An investigation of sodium transport in barnacle muscle fibres by means of the microsyringe technique

1. The cation composition of single barnacle muscle fibres following damage by axial insertion of a microsyringe has been measured. The Na and Ca contents of these fibres were raised.2. Electronmicroscopic studies of fibres following insertion of a microsyringe indicated that the damage done resulted in tubular obstruction of the T-system.3. Fibres loaded with radiosodium by micro-injection showed that the Na(*) efflux declined exponentially with time, but that in most fibres the slope ratio of d/dt ln [Na(*)](1) to d/dt (ln d[Na(*)](i)/dt) was less than unity. Injections of distilled water deep in the fibre failed to influence the course of the Na(*) efflux.4. K removal reduced the Na efflux by 47%. However, a few fibres displayed very little K-dependence.5. When measured in fibres already soaked in a K-free medium for long periods the sodium efflux consisted of a brief rapid phase, followed by a slow phase of Na loss.6. In the presence of 30 mM-K, there was little or no rise in the Na efflux. Raising the external K to 50 or 100 mM caused a marked rise in the Na efflux. Raising the external K to 30 mM in the absence of external Ca(2+) led to a rise in the Na efflux. A high K solution always caused shortening of these fibres.7. Internal application of 1 M or 1 mM-CaCl(2) often caused a significant rise in the Na efflux.8. Internal application of 2.5 or 5 M saline caused a prompt and large fall in the Na efflux. In the presence of high K saline-loaded fibres failed to contract.9. Internal application of 0.5 M-ATP stimulated the Na efflux. A larger effect was not observed in fibres pre-treated with 2 M-MgCl(2). Internal application of 0.5 M-ArP was without effect.10. The results indicate that the barnacle fibre is a suitable preparation for the study of Na fluxes by means of the micro-injection technique. They also indicate that the mechanism regulating the Na efflux is not quite the same as that found in squid axon or frog muscle.

Early effects of illumination on the activity of some photosynthetic enzymes

Leaves of dark-grown corn (Zea mays) were illuminated for periods ranging from 3 minutes to 12 hours. The changes in the activities of ribose-5-phosphate isomerase, ribulose-5-phosphate kinase, and ribulose-1,5-diphosphate carboxylase were followed.The activity of ribose-5-phosphate isomerase did not change significantly until between 12 and 24 hours of illumination. An increase in ribulose-5-phosphate kinase activity occurred after a lag of about 6 hours. The increase in carboxylase activity began after 3 minutes of illumination and increased until after 3 to 6 hours in the light, after which it began to decline. The increases in these enzymes appear to be the result of protein synthesis.