The β3 subunit: a key regulator of vascular calcium channel expression (1057.10)

The pore-forming α1C subunit of the vascular L-type Ca2+ (CaL) channels upregulates during hypertension, which may contribute to increased arterial tone. Recently we reported that a small subunit of the CaL channel, β3, is required for the upregulation of vascular CaL channels and the development of hypertension. Here, we begin to explore the hypothesis that the CaL channel α1C subunit is subjected to rapid proteasomal degradation in VSMCs, but during hypertension, β3 rescues α1C from degradation to increase CaL channel abundance. Western blots (WB) of cultured A7r5 aortic VSMCs treated with β3 morpholino antisense (0.5 and 1 µg/ml) for 48 hr revealed a loss of the CaL channel α1C pore. Subsequently α1C band was detected in A7r5 cells on an anti-ubiquitin WB and blockade of proteasomal degradation by MG132 (1-10 µg/ml) for 18 hr increased CaL channel expression by 2-fold. Since chloroquine (100-200 μM), an inhibitor of lysosomal degradation, did not alter CaL channel expression after 24hr suggesting that CaL channel half-life (t1/2) is primarily determined by proteosomal degradation in A7r5 VSMCs. We also designed a new method to study the t1/2 of CaL channels in vivo, which indicated α1C is rapidly degraded with a t1/2 of ~3 hr in mesenteric arteries of normotensive rats. Future studies are designed to define the degradation pathway of vascular CaL channels in vivo and identify possible abnormalities in hypertension.