Effects of sodium-deficient media and of a calcium ionophore (A-23187) on the release of (3H)-noradrenaline, (14C)-α-aminoisobutyrate, and (3H)-γ-aminobutyrate from superfused slices of rat neocortex (original) (raw)

The calcium ionophore A-23187, at a concentration of 250 &ml. had no significant effects on the efflux of (3H)-noradrenaline or of ("'C)-a-aminoisobutyrate. in superfused slices from rat neocortex. Sodium-deficient solutions (sodium partiy substituted by choline). however, were found to increase the efflux of ('4~)-~-aminoisobutyrate and of (3H)-~-aminobutyrate. The enhanced efflux of both these substances appeared with no Iatency. was maintained for long periods, and did not change appreciably when calcium was omitted. Media low in sodium enhanced noradrenaline efflux in a more complex manner. There was, initially, a small increase in efflux that was similar both in latency and lack of dependence upon calcium to that of the above amino acids. This was followed by a very large efflux peak of noradrenaline, with a change in the fractional rate constant of up to 0.06 mini. This large efflux peak did not occur when no calcium was added to the superfusing fluid. The efllux of noradrenaline occurred when calcium was replaced by strontium or barium ions, but the latter were less effective. Finally, when media free of added calcium were made sodium-deficient, there was a moderate increase in the efflux of noradrenaline that began after a delay of about 30 min.