The β_1a subunit regulates the functional properties of adult frog and mouse L‐type Ca²⁺ channels of skeletal muscle

Abstract

The β1a subunit, one of the auxiliary subunits of CaV1.1 channels, was expressed in COS‐1 cells, purified by electroelution and electrodialysis techniques and identified by Western blot using monoclonal antibodies. The purified β1a subunit strongly interacted in vitro with the alpha interaction domain (AID) of CaV1.1 channels. The actions of the purified β1a subunit on CaV1.1 channel currents were assessed in whole cell voltage clamp experiments performed in vesicles derived from frog and mouse adult skeletal muscle plasma membranes. L‐type inward currents were recorded in solutions containing Ba2+ (IBa). Values of peak IBa were doubled by the β1a subunit in frog and mouse muscle vesicles and the amplitude of the slow component of tail currents was greatly increased. The actions of the β1a subunit on CaV1.1 channel currents reached a steady state within 20 min. The β1a subunit had no effect on the time courses of activation or inactivation of IBa or shifted the current‐voltage relation. Non‐linear capacitive currents were recorded in solutions that contained mostly impermeant ions. Charge movement depended on voltage with average Boltzmann parameters: Qmax+ 28.0 ± 6.6 nC μF−1, V+−58.0 ± 2.0 mV and k+ 15.3± 1.1 mV (n= 24). In the presence of the β1a subunit, these parameters remained unchanged: Qmax+ 29.8 ± 3.5 nC μF−1, V+−54.5 ± 2.2 mV and k+ 16.4± 1.3 mV (n= 21). Overall, the work describes a novel preparation to explore in situ the role of the β1a subunit on the function of adult CaV1.1 channels.

Regulation of voltage-gated calcium channel activity by the Rem and Rad GTPases

“…4), although it is possible that muscle-specific proteins may stabilize the complex or that yet-to-be-defined posttranslational modification(s) or GTP binding may stabilize a higher-affinity complex. In parallel, Ca V ␤ regulation of Ca V ␣ is a dynamic process that may involve transient association of preformed channels in the surface membrane (29). This information, coupled with our finding that Rem and Rad potently inhibit L type but not heterologously expressed T type Ca 2ϩ channels (Fig.…”

Molecular Dissection of the Hydrophobic Segments H3 and H4 of the Yeast Ca2+ Channel Component Mid1

“…The other hypothesis is that Mid1 might form no channel by itself and instead be a regulatory subunit protein of a Ca 2ϩ channel whose pore-forming subunit is Cch1. It is known that mammalian voltage-gated Ca 2ϩ channels have auxiliary subunits, ␣2␦, ␤, and ␥, which regulate the activity of the pore-forming ␣1 subunit homologous to Cch1 (12)(13)(14)(15)(16). Because the structure of the putative Ca 2؉ channel(s) composed of Mid1 and Cch1 is an open question at present, we would like to explain the data presented in this paper from the viewpoint of both hypotheses.…”

“…The voltage-gated Ca 2ϩ channels are heteromultimeric proteins consisting of ␣1, cytoplasmic ␤, and nonpore-forming transmembrane ␣2␦ and ␥ subunits (11). These non-pore-forming subunits dramatically influence the properties and surface expression of the channels (12)(13)(14)(15)(16). Although the channel activity of Cch1 has not yet been revealed experimentally and Mid1 has no homology to the auxiliary subunits, Mid1 has been shown to cooperate with Cch1 in mating pheromone-induced Ca 2ϩ uptake (8,9,17), store-operated or capacitative Ca 2ϩ entry (10), endoplasmic reticulum stress-induced Ca 2ϩ uptake (18), and a hyperosmotic stress-induced increase in cytosolic Ca 2ϩ (19).…”

The junctional SR protein JP-45 affects the functional expression of the voltage-dependent Ca2+ channel Cav1.1

“…Fig. 10 (Garcia et al, 2002;Jones et al, 2002). The I-II loop is adjacent to a repeat within the ␣1.1 subunit domain involved in channel gating.…”