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Updated: Aug 6, 2026

Single-Cell Calcium Imaging for Studying the Activation of Calcium Ion Channels
Published on: December 13, 2024
C-terminal modulator controls Ca2+-dependent gating of Ca(v)1.4 L-type Ca2+ channels
Anamika Singh1, Daniel Hamedinger, Jean-Charles Hoda
1Abteilung Pharmakologie und Toxikologie, Institut für Pharmazie und Centrum für Molekulare Biowissenschaften Innsbruck, Universität Innsbruck, Peter-Mayrstr. 1/I, A-6020 Innsbruck, Austria.
Abstract:
Tonic neurotransmitter release at sensory cell ribbon synapses is mediated by calcium (Ca2+) influx through L-type voltage-gated Ca2+ channels. This tonic release requires the channels to inactivate slower than in other tissues. Ca(v)1.4 L-type voltage-gated Ca2+ channels (LTCCs) are found at high densities in photoreceptor terminals, and alpha1 subunit mutations cause human congenital stationary night blindness type-2 (CSNB2). Ca(v)1.4 voltage-dependent inactivation is slow and Ca2+-dependent inactivation (CDI) is absent. We show that removal of the last 55 or 122 (C122) C-terminal amino acid residues of the human alpha1 subunit restores calmodulin-dependent CDI and shifts voltage of half-maximal activation to more negative potentials. The C terminus must therefore form part of a mechanism that prevents calmodulin-dependent CDI of Ca(v)1.4 and controls voltage-dependent activation. Fluorescence resonance energy transfer experiments in living cells revealed binding of C122 to C-terminal motifs mediating CDI in other Ca2+ channels. The absence of this modulatory mechanism in the CSNB2 truncation mutant K1591X underlines its importance for normal retinal function in humans.
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