Regulation of the purified Ca2+ release channel/ryanodine receptor complex of skeletal muscle sarcoplasmic reticulum by luminal calcium.
45Ca2+ flux and single channel measurements have related that the Ca2+ release channel/ryanodine receptor complex of striated muscle is regulated by micromolar cytoplasmic Ca2+. The effect of luminal Ca2+, however, remains controversial. In the experiments presented here, we reconstituted the isolated Ca2+ release channel of rabbit skeletal muscle sarcoplasmic reticulum into planar lipid bilayers in the presence of symmetrical K+ solutions. Using K+ as the charge carrier, we were able to examine the effect of changes in luminal calcium in the micro- to millimolar range. In the presence of activating cytoplasmic Ca2+, the release channel was activated and inactivated in a concentration-dependent manner by luminal Ca2+. Since increasing cytoplasmic EGTA concentrations shifted the dependence of channel open probability on luminal Ca2+ to higher Ca2+ concentrations, it is suggested that luminal Ca2+ exerts ist regulating effect by acting on Ca2+ binding sites accessible from the cytoplasmic side of the channel.
Herrmann-Frank
A
A
Department of Applied Physiology, University of Ulm, D-89069 Ulm, Germany.
Lehmann-Horn
F
F
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D015640:Ion Channel Gating; D008051:Lipid Bilayers; D009124:Muscle Proteins / Q000378:metabolism*; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012996:Solutions
D015220:Calcium Channels; D008051:Lipid Bilayers; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D012996:Solutions; D004533:Egtazic Acid; D011188:Potassium; D002118:Calcium