MEMBRANE BASIS OF VISUAL EXCITATION

The proposed research is directed towards elucidation of the role of
membranes in the visual process. In the broadest of terms, our goal is to
determine the molecular events responsible for membrane excitability in the
vertebrate rod. At this membrane level, several puzzling and outstanding
questions are evident, which may be relevant to a better understanding of
vision and its disorders. The most immediate objectives of the project can
be grouped into three general areas: (i) investigation of the structural
and dynamic properties of the highly polyunsaturated phsopholipids which
comprise the fundamental bilayer matrix of the retinal disk membranes, (ii)
studies of the conformation of rhodopsin and the nature of its interaction
with the native retinal disk membrane phospholipids, as well as synthetic
phospholipids used for membrane reconstitution and detergents used for
membrane solubilization, (iii) studies of the role of electrical and
osmotic forces in determining the properties of the lipid and protein
components of the rod outer segment disk membranes. The above problems
will be approached primarily through the use of various biophysical
techniques. A major emphasis will be to further develop and employ nuclear
magnetic resonance (NMR) methods for the study of both the protein and
lipid components of the photoreceptor membrane. Such NMR methods are
highly novel and are capable of providing detailed information regarding
the ordering and motional properties of membrane constituents, without the
introduction of probe molecules, which may perturb the bilayer structure.
Thus, we intend to investigate problems such as the role of membrane
thickness, degree of polyunsaturation, osmotic forces, transmembrane
electrical potential in determining the conformation and proper
photochemical functionality of rhodopsin. Using these methods, we hope to
provide during the next five years a fairly complete picture of the mutual
interaction of lipid and protein and their relation to function in the
vertebrate rod outer segment, a particularly promising model fo excitable
membranes in general.