title: Physical properties of muscle cell membranes during fusion. A fluorescence polarization study with the ionophore A23187.
abstract: 1. The fluorescence polarization of A23187 is used to detect physical changes in myoblast membranes produced by Ca2+ concentrations which are able to trigger fusion. Temperature scans reveal a Ca2+-dependent fluidity increase in the microenvironment of the ionophore above 37 degree C. 2. Time-dependent polarization measurements show two different effects. The first one consists of a fast polarization increase which reaches its maximum after 5-10 min. This change could be explained by a Ca2+-induced phase separation of acidic and neutral phospholipids in the membrane. The second effect is a slow polarization decrease over 2-3 h subsequent to the fast increase. 3. The information derived from the fluorescence polarization is in accordance with the characteristics of the fusion of myoblast cells regarding the dependence on Ca2+ concentration, the inhibition by Mg2+ and lysolecithin as well as a typical temperature of 35-37 degree C where fusion rate changes abruptly.
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium; D002459:Cell Fusion; D002462:Cell Membrane / Q000187:drug effects; D002642:Chick Embryo; D004912:Erythrocytes; D008244:Lysophosphatidylcholines; D008274:Magnesium; D009132:Muscles / Q000648:ultrastructure*; D010169:Palmitic Acids; D010713:Phosphatidylcholines; D011048:Polarography; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D000900:Anti-Bacterial Agents; D008244:Lysophosphatidylcholines; D010169:Palmitic Acids; D010713:Phosphatidylcholines; D000001:Calcimycin; D008274:Magnesium; D002118:Calcium