Response of ryanodine receptor channels to Ca2+ steps produced by rapid solution exchange.
We used a flow method for Ca2+ activation of sheep cardiac and rabbit skeletal ryanodine receptor (RyR) channels in lipid bilayers, which activated RyRs in < 20 ms and maintained a steady [Ca2+] for 5 s. [Ca2+] was rapidly altered by flowing Ca(2+)-buffered solutions containing 100 or 200 microM Ca2+ from a perfusion tube inserted in the cis, myoplasmic chamber above the bilayer. During steps from 0.1 to 100 microM, [Ca2+] reached 0.3 microM (activation threshold) and 10 microM (maximum Po) in times consistent with predictions of a solution exchange model. Immediately following rapid RyR activation, Po was 0.67 (cardiac) and 0.45 (skeletal) at a holding voltage of +40 mV (cis/trans). Po then declined (at constant [Ca2+]) in 70% of channels (n = 25) with time constants ranging from .5 to 15 s. The mechanism for Po decline, whether it be adaptation or inactivation, was not determined in this study. cis, 2 mM Mg2+ reduced the initial Po for skeletal RyRs to 0.21 and marginally slowed the declining phase. During very rapid falls in [Ca2+] from mM (inhibited) to sub-microM (sub-activating) levels, skeletal RyR did not open. We conclude the RyR gates responsible for Ca(2+)-dependent activation and inhibition of skeletal RyRs can gate independently.
Laver
D R
DR
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australia. derek.laver@anu.edu.au
Curtis
B A
BA
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D015640:Ion Channel Gating; D007700:Kinetics; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D009124:Muscle Proteins / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009928:Organ Specificity; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000502:physiology; D012756:Sheep; D012996:Solutions
D015220:Calcium Channels; D002712:Chlorides; D008051:Lipid Bilayers; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D012996:Solutions; D002586:Cesium; C028019:cesium chloride; D002118:Calcium