Two optical measurement techniques will be used to study changes in molecular conformation associated with excitability of nerve cell membranes. Two nerve preparations will used; isolated olfactory nerves of garfish and internally perfused and voltage- clamped segments of squid giant axons. Previous work by the author has linked changes in optical retardation (birefringence) with molecular motion underlying activation and inactivation of sodium channels of squid axons. This method is sensitive to the orientation of molecular dipoles, here the re-orientation of peptide bonds within the sodium channel molecule is thought to produce the signals. In many ways this signal is comparable to polarization (gating) currents studied by others. Various treatments which modify nerve excitability will be investigated using the birefringence methods. In particular, the effects of calcium concentration on the birefringence response to voltage changes will be measured and correlated with the effects on the electrical current . The second optical measurement is of optical rotation (circular birefringence). Recently a Japanese worker has reported a change in optical rotation associated with action potentials in lobster nerves and in squid axons. This rotation signal had a different time course than the birefringence signal .Optical rotation senses the chirality of molecules. The most likely candidate for the signals observed are changes in the secondary, structure of a protein, for example, a change from alpha-helix to beta-sheet is a change in the overall chirality of the peptide bonds. In this project an attempt will be made to repeat the original observations in gas nerves and squid axons using the original method of modulating the polarization of the incident light beam and a new method based on a two-frequency (Zeeman split) laser. The project will then continue to characterize the rotation signal with internally perfused voltage-clamped squid axons and use the variety of manipulations developed to test the association of the birefringence response to see if the rotation response reflects changes in the sodium channel molecules and its relation to the birefringence, gating and ionic sodium current responses. Healthy nerves are excitable in a balanced way and alterations of excitability are seen in disease states and also during treatments such as anesthesia. This project will provide information at the molecular and sub-molecular level to allow us to understand excitability and its variation. There is a long history of the application of the results obtained on invertebrate nerve cells to vertebrates including humans. In addition studies of nerve sodium channels have often led to understanding of other channels in other tissues with potential health relatedness.
| Landowne, D (1993) Measuring nerve excitation with polarized light. Jpn J Physiol 43 Suppl 1:S7-11 |
