Demonstration of a specific C3a receptor on guinea pig platelets

Journal Article · Sun May 15 04:00:00 EDT 1988 · J. Immunol.; (United States)

OSTI ID:7196287

Fukuoka, Y; Hugli, T E

Guinea pig platelets reportedly contain receptors specific for the anaphylatoxin C3a based on both ligand-binding studies and functional responses. A portion of the human 125I-C3a that binds to guinea pig platelets is competitively displaced by excess unlabeled C3a; however, the majority of ligand uptake was nonspecific. Uptake of 125I-C3a by guinea pig platelets is maximal in 1 min, and stimulation of guinea pig platelets by thrombin, ADP, or the Ca2+ ionophore A23187 showed little influence on binding of the ligand. Scatchard analysis indicated that approximately 1200 binding sites for C3a exist per cell with an estimated Kd of 8 x 10(-10) M. Human C3a des Arg also binds to guinea pig platelets, but Scatchard analysis indicated that no specific binding occurred. Because the ligand-binding studies were complicated by high levels of nonspecific uptake, we attempted to chemically cross-link the C3a molecule to a specific component on the platelet surface. Cross-linkage of 125I-C3a to guinea pig platelets with bis(sulfosuccinimidyl)suberate revealed radioactive complexes at 105,000 and 115,000 m.w. on SDS-PAGE gels by autoradiographic analysis. In the presence of excess unlabeled C3a, complex formation was inhibited. No cross-linkage could be demonstrated between the inactive 125I-C3a des Arg and the putative C3a-R on guinea pig platelets. Human C3a, but not C3a des Arg induces serotonin release and aggregation of the guinea pig platelets. Human C3a was unable to induce either serotonin release or promote aggregation of human platelets. Uptake of human 125I-C3a by human platelets was not saturable, and Scatchard analysis was inconclusive. Attempts to cross-link 125I-C3a to components on the surface of human platelets also failed to reveal a ligand-receptor complex. Therefore, we conclude that guinea pig platelets have specific surface receptors to C3a and that human platelets appear devoid of receptors to the anaphylatoxin.

• Research Organization: Tohoku Univ., Sendai (Japan)
• OSTI ID: 7196287
• Journal Information: J. Immunol.; (United States), Journal Name: J. Immunol.; (United States) Vol. 140:10; ISSN JOIMA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMINES
ANIMALS
AROMATICS
AUTONOMIC NERVOUS SYSTEM AGENTS
AUTORADIOGRAPHY
AZAARENES
AZOLES
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BLOOD PLATELETS
BODY FLUIDS
CHEMICAL REACTIONS
COMPLEMENT
CROSS-LINKING
DAYS LIVING RADIOISOTOPES
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
ELECTROPHORESIS
GUINEA PIGS
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
INDOLES
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPES
KINETICS
LIGANDS
MAMMALS
MAN
MATERIALS
MEMBRANE PROTEINS
NEUROREGULATORS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PEPTIDES
POLYMERIZATION
PRIMATES
PROTEINS
PYRROLES
RADIOISOTOPES
RADIOPROTECTIVE SUBSTANCES
REACTION KINETICS
RECEPTORS
RODENTS
SECRETION
SEROTONIN
SPECIFICITY
SYMPATHOMIMETICS
TRYPTAMINES
VERTEBRATES