X-ray diffraction study of the live squid retina.
In previous studies of invertebrate rhabdomes by X-ray diffraction, glutaraldehyde fixation of the retina was used because this tissue is very labile and, without fixation, disintegrates within an hour of dissection. However, with conventional X-ray apparatus more than ten hours exposure time was needed to record a diffraction pattern. In this study, X-ray diffraction patterns from unfixed squid retina could be successfully obtained by use of synchrotron radiation and a storage phosphor screen as detector. The diffraction spots were indexed on a two-dimensional hexagonal lattice of 60 nm. X-ray data was analysed by comparing Patterson functions calculated from the diffraction intensities with those based on model building. The hexagonal shape of microvillar cross section was suggested by the systematic weakness of (0, k) reflections beyond k = 4 and the appearance of the six symmetry-related diffuse maxima around (4 nm)-1. The best-fitting model showed a large gap between adjacent microvilli (approximately 12 nm), which has been expected (for ionic current flow through the inter-microvillus space to generate the membrane potential) but not observed with the chemically fixed retina, possibly due to an artifact of fixation. Also, the existence of massive inter-microvillus material, scarcely observed by conventional electron microscopy, has been confirmed.
Hamanaka
T
T
Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Japan.
Kito
Y
Y
Seidou
M
M
Wakabayashi
K
K
Michinomae
M
M
Amemiya
Y
Y
D000818:Animals; D049832:Decapodiformes / Q000648:ultrastructure*; D008871:Microvilli / Q000648:ultrastructure; D008953:Models, Anatomic; D017956:Photoreceptor Cells, Invertebrate / Q000648:ultrastructure; D012160:Retina / Q000648:ultrastructure*; D014961:X-Ray Diffraction