Differential Expression of SNAP‐25 Isoforms and SNAP‐23 in the Adrenal Gland

: In the rat adrenal gland, we previously observed that SNAP‐25 is not restricted to the plasmalemma in noradrenergic cells as it is in adrenergic cells, and hypothesized that SNAP‐25 isoform expression is different in the two phenotypes. Expression of SNAP‐25 isoforms and SNAP‐23 was examined by immunoblotting, immunofluorescence, and RT‐PCR. Amplifications of SNAP‐25 mRNAs were combined with Southern hybridization, restriction enzyme analysis, and sequencing of cloned PCR products to compare SNAP‐25 isoform expression in rat and bovine adrenal glands. SNAP‐25 and SNAP‐23 mRNA and protein are expressed in the glands ; SNAP‐23 is enriched in the adrenal cortex, whereas SNAP‐25 is restricted to the adrenal medulla. Furthermore, high levels of SNAP‐25 and low levels of SNAP‐23 are observed in the PC12 cells, whereas both SNAP‐25 and SNAP‐23 are expressed in adrenal medullary cultures. In all extracts, the SNAP‐23 mRNA corresponded to SNAP‐23a. SNAP‐25a is the major form expressed in rat adrenal glands (75%), as it is in PC12 cells (80%), but both SNAP‐25a and SNAP‐25b (40% vs. 60%) are expressed in bovine adrenal medulla in situ and in culture. In addition, an enriched population of adrenergic cells (93%) expressed a higher level of SNAP‐25b (70%), suggesting that this isoform may not be restricted to fast neurotransmission.