Potassium stimulated release of axonally transported radioactivity from slices of rabbit superior colliculus.

The radioactivity in the trichloroacetic acid (TCA) soluble pool in the terminals of the retinal ganglion cells in the superior colliculus (SC) was studied one month after labelling of the nerve cell bodies in the retina with different radioactive amino acids. The TCA soluble fraction in the SC represented a few per cent of the total radioactivity of the isolated tissue and was mainly derived from protein degradation. The perfused slice of the SC responded to high K+ depolarization with an increased release of TCA-soluble radioactivity, while small changes occurred for TCA-precipitable fractions. The evoked release of TCA-soluble radioactivity was particularly prominent after labelling with [3H]glycine. The release was Ca2+-dependent and the response to repetitive depolarization indicated a continuous replenishment of the releasable pool.