title: Role of Ca++ in virus-induced membrane fusion. Ca++ accumulation and ultrastructural changes induced by Sendai virus in chicken erythrocytes.
abstract: Some of the ultrastructural (freeze-etching technique), morphological, and biochemical effects of Sendai virus interaction with chicken erythrocytes have been studied under fusogenic (in the presence of CaCl2) and nonfusogenic (in the presence of ethyleneglycol-bis-N,N'-tetraacetic acid, [EGTA]) conditions. The following phenomena occur, irrespective of the presence of CaCl2 or EGTA: (a) binding of iodinated virus particles to chicken erythrocytes at 4 degrees C and their partial release from the cells at 37 degrees C; (b) gradual incorporation of the viral envelope and viral M-protein into plasma membrane, as visualized in the protoplasmic and exoplasmic fracture (P and E, respectively) faces of the membrane; and (c) virus-dependent transient clustering of intramembrane particles at 4 degrees C, which is reversible after transferring the cells back to 37 degrees C. The following virus-induced phenomena occur only in the presence of CaCl2: (a) rounding of cells followed by their fusion; (b) transient decrease in the density of intramembrane particles; and (c) the virus induces uptake of 45CaCl2 by chicken erythrocytes. The uptake is specific as it is inhibited by LaCl3, and no accumulation of [14C]glucose-1-phosphate ([14C]G-1-P) could be observed under the 45 CaCl2 uptake conditions. The data show that fusion of virus with plasma membrane is a Ca++-independent process and, as such, it should be distinguished from the virus-induced membrane-membrane and cell fusion processes. The latter is absolutely dependent on the rise of intracellular Ca++, as reflected by the fact that Ca++-induced rounding of chicken erythrocytes always precedes fusion (Volsky, D. and A. Loyter. 1977.Biochim. Biophys. Acta 471:253--259).
mesh_terms: D000327:Adsorption; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology*; D002478:Cells, Cultured; D002645:Chickens; D004533:Egtazic Acid / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000187:drug effects* / Q000648:ultrastructure; D004912:Erythrocytes / Q000187:drug effects* / Q000378:metabolism / Q000382:microbiology*; D005613:Freeze Etching; D010222:Parainfluenza Virus 1, Human / Q000187:drug effects* / Q000648:ultrastructure
chemical_list: D004533:Egtazic Acid; D002122:Calcium Chloride; D002118:Calcium