Calcium action potential and prolonged afterhyperpolarization in developing myotubes of a mouse clonal myogenic cell line.
Under a high-Ca condition (greater than 5 mM), myotubes of a mouse myogenic cell line MC3T3-A1/M13 generated a long-lasting Ca action potential and a prolonged afterhyperpolarization (a.h.p.) during their in vitro development. The action potential was sensitive to Co or verapamil. Under a voltage-clamp condition, membrane depolarization more positive than -20 mV evoked a Ca-dependent inward current, which was apparently prolonged and responsible for the generation of the long-lasting action potential. The appearance of the Ca action potential preceded that of a Na spike by about 24 h, and it developed so that the maximum rate of rise became 26 +/- 4 V/s by day 7. Then this Ca-dependent potential faded as the myotubes matured, until the action potentials became solely Na-dependent. The a.h.p. was evoked accompanying the Ca action potential and was inhibited by quinine or quinidine, showing that it is operated by Ca-activated K channels. This channel developed together with the Ca channel and continued to exist during the myotube maturation process. These results indicate that the MC3T3-A1/M13 myotube at the initial stage of development has a highly developed Ca spike system that is due mostly to a high-threshold-type Ca channel.
Amagai
Y
Y
Department of Physiology, Tohoku Dental University, Fukushima, Japan.
Kasai
S
S
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002460:Cell Line; D002999:Clone Cells / Q000378:metabolism / Q000502:physiology; D051379:Mice; D024510:Muscle Development; D009132:Muscles / Q000166:cytology / Q000378:metabolism / Q000502:physiology*
D015220:Calcium Channels; D002118:Calcium