A survey is made for recent development in X-ray diffraction studies on the excitable tissues, with special emphasis upon biological and lipid membranes.
The exposure or counting time needed to observe diffraction patterns from muscles and membranes has been very much shortened recently by the combined use of the total reflection mirror, the curved monochrometer and the position sensitive proportional counter.
There are two approaches in determining ρ (z) of membranes from diffraction data, where z is the coordinate normal to the membrane and ρ (z) is the projection of the electron density distribution to the z axis. One of them is to use Bragg reflections from the lamellar phase of membrane-water system and the other is to use continuous diffraction patterns from membranes dispersed in water, where relative positions of membranes have no correlation. These two approaches are discussed referring to results on lecithin (dipalmitoyl phosphatidylcholine) membranes obtained recently by Y. Inoko and by T. Yamaguchi and K. Furuya. The former has investigated the lamellar phase of the lecithin-water system and the latter have obtained continuous diffraction patterns in good contrast from UO2++ -decorated lecithin double layers dispersed in water. Calculated ρ (z) in these two cases are presented.
