PREFERENTIAL LOCALIZATION OF EXOCYTOTIC ACTIVE ZONES IN THE TERMINALSOF NEURITE-EMITTING CHROMAFFIN CELLS

Amperometry using 2.5 mu m radius carbon fiber electrodes was employed to study exocytotic catecholamine release from individual cultured bo vine chromaffin cells. The secretory responses to either direct depola rization or nicotinic receptor stimulation were focal in nature in bot h round and neurite-emitting tells. In contrast to the random distribu tion of active sites found in round cells, bipolar and tripolar chroma ffin cells had responsive zones preferentially located at neurite term inals as indicated by the lower probability of finding ''silent'' elec trode positions and an increased nicotinic receptor responsiveness whe n compared with the cell body. In agreement with these data we have ob served a preferential deposition of dopamine-beta-hydroxylase into the neurite terminal plasmalemma after stimulation of intact cells. These observations might be of interest since the differences in the distri bution of secretory ''spots'' between round and neurite emitting chrom affin cells could be used to study the molecular factors determining a ctive site localization.