Chloride-dependent sarcoplasmic reticulum Ca2+ release correlates with increased Ca2+ activation of ryanodine receptors.
The mechanism by which chloride increases sarcoplasmic reticulum (SR) Ca2+ permeability was investigated. In the presence of 3 microM Ca2+, Ca2+ release from 45Ca(2+)-loaded SR vesicles prepared from procine skeletal muscle was increased approximately 4-fold when the media contained 150 mM chloride versus 150 mM propionate, whereas in the presence of 30 nM Ca2+, Ca2+ release was similar in the chloride- and the propionate-containing media. Ca(2+)-activated [3H]ryanodine binding to skeletal muscle SR was also increased (2- to 10-fold) in media in which propionate or other organic anions were replaced with chloride; however, chloride had little or no effect on cardiac muscle SR 45Ca2+ release or [3H]ryanodine binding. Ca(2+)-activated [3H]ryanodine binding was increased approximately 4.5-fold after reconstitution of skeletal muscle RYR protein into liposomes, and [3H]ryanodine binding to reconstituted RYR protein was similar in chloride- and propionate-containing media, suggesting that the sensitivity of the RYR protein to changes in the anionic composition of the media may be diminished upon reconstitution. Together, our results demonstrate a close correlation between chloride-dependent increases in SR Ca2+ permeability and increased Ca2+ activation of skeletal muscle RYR channels. We postulate that media containing supraphysiological concentrations of chloride or other inorganic anions may enhance skeletal muscle RYR activity by favoring a conformational state of the channel that exhibits increased activation by Ca2+ in comparison to the Ca2+ activation exhibited by this channel in native membranes in the presence of physiological chloride (< or = 10 mM). Transitions to this putative Ca(2+)-activatable state may thus provide a mechanism for controlling the activation of RYR channels in skeletal muscle.
Fruen
B R
BR
Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108, USA. fruen001@maroon.tc.umn.edu
Kane
P K
PK
Mickelson
J R
JR
Louis
C F
CF
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D002451:Cell Compartmentation; D002474:Cell-Free System; D002712:Chlorides / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D008081:Liposomes; D009124:Muscle Proteins / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology* / Q000648:ultrastructure; D009206:Myocardium / Q000648:ultrastructure; D009566:Nitrates / Q000494:pharmacology; D010472:Perchlorates / Q000494:pharmacology; D012433:Ryanodine / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000502:physiology*; D013552:Swine
D015220:Calcium Channels; D002712:Chlorides; D008081:Liposomes; D009124:Muscle Proteins; D009566:Nitrates; D010472:Perchlorates; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D002118:Calcium