cAMP response coupled with the emergence of an alpha 1-receptor-mediated accumulation of cAMP. The order of potency displayed by the alpha 1-adrenergic/cAMP system to adrenergic agonists and antagonists was identical with that of the alpha 1-adrenergic/Ca2+ system. These data suggest that, in maturity, hepatic alpha 1-receptors become linked to 2 separate transduction mechanisms, namely Ca2+ mobilization and cAMP generation. Calcium depletion of hepatocytes from adult, but not juvenile, male rats increased the alpha 1-component of the cAMP response to epinephrine, but under these conditions, alpha 1-activation of phosphorylase occurred more slowly than in calcium-replete cells. Blockade of alpha 2-adrenergic receptors did not significantly modify catecholamine effects on hepatocyte cAMP or phosphorylase a levels in male rats at any age studied, suggesting a lack of functional significance for these receptors in the regulation of glycogenolysis.     

THE EFFECT OF INSULIN, ALLOXAN DIABETES, AND ANOXIA ON THE ULTRASTRUCTURE OF THE RAT HEART

Hearts from normal and alloxan diabetic rats were perfused in vitro with a bicarbonate-buffered medium containing glucose. Transport of glucose through the cell membrane was stimulated with insulin or by induction of anaerobiosis. The organs were rapidly fixed and examined by electron microscopy. Transport stimulation was not associated with any increase in the number of sarcolemmal invaginations or subsarcolemmal cytoplasmic vesicles. It was concluded that glucose transport and the effects of insulin or anoxia do not involve pinocytosis. The relationship of pinocytosis to glucose transport is discussed. The appearance of numerous lipid inclusions at the Z line level of the sarcomeres in the diabetic and anoxic myocardia is described.