Patrizia Baldini

Insulin effect in vitro on human erythrocyte plasma membrane

The effect of porcine insulin has been tested in vitro on human erythrocyte plasma membrane (Na+−K+) and Mg2+-ATPase activities as well as on membrane fluidity. The results indicate that the hormonal treatment significantly inhibits (Na+−K+)-ATPase activity, and at the same time decreases membrane fluidity.

Influence of Pertussis toxin on CD1a Isoform Expression in Human Dendritic Cells

Pertussis toxin (PTX) is an exotoxin produced by Bordetella pertussis. It is known to exert adjuvant activities inducing Th1-launched immune responses. In this study, we show that PTX can selectively block the expression of CD1a isoform during the differentiation of human monocytes into dendritic cells. In fact, dendritic cells differentiated from monocytes in the presence of PTX do not express CD1a on their surface, unlike CD1b and CD1c isoforms, which are normally regulated. The impaired CD1a expression on cell membrane depends, at least partially, on decreased mRNA transcription and does not affect cellular capability to respond to other maturation stimuli. Since CD1a+ dendritic cells are involved in the early steps of primary immune response, the interference of PTX in the CD1a expression may be relevant for its employment as adjuvant.

Insulin binding and internalization in rat hepatocytes during prenatal and postnatal life.

Insulin binding to isolated rat hepatocytes was studied during prenatal and postnatal life. Results show that in hepatocytes isolated from prenatal, postnatal and adult rat there is a constant increase in the number of insulin binding sites per cell, whereas the affinity of plasma membrane receptors for the hormonal ligand remains unaltered from prenatal to adult hepatocytes. Autoradiographic studies indicate a greater internalization of hormone during prenatal life and, taking into account the increase of cell size, suggest an unchanged surface density of receptor sites before and after birth.

Effect of colchicine on rat liver plasma membrane.

Colchicine effect has been tested on rat liver plasma membrane-bound enzymes after in vitro or in vivo treatment. It appears that the in vitro treatment does not affect 5-nucleotidase, Mg2+-ATPase and (Na+ + K+)-ATPase, whereas adenylate cyclase is sensitive to both in vitro and in vivo treatment, the latter condition being also effective for 5-nucleotidase.

Effect of chlorpropamide and phenformin on rat liver: the effect on plasma membrane-bound enzymes and cyclic AMP content of hepatocytes in vitro.

Chlorpropamide and phenformin inhibited (Na+ - K+)-ATPase and stimulated a high affinity cyclic AMP-phosphodiesterase of isolated liver plasma membrane when tested in vitro. In addition, the two drugs decreased the intracellular cyclic AMP content of isolated hepatocytes without being effective on plasma membrane-bound adenylate cyclase. The results suggest that the plasma membrane plays an important role in the mechanism of action of the two hypoglycemic drugs, but do not exclude the presence of intracellular targets.

Tyrosine aminotransferase activity of frog (Rana esculenta) liver—III. A circannual study

A circannual study of tyrosine aminotransferase and other metabolic enzymes in frog liver is reported. The subcellular distribution of all enzymatic activities under investigation was also studied. Results show significant oscillations of all enzymatic activities throughout the year; in particular tyrosine aminotransferase has a marked summer maximum. The subcellular distribution of tyrosine aminotransferase shows significant variations: the soluble activity of the enzyme presents a bimodal circannual distribution, which has its counterpart in an increased activity of heavier fractions.

Hypoglycemic drugs increase liver plasma membrane microviscosity in vitro

The effect of hypoglycemic drugs chlorpropamide and phenformin has been tested on isolated liver plasma membranes as to their microviscosity parameters. Results reported suggest that both drugs are able to increase in vitro plasma membrane microviscosity in a dose-dependent way.

Tyrosine aminotransferase activity of frog (Rana esculenta) liver. II: Comparative aspects of intracellular distribution.

1. A subcellular fractionation procedure for frog liver is reported and validated by the distribution pattern of several marker enzymes, also in comparison with rat liver. 2. The subcellular distribution of tyrosine aminotransferase was investigated in frog liver as compared to rat liver: a different distribution of the enzyme was observed, being the activity mostly recovered in mitochondrial and cytosolic compartments. 3. Results indicate that mitochondrial tyrosine aminotransferase of both frog and rat liver is a matrix enzyme, even if differences are observed concerning its release from the organelles upon detergent treatment.