Fusion of Isolated Sarcoplasmic Reticulum Membranes

Abstract

Abstract Fragmented sarcoplasmic reticulum (FSR) vesicles from rabbit muscle were suspended in 1.5 - 5% glycerol solutions and were pelleted onto aluminum foil disks in a modified centrifuge tube. Examination of these pellets in the electron microscope after drying for 2 - 2.5, 4 - 5.5, and 21 hours revealed a progression of changes. First, distances between individual, round vesicles decreases. Next, somewhat flattened vesicles establish limited areas of contact with adjacent vesicles. Finally, vesicle fusion occurs and extended areas of double bilayers are formed. A water loss-time interaction appears to be needed for the fusion process. A Hg-phenyl azoferritin com­ pound was used as a marker to identify intra- and extra-vesicular space in the fused samples. Quantitative measurements of birefringence during imbibition of pellet slices in a graded series of glycerol solutions indicates a steadily increasing amount of birefringence until 60 - 80% glycerol (η = 1.41 -1.43) is readied. The plateau seen in this part of the curve is again followed by steadily increasing birefringence at higher glycerol concentrations. This interruption in the birefringence curve is presumably due to a matching of the refractive indices of the glycerol solution and a lipid component in the membranes.