Abstract
ABSTRACTThe voltage-gated calcium channel CaV1.1a primarily functions as voltage-sensor in skeletal muscle excitation-contraction (EC) coupling. In embryonic muscle the splice variant CaV1.1e, which lacks exon 29, additionally function as a genuine L-type calcium channel. Because previous work in most laboratories used a CaV1.1 expression plasmid containing a single amino acid substitution (R165K) of a critical gating charge in the first voltage-sensing domain (VSD), we corrected this substitution and analyzed its effects on the gating properties of the L-type calcium currents in dysgenic myotubes. Reverting K165 to R right-shifted the voltage-dependence of activation by ~12 mV in both CaV1.1 splice variants without changing their current amplitudes or kinetics. This demonstrates the exquisite sensitivity of the voltage-sensor function to changes in the specific amino acid side chains independent of their charge. Our results further indicate the cooperativity of VSDs I and IV in determining the voltage-sensitivity of CaV1.1 channel gating.
Highlights
The dihydropyridine (DHP) receptor functions as voltage-sensor in skeletal muscle excitationcontraction (EC) coupling and as a slowly activating calcium channel
Already the early work in dysgenic myotubes reconstituted with the rabbit CaV1.1 clone established the similarity of its biophysical properties with currents recorded in wildtype myotubes
Like calcium currents in native skeletal muscle cells, dysgenic myotubes reconstituted with pCAC6 displayed the characteristic slow activation kinetics, right-shifted voltage-dependence of activation, and relatively small current amplitudes [8]
Summary
The dihydropyridine (DHP) receptor functions as voltage-sensor in skeletal muscle excitationcontraction (EC) coupling and as a slowly activating calcium channel. It was the first member of the voltage-gated calcium channel family (CaV) that has been biochemically isolated [1], the first to be cloned [2], and the first pseudo-tetrameric cation channel for which the protein structure has been solved using cryo-electron microscopy [3]. With the recent discovery that coexpression of the scaffolding protein STAC3 allows functional expression of CaV1.1 in mammalian non-muscle cells and Xenopus oocyes [6,7], analysis of the CaV1.1 channel isoform has been opened to a considerably wider research community
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