Drug-induced endocytosis of neonatal erythrocytes

The erythrocytes of the newborn infant have many properties that distinguish them from those of adults, and their membranes are also different from those of adult erythrocytes. We compared the ability of adult and neonatal RBCs to undergo endocytosis on exposure to drugs. Using a quantitative method, we showed that neonatal erythrocytes undergo a greater degree of endocytosis than do adult RBCs in response to primaquine, vinblastine, and chlorpromazine, and are sensitive to lower concentrations of the drugs. Some forms of drug-induced endocytosis are red cell age-dependent; when RBCs were separated by density gradient centrifugation, the membranes of the younger, less dense populations of both the neonatal and adult RBCs were capable of more extensive internalization than those of the denser, older RBCs. Neonatal RBCs of a given density undergo more endocytosis than do adult RBCs of the same density, suggesting that the membrane of the neonatal RBC is less stable and capable of more of the reorganization reflected in endocytosis than is the adult RBC membrane.     

Localization of the cystic fibrosis transmembrane conductance regulator in pancreas.

Cystic fibrosis (CF) is characterized by an abnormality in cAMP-regulated chloride transport that results from a primary defect in the protein product of the CF gene, the CF transmembrane conductance regulator (CFTR). In this report, antibodies against CFTR peptides were used to localize the CFTR protein in human pancreas. An affinity purified antibody (alpha-1468) raised against a synthetic CFTR peptide identified a 155-170-kD protein on immunoblot. Cytochemical studies with alpha-1468 localized CFTR to small branching, tubular structures. The same structures were recognized by two other antibodies raised against different regions of the CFTR molecule. To identify the cells being stained, double-label immunofluorescence studies were performed using alpha-1468 and a monoclonal antibody which stains pancreatic centroacinar and intralobular duct cells. Both antibodies localized to the same population of cells, with alpha-1468 being confined to the apical domain of these cells. No conclusive staining of acinar cells was evident. These findings suggest that proximal duct epithelial cells play a key role in the early events leading to pancreatic insufficiency in CF, and imply that apical chloride transport by these cells is essential for normal pancreatic secretory function.     

Myosin in adult and neonatal human erythrocyte membranes

The heavy chain of myosin can be detected in human red cell membranes by immunoblot analysis with antiplatelet myosin antibodies. Neonatal red cell membranes have more immunoreactive myosin than adult membranes. Membranes from young adult red cells contain more immunoreactive myosin than membranes from old adult red cells. In contrast, young and old neonatal red cells have equivalent mounts of myosin. Erythrocyte myosin is present in a membrane fraction enriched in integral membrane proteins but is not found in cytoskeletal preparations.     

Inhibition of protein phosphatase 1 decreases PTH secretion from isolated dispersed parathyroid cells.

To investigate the regulation of parathyroid hormone secretion by phosphatases we examined the effect of okadaic acid, a selective inhibitor of protein phosphatases (PP)-1 and -2A, on isolated, dispersed parathyroid cells. Okadaic acid inhibited secretion from intact bovine, intact human and streptolysin-O permeabilized bovine cells. Approximately 10(-6) M okadaic acid resulted in a 50% decrease in parathyroid hormone (PTH) secretion from both intact and permeabilized cells, consistent with PP-1 being the target of inhibition. Upon subcellular fractionation, PP-1 overlapped but was not identical to either PTH, a marker of the secretory granule, or Na+/K+-ATPase, a plasma membrane marker. In summary, PP-1 activity is involved in Ca2+-dependent but not basal PTH secretion.     

The aging process of human neonatal erythrocytes

The red blood cell population of the human newborn is more heterogeneous than that of adults. To characterize this heterogeneity, red cells were separated on Stractan gradients into populations according to their density and, therefore, generally according to their age. Lipid content, phospholipid asymmetry, osmotic fragility, and deformability were measured. With increasing density, osmotic resistance and deformability decreased to a greater extent in the neonatal than the adult red cell. There was a marked loss of surface area throughout the life span of the neonatal red cell which was not accompanied by a parallel loss of membrane lipid. This apparent discrepancy could be explained at least in part by internalization of membrane lipid as a result of endocytosis, a process shown to be present in even the densest neonatal red cells.