| First Author | Idoux R | Year | 2020 |
| Journal | Cell Calcium | Volume | 91 |
| Pages | 102256 | PubMed ID | 32866694 |
| Mgi Jnum | J:319333 | Mgi Id | MGI:6863733 |
| Doi | 10.1016/j.ceca.2020.102256 | Citation | Idoux R, et al. (2020) Divalent cations permeation in a Ca(2+) non-conducting skeletal muscle dihydropyridine receptor mouse model. Cell Calcium 91:102256 |
| abstractText | In response to excitation of skeletal muscle fibers, trains of action potentials induce changes in the configuration of the dihydropyridine receptor (DHPR) anchored in the tubular membrane which opens the Ca(2+) release channel in the sarcoplasmic reticulum membrane. The DHPR also functions as a voltage-gated Ca(2+) channel that conducts L-type Ca(2+) currents routinely recorded in mammalian muscle fibers, which role was debated for more than four decades. Recently, to allow a closer look into the role of DHPR Ca(2+) influx in mammalian muscle, a knock-in (ki) mouse model (ncDHPR) carrying mutation N617D (adjacent to domain II selectivity filter E) in the DHPRalpha1S subunit abolishing Ca(2+) permeation through the channel was generated [Dayal et al., 2017]. In the present study, the Mn(2+) quenching technique was initially intended to be used on voltage-clamped muscle fibers from this mouse to determine whether Ca(2+) influx through a pathway distinct from DHPR may occur to compensate for the absence of DHPR Ca(2+) influx. Surprisingly, while N617D DHPR muscle fibers of the ki mouse do not conduct Ca(2+), Mn(2+) entry and subsequent quenching did occur because Mn(2+) was able to permeate and produce L-type currents through N617D DHPR. N617D DHPR was also found to conduct Ba(2+) and Ba(2+) currents were strongly blocked by external Ca(2+). Ba(2+) permeation was smaller, current kinetics slower and Ca(2+) block more potent than in wild-type DHPR. These results indicate that residue N617 when replaced by the negatively charged residue D is suitably located at entrance of the pore to trap external Ca(2+) impeding in this way permeation. Because Ba(2+) binds with lower affinity to D, Ba(2+) currents occur, but with reduced amplitudes as compared to Ba(2+) currents through wild-type channels. We conclude that mutations located outside the selectivity filter influence channel permeation and possibly channel gating in a fully differentiated skeletal muscle environment. |
