o-Phthalaldehyde activates the Ca(2+) release mechanism from skeletal muscle sarcoplasmic reticulum.
o-Phthalaldehyde (OPA) is a bifunctional reagent that forms an isoindole derivative by reacting with cysteine and lysine residues separated by approximately 0.3 nm. OPA inhibits sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity at low micromolar concentrations and induces Ca(2+) release from actively loaded SR vesicles by activating the ryanodine receptor from fast twitch skeletal muscle. Both ryanodine binding and single-channel activity show a biphasic concentration dependence. At low OPA concentrations (<100 microM), ryanodine binding and single channel activity are stimulated, while at higher concentrations, a time-dependent sequential activation and inhibition of receptor binding is observed. Activation is characterized by a Ca(2+)-independent increase in maximal receptor occupancy. Data are presented to support a model in which Ca(2+) channel and ryanodine binding activity are enhanced due to an intramolecular cross-linking of nearby lysine and nonhyperreactive cysteine residues. OPA complexation with endogenous lysine residue(s) is critical for receptor activation.
Abramson
J J
JJ
Department of Physics, Portland State University, Portland, Oregon 97207, USA. abramson@pdx.edu
Mullen
S P
SP
Koehler
S
S
Mansoor
D
D
Anderson
P
P
Wamser
C C
CC
Swan
T J
TJ
Favero
T G
TG
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D012433:Ryanodine / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium; D009764:o-Phthalaldehyde / Q000494:pharmacology*
D014316:Tritium; D012433:Ryanodine; D009764:o-Phthalaldehyde; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium