Interaction between ryanodine receptor function and sarcolemmal Ca2+ currents.
We used the whole cell voltage-clamp technique to investigate the effects of disruption of Ca2+ release from the sarcoplasmic reticulum (SR) on sarcolemmal Ca2+ currents of chick myotubes kept in culture for 7 or 8 days. Ca2+ currents were recorded in 145 mM tetraethylammonium chloride and 10 mM Ca2+ with pipettes containing cesium and 10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. We found two components of Ca2+ current: 1) relatively large T-type currents that were activated near -50 mV and inactivated during 100-ms depolarizations to potentials positive to -60 mV (they were of similar magnitude in Ba2+ or Ca2+ and were insensitive to nifedipine) and 2) L-type currents that were activated near 0 mV and showed little or no inactivation during 100-ms depolarizations (they were larger when Ba2+ was the charge carrier and were blocked by 10 microM nifedipine). Addition of 1 or 100 microM ryanodine to the culture medium for 6-7 days caused a modest but significant increase in the L-type Ca2+ current density (pA/pF). Ryanodine (1 or 100 microM) exposure for 1-7 days reduced the T-type Ca2+ current density to < 10% of control. In contrast, exposure to 1 microM ryanodine for 0.5-3 h had no significant effect on either component of Ca2+ current. These data indicate that ryanodine has no direct action on Ca2+ currents in chick myotubes. However, disruption of SR Ca2+ release for > 24 h changes sarcolemmal Ca2+ channel expression or function.
Kenyon
J L
JL
Department of Physiology, University of Nevada School of Medicine, Reno 89557, USA.
McKemy
D D
DD
Airey
J A
JA
Sutko
J L
JL
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism* / Q000502:physiology*; D002642:Chick Embryo; D004553:Electric Conductivity; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000187:drug effects / Q000196:embryology; D009154:Mutation; D012016:Reference Values; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel; D012508:Sarcolemma / Q000502:physiology*
D015220:Calcium Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine