ELEVATED EXTRACELLULAR POTASSIUM AS A STIMULUS FOR RELEASING [3H]NOREPINEPHRINE AND [14C]α‐AMINOISOBUTYRATE FROM NEOCORTICAL SLICES. SPECIFICITY AND CALCIUM DEPENDENCY OF THE PROCESS

Abstract —The effect of short (4–6 min)‘pulses’ of elevated extracellular potassium ions K0, in the 10–50 mm range, on the efflux of [3H]norepinephrine [3H]NE) and [14C]α‐aminoisobutyrate (AIB) has been studied in a superfused neocortical thin slice system. At all the concentrations tested high K0 increases the efflux of both NE and AIB, although thc effects on the former are greater. In the absence of calcium ions, or in the presence of 8 mm‐MnCl2, the potassium‐stimulated release of both NE and AIB is severely depressed. However, potassium induced NE release is proportional to extracellular calcium ions in the 0–1.5 mm range, while that of AIB does not continue to increase above 0.2 mm‐calcium. This permissive role of calcium in amino acid efflux is interpreted as due to changes in the inactivation of membrane sodium conductance.