BIOCHEMICAL CHARACTERIZATION OF THE NEURON: RIBONUCLEIC ACID COMPOSITION OF THE NEURONAL CELL BODIES

Abstract— The fluorescence of chlorotetracycline (CTC) in the presence of synaptosomes isolated from sheep brain is selectively increased by Ca²⁺ under conditions in which Mg²⁺, Na⁺, K⁺, Li⁺ or choline have only a small effect. The monovalent cations release bound Ca²⁺ from synaptosomes, and this effect is reflected by a decrease in the CTC fluorescence. Under optimal conditions there is a near parallelism between Ca²⁺ and CTC binding to the synaptosomes membranes, and Li⁺ is the monovalent cation tested which interferes the most with the binding of both substances. These results obtained in a predominantly sucrose medium become less distinct when media simulating physiological composition are utilized, which limits the usefulness of the method. Brain mitochondria and myelin also bind Ca²⁺ and CTC. The ratio of the fluorescence signal (or CTC bound) to Ca²⁺ bound is highest of all for mitochondrial membranes, and the apparent fluorescence quantum yield of CTC is also the highest in these membranes, which suggests that the Ca²⁺ in these membranes is localized in a more apolar region than is the case for synaptosomes and myelin.