Elevated resting [Ca(2+)](i) in myotubes expressing malignant hyperthermia RyR1 cDNAs is partially restored by modulation of passive calcium leak from the SR.
Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle triggered in susceptible individuals by inhalation anesthetics and depolarizing skeletal muscle relaxants. This syndrome has been linked to a missense mutation in the type 1 ryanodine receptor (RyR1) in more than 50% of cases studied to date. Using double-barreled Ca(2+) microelectrodes in myotubes expressing wild-type RyR1 ((WT)RyR1) or RyR1 with one of four common MH mutations ((MH)RyR1), we measured resting intracellular Ca(2+) concentration ([Ca(2+)](i)). Changes in resting [Ca(2+)](i) produced by several drugs known to modulate the RyR1 channel complex were investigated. We found that myotubes expressing any of the (MH)RyR1s had a 2.0- to 3.7-fold higher resting [Ca(2+)](i) than those expressing (WT)RyR1. Exposure of myotubes expressing (MH)RyR1s to ryanodine (500 microM) or (2,6-dichloro-4-aminophenyl)isopropylamine (FLA 365; 20 microM) had no effects on their resting [Ca(2+)](i). However, when myotubes were exposed to bastadin 5 alone or to a combination of ryanodine and bastadin 5, the resting [Ca(2+)](i) was significantly reduced (P < 0.01). Interestingly, the percent decrease in resting [Ca(2+)](i) in myotubes expressing (MH)RyR1s was significantly greater than that for (WT)RyR1. From these data, we propose that the high resting myoplasmic [Ca(2+)](i) in (MH)RyR1 expressing myotubes is due in part to a related structural conformation of (MH)RyR1s that favors "passive" calcium leak from the sarcoplasmic reticulum.
Yang
Tianzhong
T
Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115, USA.
Esteve
Eric
E
Pessah
Isaac N
IN
Molinski
Tadeusz F
TF
Allen
Paul D
PD
López
José R
JR
D000494:Allosteric Regulation; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D018076:DNA, Complementary; D055768:Halogenated Diphenyl Ethers; D006801:Humans; D017736:Ion-Selective Electrodes; D008305:Malignant Hyperthermia / Q000235:genetics / Q000378:metabolism*; D008839:Microelectrodes; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009154:Mutation; D010627:Phenethylamines / Q000494:pharmacology; D010647:Phenyl Ethers / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D014162:Transfection
D018076:DNA, Complementary; D055768:Halogenated Diphenyl Ethers; D010627:Phenethylamines; D010647:Phenyl Ethers; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; C060909:FLA 365; C105188:bastadin 5; D002118:Calcium