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Ca(2+) channel inactivation heterogeneity reveals physiological unbinding of auxiliary beta subunits
S Restituito1, T Cens, M Rousset
1CRBM, CNRS UPR 1086, UFR 24, 34293 Montpellier Cedex 05, France.
Abstract:
Voltage gated Ca(2+) channel (VGCC) auxiliary beta subunits increase membrane expression of the main pore-forming alpha(1) subunits and finely tune channel activation and inactivation properties. In expression studies, co-expression of beta subunits also reduced neuronal Ca(2+) channel regulation by heterotrimeric G protein. Biochemical studies suggest that VGCC beta subunits and G protein betagamma can compete for overlapping interaction sites on VGCC alpha(1) subunits, suggesting a dynamic association of these subunits with alpha(1). In this work we have analyzed the stability of the alpha(1)/beta association under physiological conditions. Regulation of the alpha(1A) Ca(2+) channel inactivation properties by beta(1b) and beta(2a) subunits had two major effects: a shift in voltage-dependent inactivation (E(in)), and an increase of the non-inactivating current (R(in)). Unexpectedly, large variations in magnitude of the effects were recorded on E(in), when beta(1b) was expressed, and R(in), when beta(2a) was expressed. These variations were not proportional to the current amplitude, and occurred at similar levels of beta subunit expression. beta(2a)-induced variations of R(in) were, however, inversely proportional to the magnitude of G protein block. These data underline the two different mechanisms used by beta(1b) and beta(2a) to regulate channel inactivation, and suggest that the VGCC beta subunit can unbind the alpha1 subunit in physiological situations.
Insights
Voltage-gated calcium channel (VGCC) beta subunits modulate channel function. This study shows beta subunits can detach from alpha1 subunits under physiological conditions, revealing distinct regulatory mechanisms for inactivation.
Area of Science:
- Neuroscience
- Molecular Biology
- Biophysics
Background:
- Voltage-gated calcium channels (VGCCs) are crucial for neuronal function.
- Auxiliary beta (β) subunits regulate VGCC trafficking and gating.
- β subunits are known to interact with G protein subunits, influencing channel modulation.
Purpose of the Study:
- To investigate the stability of the interaction between VGCC α1 and β subunits under physiological conditions.
- To elucidate the distinct mechanisms by which different β subunits (β1b and β2a) regulate channel inactivation.
- To explore the relationship between β subunit association, G protein modulation, and channel inactivation.
Main Methods:
- Co-expression of VGCC α1A and specific β subunits (β1b, β2a) in expression studies.
- Analysis of voltage-dependent inactivation (Ein) and non-inactivating current (Rin).
- Assessment of G protein block magnitude and its relation to β subunit effects.
Main Results:
- β1b and β2a subunits differentially regulated α1A channel inactivation, affecting Ein and Rin.
- Variations in the magnitude of these effects were observed and not proportional to current amplitude.
- β2a-induced changes in Rin were inversely related to the extent of G protein block.
Conclusions:
- VGCC β subunits exhibit distinct inactivation regulation mechanisms via β1b and β2a.
- The association between VGCC β and α1 subunits is dynamic and can be transient under physiological conditions.
- These findings suggest β subunits can unbind from α1 subunits, impacting channel function and modulation.