Embryonic chicken skeletal muscle cells fail to develop normal excitation-contraction coupling in the absence of the alpha ryanodine receptor. Implications for a two-ryanodine receptor system.
Two ryanodine receptor (RyR), sarcoplasmic reticulum Ca2+ release channels, alpha and beta, co-exist in chicken skeletal muscles. To investigate a two-RyR Ca2+ release system, we compared electrically evoked Ca2+ transients in Crooked Neck Dwarf (cn/cn) cultured muscle cells, which do not make alpha RyR, and normal (+/?) cells. At day 3 in culture, Ca2+ release in +/? cells required extracellular Ca2+ (Ca2+o), and Ca2+ transients had slow kinetics. At day 5, Ca2+ release was Ca2+o-independent in 40% of the cells, and transients were more rapid. By day 7, all +/? cells had Ca2+o-independent Ca2+ release. Contractions were observed in +/? cells on all days. Ca2+ transients were observed in cn/cn cells on days 3, 5, and 7, but in each case they were Ca2+o-dependent and exhibited slow kinetics. Localized vesiculations, not contractions, occurred in cn/cn cells. By day 10, Ca2+ transients were no longer observed in cn/cn cells even in Ca2+o. Sarcoplasmic reticulum Ca2+ was not depleted, as caffeine induced Ca2+ transients. Thus, in the absence of alpha RyR there is a failure to develop Ca2+o-independent Ca2+ release and contractions and to sustain Ca2+o-dependent release. Moreover, contributions by the alpha RyR cannot be duplicated by the beta RyR alone.
Ivanenko
A
A
Department of Pharmacology, University of Nevada School of Medicine, Reno 89557.
McKemy
D D
DD
Kenyon
J L
JL
Airey
J A
JA
Sutko
J L
JL
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D002455:Cell Division; D002470:Cell Survival; D002478:Cells, Cultured; D002642:Chick Embryo; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000196:embryology / Q000502:physiology*; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium