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 restri cted 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 immu noblotting, immunofluorescence, and RT-PCR. Amplifications of SNAP-25 mRNAs were combined with Southern hybridization, restriction enzyme analysis, an d sequencing of cloned PCR products to compare SNAP-25 isoform expression i n rat and bovine adrenal glands. SNAP-25 and SNAP-23 mRNA and protein are e xpressed in the glands; SNAP-23 is enriched in the adrenal cortex, whereas SNAP-25 is restricted to the adrenal medulla. Furthermore, high levels of S NAP-25 and low levels of SNAP-23 are observed in the PC12 cells, whereas bo th 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%), b ut 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 adr energic cells (93%) expressed a higher level of SNAP-25b (70%), suggesting that this isoform may not be restricted to fast neurotransmission.