The efflux of 45Ca 2+ and [ 3H]γ-aminobutyric acid from cat cerebral cortex

Abstract

The efflux of both 45Ca 2+ and [ 3H]GABA from suprasylvian cortex of cat has been studied in vivo. After pre-incubating the cortex with radioactivity for 90 min, superfusion with non-radioactive medium was carried out using 0.8 ml vol. changed at 10 min intervals. Increases in the calcium concentration of the medium resulted in greater efflux of both 45Ca 2+ and [ 3H]GABA, and the effect on [ 3H]GABA efflux was potentiated by AOAA. The effect of a 1mM increment in Ca 2+ concentration was only slightly less than that of a 20mM increment. Adding Mg 2+ to the medium did not produce increases comparable to added Ca 2+, whereas electrical stimulation of the cortex had no effect on the efflux of either 45Ca 2+ or [ 3H]GABA. Thiosemicarbazide, an epileptogenic agent, resulted in a slightly irregular efflux of 45Ca 2+ with peaks visible at times of seizure activity. The efflux of 3H 2O and 14C-(car☐yl)-inulin could not be correlated with any of the above treatments. The efflux of [ 3H]GABA from the cortex is considered to originate from synaptic terminals and that of 45Ca 2+ may be the result of reactions at the membrane triggering the release or turnover of calcium.