Differential effects of veratridine and calcium on the release of [(3)H]noradrenaline and [(14)C]?-aminoisobutyrate from rat brain cortex slices.
The efflux of [(3)H]noradrenaline (NA) and of the non transmitter, non metabolizable, amino acid [(14)C]?-aminoisobutyrate (AIB), was followed simultaneously from superfused rat brain cortex thin slices, that had been preloaded with those substances. Short (2 min) "pulses" of increasing veratridine concentrations were applied at 10 min intervals. When calcium in the superfusion fluid was 1 mM, [(3)H]NA efflux increased progressively with pulses of 1, 3, 10 and 30 ?M veratridine, but further increase to 100 ?M resulted in a decrease of the induced (3)H-efflux. Veratridine-enhanced [(3)H]NA efflux decreased considerably in 0.1 mM calcium and was virtually suppressed when no calcium was added to the superfusion fluid. In 1 mM calcium, the efflux of [(14)C] AIB was increased progressively by pulses of 10, 30 and 100 ?M veratridine, but no increase in efflux was seen with 1 or 3 ?M drug. In 0.1 mM, or without added calcium, the induced efflux of [(14)C]AIB was markedly increased. Similar findings were seen when a long (10 min) pulse of 10 ?M veratridine was given. After such long pulses there was a rapid return of AIB efflux to pre-veratridine levels if calcium was 1 mM, but in the absence of added calcium, the return to baseline levels of both [(3)H]NA and, especially, that of [(14)C]AIB efflux, was greatly impaired. The veratridine enhanced efflux of both NA and AIB was entirely blocked by 1 ?M tetrodotoxin.
Pizarro
M
M
Department of Physiology and Biophysics, Faculty of Medicine, Universidad de Chile, Casilla 137-D, Santiago, Chile.
Valdivieso
M P
MP
Orrego
F
F