Dynamic but not constitutive association of calmodulin with rat TRPV6 channels enables fine tuning of Ca2+‐dependent inactivation
- 8 November 2006
- journal article
- Published by Wiley in The Journal of Physiology
- Vol. 577 (1), 31-44
- https://doi.org/10.1113/jphysiol.2006.118661
Abstract
The Ca2+-selective TRPV6 as well as the L-type Ca2+ channel are regulated by the Ca2+-binding protein calmodulin (CaM). Here, we investigated the interaction of CaM with rat (r)TRPV6 in response to alterations of intracellular Ca2+, employing Ca2+-imaging and patch-clamp techniques. Additionally, confocal Förster resonance energy transfer (FRET) microscopy on living cells was utilized as a key method to visualize in vivo protein–protein interactions essential for CaM regulation of rTRPV6 activity. The effects of overexpressed CaM or its Ca2+-insensitive mutant (CaMMUT) was probed on various rTRPV6 mutants and fragments in an attempt to elucidate the molecular mechanism of Ca2+/CaM-dependent regulation and to pinpoint the physiologically relevant rTRPV6–CaM interaction site. A significant reduction of rTRPV6 activity, as well as an increase in current inactivation, were observed when CaM was overexpressed in addition to endogenous CaM. The Ca2+-insensitive CaMMUT, however, failed to affect rTRPV6-derived currents. Accordingly, live cell confocal FRET microscopy revealed a robust interaction for CaM but not CaMMUT with rTRPV6, suggesting a strict Ca2+ dependence for their association. Indeed, interaction of rTRPV6 or its C terminus with CaM increased with rising intracellular Ca2+ levels, as observed by dynamic FRET measurements. An rTRPV6Δ695–727 mutant with the very C-terminal end deleted, yielded Ca2+ currents with a markedly reduced inactivation in accordance with a lack of CaM interaction as substantiated by FRET microscopy. These results, in contrast with those for CaM-dependent L-type Ca2+ channel inactivation, demonstrate a dynamic association of CaM with the very C-terminal end of rTRPV6 (aa 695–727), and this enables acceleration of the rate of rTRPV6 current inactivation with increasing intracellular CaM concentrations.This publication has 40 references indexed in Scilit:
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