Freeze-fracture cytochemistry of sympathetic ganglia. Distribution of filipin and tomatin induced membrane deformations in neurons and satellite cells

Increase in reactive cholesterol in the presynaptic membrane of depolarized Torpedo synaptosomes: blockade by botulinum toxin type A

We have investigated the redistribution of filipin-cholesterol complexes at freeze-fractured presynaptic membrane of pure cholinergic synaptosomes isolated from Torpedo electric organ during acetylcholine release. After chemical depolarization, filipin-induced lesions increase at the presynaptic membrane. These changes do not take place when synaptosomes are stimulated in a calcium-free medium. Botulinum neurotoxin type A blocks both acetylcholine release and the rearrangement of filipin-induced lesions induced by depolarization. Since botulinum neurotoxin type A does not block either membrane depolarization or calcium entry into the nerve terminal, our results suggest that the redistribution of filipin-cholesterol complexes is linked to the acetylcholine release process.

Filipin-labelled complexes are polarized in their distribution in the cytoplasm of meiotically mature mouse eggs

Unfertilized (germinal vesicle [GV] stage, superovulated and naturally ovulated) and fertilized mouse eggs were treated with the polyene antibiotic filipin, which complexes with unesterified sterols; specimens were observed by fluorescence microscopy and scanning electron microscopy (SEM). In all oocytes examined, filipin fluorescence was localized to the plasma membrane and to subcellular structures of various sizes. In the unfertilized oocyte, polarity was observed both in the plasma membrane stain and in the pattern formed by the subcellular structures. SEM of filipin-treated oocytes had several characteristic features including a specific distribution of heterogeneous microvilli that appears to have a spatial relationship with the fluorescent pattern of the filipin-positive subcellular structures. In GV stage and fertilized eggs the filipin-positive subcellular structures were associated with the germinal vesicle and in fertilized eggs they were associated with the site of polar body abstriction.

Labeling of cholesterol with filipin in cellular membranes of parenchymatous organs. Standardization of incubation conditions

Filipin is used for ultrastructural cytochemical localization of cholesterol in biological membranes. It binds to unesterified 3 beta-hydroxy-sterols forming 25 nm complexes which are readily recognized in freeze-fracture replicas. Since most investigations with filipin have been performed in isolated cells (tissue culture, cell suspensions etc.) we have investigated the conditions for reproducible labeling of cholesterol in membranes of parenchymatous organs. Vibratome sections of rat kidney fixed by glutaraldehyde perfusion were incubated in filipin and freeze-fracture replicas were prepared using standard techniques. The concentration of filipin, the thickness of vibratome sections and the incubation time and temperature were varied over a wide range. Optimal results were obtained with 50 micron thick tissue slices incubated in 400 micrograms/ml of filipin for 46 h at room temperature. Under these conditions lysosomes were consistently labeled while mitochondria and the endoplasmatic reticulum were negative. Peroxisomes showed a little or no labeling at all while the nuclear envelope was heavily labeled in some cells being negative in others. The method described here should be useful in investigation of the role of cholesterol in function of biological membranes in parenchymatous organs and compact tissues.

Freeze-fracture cytochemistry of sympathetic ganglia. Distribution of filipin and tomatin induced membrane deformations in neurons and satellite cells

Application of filipin to sympathetic ganglia results in membrane deformations in both the neurons and the satellite cells. The plasma membranes of the principal ganglion cells show a non-homogeneous distribution of filipin induced deformations with fewer deformations in the perikaryal plasma membrane than in the nerve fiber membrane. The filipin induced membrane lesions are correlated to the number of IMPs of the neuronal membrane i.e. a high density of intramembrane particles (IMP) gives fewer deformations and vice versa. The membrane of the satellite cells contain a higher density of probe induced lesions than the neuronal membrane. The filipin induced deformations in the satellite cells are not correlated to the number of IMPs or to the number of orthogonal arrays of small particles (OAP). Specialized membrane areas such as the gap junction is always devoided of filipin induced lesions. A similar distribution of membrane lesions was found when tomatin was used instead of filipin. These results indicate a possible difference in lipid content between various parts of the neurons and between the neuronal and satellite cell plasma membrane in guinea pig sympathetic ganglia.