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Updated: Feb 25, 2026

Monitoring Leucine-Rich Repeat Containing 8 Channel (LRRC8/VRAC) Activity Using Sensitized-Emission Förster Resonance Energy Transfer (SE-FRET)
Published on: August 9, 2024
Key role of segment IS4 in Cav1.2 inactivation: link between activation and inactivation
Stanislav Andranovits1, Stanislav Beyl2,3, Annette Hohaus1
1Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
Abstract:
Inactivation of L-type calcium channel (Cav1.2) is an important determinant of the length of the cardiac action potential. Here, we report a key role of the voltage-sensing segment IS4 in Cav1.2 inactivation. Neutralization of IS4 charges gradually shifted the steady-state inactivation curve on the voltages axis from 5.1 ± 3.7 mV in single point mutant IS4(K1Q) to -26.7 ± 1.3 mV in quadruple mutant IS4(K1Q/R2Q/R3Q/R4Q) compared to wild-type (WT) and accelerated inactivation. The slope factor of the Boltzmann curve of inactivation was decreased from 17.4 ± 3.5 mV (IS4(K1Q)) to 6.2 ± 0.7 mV (IS4(K1Q/R2Q/R3Q/R4Q)). Neutralizations of single or multiple charges in IIS4 and IIIS4 did not significantly affect the time course of inactivation. Neutralization of individual IVS4 charges shifted the inactivation curve between 17.4 ± 1.7 mV (IVS4(R2Q)) and -4.6 ± 1.4 mV (IVS4(R4Q)) on the voltage axis and affected the slope of the inactivation curves (IVS4(R2Q): 10.2 ± 1.2 mV, IVS4(R4Q): 9.7 ± 0.7 mV and IVS4(K5Q): 8.1 ± 0.7 mV vs WT: 14.1 ± 0.8 mV). IS4(K1Q) attenuated while IS4(K1Q/R2Q/R3Q) and IS4(K1Q/R2Q/R4Q/R3Q) enhanced the development of inactivation. Shifts in the voltage dependence of inactivation curves induced by IS4 neutralizations significantly correlated with shifts of the voltage dependence of channel activation (r = 0.95, p < 0.01) indicating that IS4 movement is not only rate limiting for activation but also initiates inactivation. The paradoxical decrease of the slope factor of the steady-state inactivation and acceleration of inactivation kinetics upon charge neutralization in segment IS4 may reflect the loss of stabilizing interactions of arginines and lysine with surrounding residues.
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