Amine weak bases disrupt vesicular storage and promote exocytosis in chromaffin cells

The vesicular contents in bovine chromaffin cells are maintained at high le vels owing to the strong association of its contents, which is promoted by the low vesicular pH. The association is among the catecholamines, Ca2+, AT P, and vesicular proteins. It was found that transient application of a wea k base, methylamine (30 mM), amphetamine (10 mu M), or tyramine (10 mu M), induced exocytotic release. Exposure to these agents was also found to incr ease both cytosolic catecholamine and intracellular Ca2+ concentration, as measured by amperometry and fura-2 fluorescence. Amphetamine, the most pote nt amine with respect to evoking exocytosis, was found to be effective even in buffer without external Ca2+; however, the occurrence of spikes was sup pressed when BAPTA-acetoxymethyl ester was used to complex intracellular Ca 2+. Amphetamine-induced spikes in Ca2+-free medium were not suppressed by t hapsigargin or ruthenium red, inhibitors of the sarco(endo)plasmic reticulu m Ca2+-ATPase and mitochondrial Ca2+ stores. Atomic absorption measurements of amphetamine- and methylamine-treated vesicles reveal that intravesicula r Ca2+ stores are decreased after a 15-min incubation. Taken together, thes e data indicate that amphetamine and methylamine can disrupt vesicular stor es to a sufficient degree that Ca2+ can escape and trigger exocytosis.