SNAP-25 is differentially expressed by noradrenergic and adrenergic chromaffin cells

This study examines chromaffin cell expression of the synaptosomal-associated protein SNAP-25 in the adrenal medulla by immunoblotting, immunocytochemistry and PCR. Both mRNAs coding for the SNAP-25 isoforms a and b were detected and SNAP-25 was found to be present in all chromaffin cells in adult rat adrenal gland sections. It was essentially restricted to a zone close to the cytoplasmic face of the plasma membrane in the majority of cells, but located extensively throughout the cytoplasm in a chromaffin cell sub-population, identified by double immunofluorescence labelling to have a noradrenergic phenotype. This differential SNAP-25 expression may reflect different stages in the phenotypic development of the sympathoadrenal lineage and be related to an additional functional role in noradrenergic chromaffin cells not associated with secretion.