Characterization of two pathological gating-charge substitutions in Cav1.4 L-type calcium channels

ABSTRACT

Cav1.4 L-type calcium channels are predominantly expressed at the photoreceptor terminals and in bipolar cells, mediating neurotransmitter release. Mutations in its gene, CACNA1F, can cause congenital stationary night-blindness type 2 (CSNB2). Due to phenotypic variability in CSNB2, characterization of pathological variants is necessary to better determine pathological mechanism at the site of action. A set of known mutations affects conserved gating charges in the S4 voltage sensor, two of which have been found in male CSNB2 patients. Here, we describe two disease-causing Cav1.4 mutations with gating charge neutralization, exchanging an arginine 964 with glycine (RG) or arginine 1288 with leucine (RL). In both, charge neutralization was associated with a reduction channel expression also reflected in smaller ON gating currents. In RL channels, the strong decrease in whole-cell current densities might additionally be explained by a reduction of single-channel currents. We further identified alterations in their biophysical properties, such as a hyperpolarizing shift of the activation threshold and an increase in slope factor of activation and inactivation. Molecular dynamic simulations in RL substituted channels indicated water wires in both, resting and active, channel states, suggesting the development of omega (ω)currents as a new pathological mechanism in CSNB2. This sum of the respective channel property alterations might add to the differential symptoms in patients beside other factors, such as genomic and environmental deviations.

KEYWORDS:

• L-type calcium channels
• Cav1.4
• calcium channelopathies
• voltage sensor
• congenital stationary night blindness type 2

Acknowledgments

We thank Bettina Tschugg and Jenny Müller for their excellent technical support. We also thank Petronel Tuluc for a helpful scientific discussion. We thank Xuechen Tang for critical discussions and the support in interpreting data.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

All data generated or analyzed during this study are included in this published article (and its Supplementary Information files). The data that support the findings of this study are available from the corresponding author, AK, upon reasonable request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/19336950.2023.2192360

Additional information

Funding

This work was supported by the Austrian Science Fund (FWF P-32747 to AK, Doc 30 to AK, FWF-P34518 MF-Q), Tirolean Science Fund (TWF P7400-036-011 to LZ), the Austrian Academy of sciences APART-MINT postdoctoral fellowship to M.L.F.Q the Center for Molecular Biosciences Innsbruck (CMBI) and the University of Innsbruck.