One of the most active and productive areas of biological science in the
past decade has been the study of the biochemical and biophysical prop-
erties of cell membranes. There is little doubt that membranes are
essen- tial components of all cellular systems and that each type of
membrane manifests specific and characteristic cellular functions. In
the nervous system, important events such as neurotransmission, receptor
binding, ion transport, axonal transport, and cell uptake are all known
to take place within the neural cell membrane. Phospholipids, one of the
major components of membranes, not only provide the membrane with its
structural integrity and physical proper- ties, but also play an
important role in regulating membrane function. Attention has recently
been focused on the asymmetric localization of these molecules, the
identification of discrete metabolic pools of phospholipids within the
membrane matrix, and their involvement in sig- nal transmission.
Although synaptic membranes generally lack an active mechanism for the
de novo biosynthesis of phospholipids, a number of enzymic routes are
present for their interconversions and for facilitating metabolic
turnover. Metabolites generated during the interconversion reactions may
also exert a great influence in modulating membrane func- tions. The
phosphogylcerides of neural membranes are especially enriched in
polyunsaturated fatty acids. However, only very small amounts of these
fatty acids are present in the free form, and they are maintained in
dynamic equilibrium with the membrane phospholipids.
