Observations upon the metabolism of fluorocitrate in rats

Part 1. Reduced toxicity of fluorocitrate by the oral route in rats In contrast to the extreme toxicity of fluorocitrate inside mitochondria or the brain, growing rats were able to drink sublethal doses of the carbon fluorine compound for periods up to 7 months without harm ; the total dose so consumed was 6 times a lethal dose given by intraperitoneal injection. Part 2. The metabolism of fluorocitrate in the rat In an attempt to explain the reduced ' oral ’ toxicity using fluorocitrate labelled with 14 C in the 2 position, it was found that the mixed oxidase system in rat liver microsomes did not metabolize the 14 C moiety. When given by the intraperitoneal route, the labelled carbon was mainly excreted in the urine within 48 h. On the other hand, when non-labelled Na fluorocitrate (synthetic) was given to rats in a single oral dose, much inorganic fluoride was excreted together with citrate. Hence rat tissues can remove inorganic fluoride from fluorocitrate. This proof required a preliminary stabilization of the urinary excretion of inorganic fluoride on a special diet, as the ordinary rat pellets (41 B) may contain up to 20 parts/10 6 of inorganic fluoride.

The problem of cytoplasmic integration

Though little considered, the problem of integration in the living cell is fundamental. Older ideas of foam structure (Bütschli) were cogently criticized when Hardy (1899) found that fixatives produced in gelatin structures that were similar to those induced by the same fixatives in cells. The sceptical attitude to histology (light microscope) extended until the development of phase-contrast microscopy (Zernicke 1935; Hughes & Swann 1948). Further observations by Hardy (1913) led him to propose orientation of molecules in surfaces and interfaces, work extensively developed by others. At a time when little structure could be seen in cells (1929), I proposed on logical grounds that there was present a coordinating fluid cytoskeleton based for its chemistry upon interfacial molecular structure. This view of a microheterogeneous organization led to the idea that enzymes were under the control of the cytoskeleton, an idea most unpopular with those contented with the ‘bag of specific enzymes’ hypothesis. With the development of the electron microscope, all doubt as to organelle structures has vanished. A ciné film will be shown (Buffa, Modena with Godina and Barasa, Turin), illustrating well the living complications; also, in comparison, a modern e. m. picture of a gelatin gel (R. Reed). Though doubts as to the existence of internal structures have gone, there still remains the puzzle as to how the cell is integrated on a molecular basis, and adjusted to environmental stimuli and otherwise. Every change in the individual reactions of a cell is based upon some phase of chemistry or physical chemistry. Can we still believe, however, that the whole living cell is merely an extremely complex chemical equilibrium, or have we still to look for some tenuous coordinating structure, fulfilling the role the nervous system does in the animal? This might indeed be a channel for the transmission of electrons. Whether such an integrating cytoskeleton is present is not an academic question, because it would be an important factor in the development of malignant change.

Studies on the toxicity of copper. II. The behaviour of microsomal membrane ATPase of the pigeon's brain tissue to copper and some other metallic substances

Earlier work on the toxicity of copper (Cu 2+ ) in vivo suggested that the metal exerted its effect on the cell membrane, probably the microsomal ATP ase. The microsomal ATP ase prepared from pigeon brain is activated by Mg but little by Na and K. 20 µ m Cu achieved maximum inhibition reducing enzyme activity by approximately 25%. The same preparation was only slightly sensitive to ouabain, the effects of copper and ouabain were not additive. The toxicity of cadmium approached that of copper. Cobalt and thorium were not toxic in the concentration range studied. The microsomal ATP ase appears to have a thiol group at the active catalytic centre. It is potentiated by the thiols, BAL , penicillamine, dithiocarbamate and thioctic acid. Only with thioctic acid was there any reversal of Cu 2+ toxicity. We conclude that there are at least three components in the pigeon’s brain microsomal ATP ase : (1) resistant to copper and to ouabain, (2) inhibited by copper, only slightly inhibited by ouabain (3) stimulated by -SH compounds, sensitive to ouabain and copper. We also conclude that inhibition of membrane ATP ase may be responsible for the excitatory effect of Cu 2+ in vivo .

Studies on the toxicity of copper. I. The toxic action of copper in vivo and in vitro

With the object of throwing light upon the brain damage found in patients with Wilson’s disease (hepato-lenticular degeneration) due to the accumulation of copper, the effect of Cu 2+ has been investigated in pigeons. Subarachnoid injections of Cu 2+ (10 to 25 µ g) led to rapid onset of convulsions and death. These concentrations of Cu 2+ inhibited pigeon and rat b rain mitochondria; more organized tissue breis or slices showed no significant inhibition of oxygen up take at Cu +2 concentration inducing convulsions in vivo . Studies with radioactive copper ( 64 Cu) showed that the injected copper was widely distributed in the brain, though maximal near the site of injection. Centrifugation showed a high specific activity in the ATP -ase-rich microsomal fraction. Thorium in concentrations similar to Cu 2+ was not toxic. From this we suggest that the Cu 2+ does not alter the charge on some membrane surface. Since the effect of the copper is immediate, and since it does not affect respiration of slices in these low concentrations, we conclude that it is exerting its convulsive effect directly upon the cell surfaces.