title: Orthograde dihydropyridine receptor signal regulates ryanodine receptor passive leak.
abstract: The skeletal muscle dihydropyridine receptor (DHPR) and ryanodine receptor (RyR1) are known to engage a form of conformation coupling essential for muscle contraction in response to depolarization, referred to as excitation-contraction coupling. Here we use WT and Ca(V)1.1 null (dysgenic) myotubes to provide evidence for an unexplored RyR1-DHPR interaction that regulates the transition of the RyR1 between gating and leak states. Using double-barreled Ca(2+)-selective microelectrodes, we demonstrate that the lack of Ca(V)1.1 expression was associated with an increased myoplasmic resting [Ca(2+)] ([Ca(2+)](rest)), increased resting sarcolemmal Ca(2+) entry, and decreased sarcoplasmic reticulum (SR) Ca(2+) loading. Pharmacological control of the RyR1 leak state, using bastadin 5, reverted the three parameters to WT levels. The fact that Ca(2+) sparks are not more frequent in dysgenic than in WT myotubes adds support to the hypothesis that the leak state is a conformation distinct from gating RyR1s. We conclude from these data that this orthograde DHPR-to-RyR1 signal inhibits the transition of gated RyR1s into the leak state. Further, it suggests that the DHPR-uncoupled RyR1 population in WT muscle has a higher propensity to be in the leak conformation. RyR1 leak functions are to keep [Ca(2+)](rest) and the SR Ca(2+) content in the physiological range and thus maintain normal intracellular Ca(2+) homeostasis.
authors.affiliation: Department of Anesthesiology, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: José Miguel
authors.initials: JM
authors.lastname: Eltit
authors.forename: Hongli
authors.initials: H
authors.lastname: Li
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Ward
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Molinski
authors.forename: Isaac N
authors.initials: IN
authors.lastname: Pessah
authors.forename: Paul D
authors.initials: PD
authors.lastname: Allen
authors.forename: José R
authors.initials: JR
authors.lastname: Lopez
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D055768:Halogenated Diphenyl Ethers / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D012508:Sarcolemma / Q000235:genetics / Q000378:metabolism*
chemical_list: C529218:CACNA1S protein, mouse; D020746:Calcium Channels, L-Type; D055768:Halogenated Diphenyl Ethers; D019837:Ryanodine Receptor Calcium Release Channel; C105188:bastadin 5; D002118:Calcium