The effect of electrical stimulation on the incorporation of L-[U-14C] valine into the protein of chopped tissue from guinea-pig cerebral cortex

Effects of handling and etherization on incorporation of [3H] lysine into protein of mouse brain and liver

A standardized handling experience of 20 sec duration elevated the amount of radioactive lysine incorporated into brain total proteins during a 10 min labeling period begun either 10 min or 30 min after the handling. Etherization for 20 sec produced similar metabolic changes. Incorporation of [3H] lysine into liver proteins was minimally affected by handling, while slightly altered by etherization. The metabolic changes detected in the brain after handling did not appear to be side-effects of changes in blood-borne radioactivity. The results indicate that laboratory stresses often thought to be of minor importance can have large effects on ordinary assays of protein metabolism in brain.

Distribution of protein-bound radioactivity in brain slices of the adult rat incubated with labelled leucine

The distribution of protein-bound labelled leucine in brain cortex slices, prepared from adult rats by various methods and incubated with [14C]- or [3H]leucine, was investigated by autoradiography. In the first and second slices a marked gradient of incorporated radioactivity from the cut surface to the slice interior was observed. Very high labelling of leptomeningeal cells and vessels enhanced further the inhomogeneity of radioactivity distribution. Light microscopic examination of incubated slices revealed morphological alterations of neurones, especially in the vicinity of the cut surface. The comparison of grain density over neurones and their satellite glia indicated markedly higher incorporation into the latter. The ATP level in slices at the end of incubation reflected the method of slice preparation and morphological integrity. Inhomogeneity of incorporated radioactivity distribution in brain slices contrasted with the uniform labelling of cortical cells in vivo, and may represent at least one reason for the low estimates of protein synthesis rate in brain cortex slices.

The influence of the intracellular concentration of sodium on the uptake of L-( 14 C)valine by chopped tissue from cerebral cortex

1. The intracellular concentrations of sodium, potassium, ATP and creatine phosphate in chopped tissue from guinea-pig cerebral cortex were altered by a 10min period of electrical stimulation. 2. The ability of the tissue to take up l-[(14)C]valine and incorporate it into protein was tested at various times after the cessation of electrical stimulation. 3. The restoration of the ability of the tissue to accumulate l-[(14)C]valine correlated closely with the restoration of the resting intracellular concentrations of sodium and ATP.

The effect of electrical stimulation and ouabain on the uptake and efflux of L-[U-14C] valine in chopped tissue from guinea-pig cerebral cortex

1. Chopped tissue from guinea-pig cerebral cortex carried out an energy-dependent accumulation of l-[(14)C]valine. 2. The uptake was dependent on the extracellular concentration of Na(+) and was markedly inhibited by ouabain (20mum). The extent of the inhibition of uptake by ouabain was also Na(+)-dependent. 3. The accumulation of labelled valine was not directly dependent on the ATP and creatine phosphate contents of the slices. 4. Electrical stimulation increased the rate of [(14)C]valine uptake at first but ultimately led to a net loss of the label so that the amount of label present in the tissue was lower than in the controls. 5. The rate of loss of label during prolonged stimulation was dependent on the extracellular concentration of Na(+). 6. The efflux of labelled valine from slices preloaded at 164mm-Na(+) was studied at 164, 80 and 40mm-Na(+) with and without electrical stimulation or ouabain. 7. Lowering the Na(+) concentration or adding ouabain increased the rate of efflux. 8. Electrical stimulation had little effect on the rate of efflux at first but ultimately led to a more complete loss of label from the tissue than occurred in the control. A kinetic analysis of the efflux curves was attempted.

The effect of preganglionic stimulation on the incorporation of L-[U-14C] valine into the protein of the superior cervical ganglion of the guinea pig

1. Superior cervical ganglia from the guinea pig carry out an energy-dependent incorporation of l-[(14)C]valine into protein in vitro. 2. Stimulation of the preganglionic nerve at a physiological frequency for more than a few minutes decreases the ability of the ganglia to incorporate labelled valine into protein.