PubMed Health⌕ Search

Biomedical subjects

H Sterling

Publications and source records attributed to H Sterling.

8 recordsLinked to original sources
PubMed2000

Regulation of ROMK1 channels by protein-tyrosine kinase and -tyrosine phosphatase.

We have used the two-electrode voltage clamp technique and the patch clamp technique to investigate the regulation of ROMK1 channels by protein-tyrosine phosphatase (PTP) and protein-tyrosine kinase (PTK) in oocytes coexpressing ROMK1 and cSrc. Western blot analysis detected the presence of the endogenous PTP-1D isoform in the oocytes. Addition of phenylarsine oxide (PAO), an inhibitor of PTP, reversibly reduced K(+) current by 55% in oocytes coinjected with ROMK1 and cSrc. In contrast, PAO had no significant effect on K(+) current in oocytes injected with ROMK1 alone. Moreover, application of herbimycin A, an inhibitor of PTK, increased K(+) current by 120% and completely abolished the effect of PAO in oocytes coexpressing ROMK1 and cSrc. The effects of herbimycin A and PAO were absent in oocytes expressing the ROMK1 mutant R1Y337A in which the tyrosine residue at position 337 was mutated to alanine. However, addition of exogenous cSrc had no significant effect on the activity of ROMK1 channels in inside-out patches. Moreover, the effect of PAO was completely abolished by treatment of oocytes with 20% sucrose and 250 microg/ml concanavalin A, agents that inhibit the endocytosis of ROMK1 channels. Furthermore, the effect of herbimycin A is absent in the oocytes pretreated with either colchicine, an inhibitor of microtubules, or taxol, an agent that freezes microtubules. We conclude that PTP and PTK play an important role in regulating ROMK1 channels. Inhibiting PTP increases the internalization of ROMK1 channels, whereas blocking PTK stimulates the insertion of ROMK1 channels.

Alanine↗
PubMed2000

CD47, a ligand for the macrophage fusion receptor, participates in macrophage multinucleation.

The macrophage fusion receptor (MFR), also called P84/BIT/SIRPalpha/SHPS-1, is a transmembrane glycoprotein that belongs to the superfamily of immunoglobulins. Previously, we showed that MFR expression is highly induced at the onset of fusion in macrophages, and that MFR appears to play a role in macrophage-macrophage adhesion/fusion leading to multinucleation. The recent finding that IAP/CD47 acts as a ligand for MFR led us to hypothesize that it interacts with CD47 at the onset of cell-cell fusion. CD47 is a transmembrane glycoprotein, which, like MFR, belongs to the superfamily of immunoglobulins. We show that macrophages express the hemopoietic form of CD47, the expression of which is induced at the onset of fusion, but to a lower level than MFR. A glutathione S-transferase CD47 fusion protein engineered to contain the extracellular domain of CD47, binds macrophages, associates with MFR, and prevents multinucleation. CD47 and MFR associate via their amino-terminal immunoglobulin variable domain. Of the nine monoclonal antibodies raised against the extracellular domain of CD47, three block fusion, as well as MFR-CD47 interaction, whereas the others have no effect. Together, these data suggest that CD47 is involved in macrophage multinucleation by virtue of interacting with MFR during adhesion/fusion.

Animals↗
PubMed1998

CD44 occupancy prevents macrophage multinucleation.

Cells of the mononuclear phagocyte lineage have the capability to adhere to and fuse with each other and to differentiate into osteoclasts and giant cells. To investigate the macrophage adhesion/fusion mechanism, we focused our attention on CD44, a surface glycoprotein known to play a role in hematopoietic cell-cell adhesion. We report that CD44 expression by macrophages is highly and transiently induced by fusogenic conditions both in vitro and in vivo. We show that CD44 ligands, hyaluronic acid, chondroitin sulfates, and osteopontin prevent macrophage multinucleation. In addition, we report that the recombinant extracellular domain of CD44 binds fusing macrophages and prevents multinucleation in vitro. These data suggest that CD44 may control the mononucleated status of macrophages in tissues by virtue of mediating cell-cell interaction.

Animals↗
PubMed1998

MFR, a putative receptor mediating the fusion of macrophages.

We had previously identified a macrophage surface protein whose expression is highly induced, transient, and specific, as it is restricted to actively fusing macrophages in vitro and in vivo. This protein is recognized by monoclonal antibodies that block macrophage fusion. We have now purified this protein and cloned its corresponding cDNA. This protein belongs to the superfamily of immunoglobulins and is similar to immune antigen receptors such as the T-cell receptor, B-cell receptor, and viral receptors such as CD4. We have therefore named this protein macrophage fusion receptor (MFR). We show that the extracellular domain of MFR prevents fusion of macrophages in vitro and therefore propose that MFR belongs to the fusion machinery of macrophages. MFR is identical to SHPS-1 and BIT and is a homologue of P84, SIRPalpha, and MyD-1, all of which have been recently cloned and implicated in cell signaling and cell-cell interaction events.

Amino Acid Sequence↗
PubMed1993

Effect of adenosine on heart rate in isolated muskrat and guinea pig hearts.

The purpose of this study was to compare the responses of isolated hearts of the diving muskrat with the nondividing guinea pig (GP) to determine the contribution of adenosine (ADO) to the profound bradycardia that was seen in isolated muskrat hearts during exposure to hypoxia. Muskrat hearts were more sensitive than GP hearts to the heart rate-lowering effects of exogenously applied ADO or a stable ADO analogue, (R)-N6-(phenylisopropyl)adenosine. The hearts of both species were unpaced, and the bradycardia appeared to be due to high degree of atrioventricular block. Radioligand binding with 8-cyclopentyl-1,3-[3H]dipropylxanthine to A1-ADO receptors was greater in cardiac membranes prepared from GP hearts than from muskrat hearts. Nucleoside transporter antagonist binding was also greater in GP hearts compared with muskrats. This was determined by membrane binding of [3H]-nitrobenzylthioinosine, an antagonist of nucleoside transport. Both muskrat and GP hearts responded to 30 min of hypoxic perfusion by releasing ADO into the coronary effluent; however, the muskrat hearts released approximately five times more than the GP hearts. When hearts were subjected to hypoxia in the presence of ADO deaminase, theophylline, or 8-(p-sulfophenyl)theophylline, the hypoxia-induced bradycardia was blocked in the GP hearts and either slightly reduced or not affected in muskrat hearts. In contrast to GP hearts, muskrat hearts release larger amounts of ADO during hypoxia and are more sensitive to the negative chronotropic effects of exogenously administered ADO; yet the hypoxia-induced bradycardia does not appear to be exclusively mediated by ADO in the muskrat as it is in the isolated GP heart.

Adenosine↗
PubMed1993

Platelet membrane-actin interaction.

In order to investigate how human platelet membranes associate with cytoskeletal proteins, purified membranes were extracted with 0.6 M KI (potassium iodide) followed by extraction with 1% octyl glucoside. The depleted membranes contain a significant amount of actin (5% of the actin that was originally present in the purified membranes) which is resistant to extraction by 0.6 M KI. We have examined how this actin interacts with the membrane skeletal fraction and find that the actin is not associated with the membrane directly or indirectly through any of the major transmembrane glycoproteins (GpIb, GpIIb, and GpIIIa), or any known specific linker proteins such as actin binding protein (ABP), alpha-actinin, or spectrin. The results of an analysis of the membrane skeletal preparation using nonreducing sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) does indicate, however, that the actin, along with other proteins, exists in the form of two high molecular weight complexes. We have examined the effect of potassium iodide-octyl glucoside (KI-OG) extracted membranes upon (1) the polymerization of rabbit muscle G-actin, and (2) the actin activated Mg(2+)-dependent ATPase activity of rat skeletal muscle myosin. Based on the results of these experiments we have concluded that the actin is available for interaction with exogenously added proteins and that it might possibly be in a filamentous form. These results are compelling considering the role that the cytoskeleton is thought to play in the physiological functioning of the platelet.

Actins↗
PubMed1992

Anti-hepatitis C virus screening will reduce the incidence of post-transfusion hepatitis C also in low-risk areas.

The incidence of post-transfusion hepatitis non-A, non-B (PTH-NANB) was prospectively assessed in two areas in the southeast region of Sweden. Patients undergoing hip arthroplasty were studied with blood sampling for alanine aminotransferase analysis before and at 2, 3, and 4 months after transfusion. Of the patients 97% and 82% were transfused and received a mean of 5.5 and 3.4 units in Linköping and Oskarshamn, respectively. None of 38 patients in Oskarshamn but 4 of 144 patients (2.8%) in Linköping contracted PTH-NANB. Two of these four patients developed antibodies against hepatitis C virus (HCV) by the first-generation anti-HCV enzyme-linked immunosorbent assay (ELISA) (C100). The other two patients remained negative by this test. HCV infection was, however, indicated in all four patients by positive second-generation anti-HCV ELISA confirmed by positive second-generation recombinant immunoblot assay (4-RIBA). Three of the patients were positive by polymerase chain reaction (PCR). Serum from one blood donor to the four hepatitis patients (altogether three donors) was found positive by first- and second-generation anti-HCV ELISA and 4-RIBA and was also PCR-positive. Three other blood donors, who did not transmit hepatitis, were anti-HCV ELISA (C100)-positive. This study shows that if anti-HCV ELISA had been available at the start of the trial, all cases of PTH would have been avoided at the expense of only 0.7% transfusion units discarded. Routine anti-HCV ELISA testing of all transfusion units will reduce the incidence of PTH-C even in low-risk areas.

Adult↗