ABSTRACT
We have demonstrated specific adenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) receptors at heart cell surfaces. Optimal Ap4A binding requires receptor activation. Other Investigators have demonstrated that Ap5A and Ap6A act as vasopressors. We now compare the binding of Ap4A, Ap5A and Ap6A on heart membranes to determine if all three ligands bind to the same receptor and their relative avidities. Anti-Ap4A receptor antibodies inhibit the binding of all three ligands. SDS-PAGE analysis of Ap4A, Ap5A and Ap6A cross-linked to membranes reveals that all three are attached to a 30 kDa peptide. The specific activity for binding to unactivated membranes is similar for all three ligands. However, after receptor activation there is a 3.4x increase in Ap4A binding and a 32.5x decrease in the KD; values remain unchanged for Ap5A and Ap6A. These data indicate that Ap4A, Ap5A and Ap6A bind to the same receptor on cardiac membranes but receptor activation enhances only Ap4A binding.
Subject(s)
Dinucleoside Phosphates/metabolism , Myocardium/metabolism , Receptors, Purinergic P2/metabolism , Animals , Antibodies, Monoclonal , Cell Membrane/metabolism , Dinucleoside Phosphates/chemistry , Female , In Vitro Techniques , Kinetics , Mice , Models, Molecular , Purinergic P2 Receptor Antagonists , ThermodynamicsABSTRACT
The similarities between the tail of asymmetric acetylcholinesterase (AcChE) and collagen prompted us to investigate if asymmetric AcChE, like collagen, can interact with fibronectin. Gradient centrifugation studies revealed that asymmetric, but not globular, AcChE bound to fibronectin and could be cross-linked covalently to fibronectin by plasma transglutaminase. The interaction of asymmetric AcChE with fibronectin paralleled the interaction of fibronectin with collagen. These results raise the possibility that fibronectin may be involved in attaching asymmetric AcChE to cell surfaces.
Subject(s)
Acetylcholinesterase , Fibronectins , Acetylcholinesterase/metabolism , Animals , Collagen , Detergents , Fibronectins/metabolism , Kinetics , Macromolecular Substances , Muscles/enzymology , Octoxynol , Polyethylene Glycols , Protein Binding , Quail , Serum Albumin, Bovine , TrypsinSubject(s)
Cell Adhesion , Molecular Biology , Agglutination , Animals , Blood , Cell Adhesion/drug effects , Cell Aggregation/drug effects , Chick Embryo , Culture Media , Cycloheximide/pharmacology , Depression, Chemical , Edetic Acid/pharmacology , Glucosamine/pharmacology , In Vitro Techniques , Macromolecular Substances , Periodic Acid/pharmacology , Porifera/cytology , Porifera/immunology , Puromycin/pharmacology , Retina/immunology , Stimulation, Chemical , Surface PropertiesABSTRACT
A supernatant medium has been prepared from living embryonic neural retina cells which specifically promotes their histogenetic aggregation. Its function is dependent upon at least two experimentally separable steps: selective uptake and functional utilization.
