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.
Highlights
Calcium entry through voltage-gated calcium channels (Cav) mediates excitation of neuronal and muscle cells and triggers contraction, release of hormones and neurotransmitters, and many other key cellular processes [21, 34, 37]
Voltage-dependent inactivation of Cav1.2 develops during the plateau phase of the cardiac action potential (AP) and enables timed repolarization and tuned calcium entry
We investigate the role of S4 charges in voltage-dependent inactivation of Cav1.2
Summary
Calcium entry through voltage-gated calcium channels (Cav) mediates excitation of neuronal and muscle cells and triggers contraction, release of hormones and neurotransmitters, and many other key cellular processes [21, 34, 37]. Membrane depolarization causes Cav to open (activation) but induces channel closure, a process called inactivation. Voltage-dependent inactivation of Cav1.2 develops during the plateau phase of the cardiac action potential (AP) and enables timed repolarization and tuned calcium entry. Loss of inactivation may prolong the cardiac AP several times [3]. The consequences of a failure in inactivation are particular evident from the Timothy syndrome (TS). Prolongation of the cardiac AP in these patients is associated with prolongation of the QT interval, ventricular fibrillation, cardiac arrest, developmental abnormalities, and disorders of the central nervous system [31]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
