CaV1.3 ion channels are dominant Ca(2+) portals into pacemaking neurons, residing at the epicenter of brain rhythmicity and neurodegeneration. Negative Ca(2+) feedback regulation of CaV1.3 channels (CDI) is therefore critical for Ca(2+) homeostasis. Intriguingly, nearly half the CaV1.3 transcripts in the brain are RNA edited to reduce CDI and influence oscillatory activity. It is then mechanistically remarkable that this editing occurs precisely within an IQ domain, whose interaction with Ca(2+)-bound calmodulin (Ca(2+)/CaM) is believed to induce CDI. Here, we sought the mechanism underlying the altered CDI of edited channels. Unexpectedly, editing failed to attenuate Ca(2+)/CaM binding. Instead, editing weakened the prebinding of Ca(2+)-free CaM (apoCaM) to channels, which proves essential for CDI. Thus, editing might render CDI continuously tunable by fluctuations in ambient CaM, a prominent effect we substantiate in substantia nigral neurons. This adjustability of Ca(2+) regulation by CaM now looms as a key element of CNS Ca(2+) homeostasis.
Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.