Orthograde dihydropyridine receptor signal regulates ryanodine receptor passive leak

• Published in: Proceedings of the National Academy of Sciences - PNAS 2011-04, Vol.108 (17), p.7046-7051
• Main Authors: Eltit, José Miguel, Li, Hongli, Ward, Christopher W, Molinski, Tadeusz, Pessah, Isaac N, Allen, Paul D, Lopez, José R
• Format: Article
• Language: English
• Subjects: Animals; Biological Sciences; Calcium; Calcium - metabolism; Calcium Channels, L-Type - genetics; Calcium Channels, L-Type - metabolism; Calcium Signaling - drug effects; Calcium Signaling - physiology; Cells; Dihydropyridines; Fluorescence; Halogenated Diphenyl Ethers - pharmacology; Homeostasis; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Malignant hyperthermia; Mice; Mice, Mutant Strains; muscle contraction; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle fibers; Muscle Fibers, Skeletal - cytology; Muscle Fibers, Skeletal - metabolism; muscles; Musculoskeletal system; myotubes; Physiological regulation; Physiology; Proteins; Receptors; Ryanodine Receptor Calcium Release Channel - genetics; Ryanodine Receptor Calcium Release Channel - metabolism; Sarcolemma - genetics; Sarcolemma - metabolism; Sarcoplasmic reticulum; Signal transduction; Skeletal muscle
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1018380108

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 CaV1.1 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 Ca²⁺-selective microelectrodes, we demonstrate that the lack of CaV1.1 expression was associated with an increased myoplasmic resting [Ca²⁺] ([Ca²⁺]rest), increased resting sarcolemmal Ca²⁺ entry, and decreased sarcoplasmic reticulum (SR) Ca²⁺ loading. Pharmacological control of the RyR1 leak state, using bastadin 5, reverted the three parameters to WT levels. The fact that Ca²⁺ 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 [Ca²⁺]rest and the SR Ca²⁺ content in the physiological range and thus maintain normal intracellular Ca²⁺ homeostasis.