Calcium signal-mediated expression of the vasoactive intestinal polypeptide gene and its small contribution to activity-dependent survival of mouse cerebellar granule cells

We have demonstrated previously in primary cultures of mouse cerebellar granule cells (CGCs) that endogenously synthesized pituitary adenylate cyclase-activating polypeptide (PACAP) contributes at least in part to the activity-dependent survival of CGCs (Tabuchi et al. [2001] Neurosci. Res. 39:85-93). In this study, we have demonstrated that expression of vasoactive intestinal polypeptide (VIP), a member of the same VIP/secretin/glucagon family as PACAP, was activated markedly by Ca²⁺ influx through L-type voltage-dependent Ca²⁺ channels (L-VDCCs), which could be induced under the depolarizing condition induced by high concentration of potassium (K⁺) in the medium. The activation of VIP mRNA expression, different from that of PACAP, was dependent partly on de novo protein synthesis. On the other hand, mRNA expression of secretin and PACAP/VIP receptors (PAC ₁, VPAC₁, and VPAC₂) was not activated by the Ca²⁺ influx; rather, PAC₁ mRNA expression was reduced. Exogenously added VIP prevented apoptosis of CGCs under nondepolarizing conditions, the effect of which was mediated specifically through the VPAC ₁ receptor. Furthermore, the survival of CGCs under depolarizing conditions could be mediated partly through VPAC₁, the contribution of which was much less than that of PAC₁. These findings indicate that PACAP and VIP genes are coordinately activated by the Ca²⁺ signals in CGCs, but the contribution of VIP to the activity-dependent survival of CGCs is quite small.