Chicken skeletal muscle ryanodine receptor isoforms: ion channel properties.
To define the roles of the alpha- and beta-ryanodine receptor (RyR) (sarcoplasmic reticulum Ca2+ release channel) isoforms expressed in chicken skeletal muscles, we investigated the ion channel properties of these proteins in lipid bilayers. alpha- and beta RyRs embody Ca2+ channels with similar conductances (792, 453, and 118 pS for K+, Cs+ and Ca2+) and selectivities (PCa2+/PK+ = 7.4), but the two channels have different gating properties. alpha RyR channels switch between two gating modes, which differ in the extent they are activated by Ca2+ and ATP, and inactivated by Ca2+. Either mode can be assumed in a spontaneous and stable manner. In a low activity mode, alpha RyR channels exhibit brief openings (tau o = 0.14 ms) and are minimally activated by Ca2+ in the absence of ATP. In a high activity mode, openings are longer (tau o1-3 = 0.17, 0.51, and 1.27 ms), and the channels are activated by Ca2+ in the absence of ATP and are in general less sensitive to the inactivating effects of Ca2+. beta RyR channel openings are longer (tau 01-3 = 0.34, 1.56, and 3.31 ms) than those of alpha RyR channels in either mode. beta RyR channels are activated to a greater relative extent by Ca2+ than ATP and are inactivated by millimolar Ca2+ in the absence, but not the presence, of ATP. Both alpha- and beta RyR channels are activated by caffeine, inhibited by Mg2+ and ruthenium red, inactivated by voltage (cytoplasmic side positive), and modified to a long-lived substate by ryanodine, but only alpha RyR channels are activated by perchlorate anions. The differences in gating and responses to channel modifiers may give the alpha- and beta RyRs distinct roles in muscle activation.
Percival
A L
AL
Department of Pharmacology, University of Nevada School of Medicine, Reno 89557.
Williams
A J
AJ
Kenyon
J L
JL
Grinsell
M M
MM
Airey
J A
JA
Sutko
J L
JL
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002645:Chickens; D004553:Electric Conductivity; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008861:Microsomes / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology; D009124:Muscle Proteins / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D007473:Ion Channels; D008051:Lipid Bilayers; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D000255:Adenosine Triphosphate; D002118:Calcium