Low serum promotes maturation of excitation-contraction coupling in myotubes.
Patch-clamping and the simultaneous fluorescence measurement of cytoplasmic Ca2+ ([Ca2+]i) were used to analyze the effect of serum on the functional features of excitation-contraction (E-C) coupling in mouse skeletal myotubes. In high-serum-treated (10%) myotubes, depolarization elicited Ca2+ release which continued for tens of milliseconds following the end of the pulse, after which [Ca2+]i decayed slowly. In low-serum-treated (0.5%) myotubes, the Ca2+ transient caused by depolarization had an increased rate of rise and peak amplitude, and [Ca2+]i began to decay rapidly upon repolarization. When a depolarizing pulse (0.5-1.0 s) was applied to low-serum-treated myotubes during a Ca2+ transient induced by 5-10 mM caffeine, repolarization usually caused the caffeine transient to terminate rapidly (RISC; repolarization-induced stop of caffeine-induced Ca2+ release). The RISC was less prominent in high-serum-treated myotubes. These results suggest that low serum promotes the maturation of myotubes so that Ca(2+)-release and Ca(2+)-removal activities are accelerated. Additionally, the essential features of the communication between the voltage sensor and the Ca(2+)-release channel are shared by myotubes and adult muscle fibers.
Suda
N
N
Department of Anatomy and Neurobiology, Colorado State University, Fort Collins 80523, USA.
Dirksen
R T
RT
Gonzalez
A
A
Beam
K G
KG
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001798:Blood Proteins / Q000494:pharmacology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics; D020746:Calcium Channels, L-Type / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D009119:Muscle Contraction / Q000187:drug effects*; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology
D001798:Blood Proteins; D020746:Calcium Channels, L-Type; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D002118:Calcium