Regulation of cytosolic Ca2+ in clonal human muscle cell cultures.
Human muscle cells were grown in culture and clonally selected for fusion potential. The concentration of cytoplasmic ionized calcium, [Ca2+]i, was measured in monolayers of fused myotubes using the Ca2+ indicator indo-1. The contributions of independent routes of Ca2+ influx and efflux to/from the cytoplasm on [Ca2+]i were investigated. The resting [Ca2+]i was 170-190 nM in different cell clones. Acetylcholine increased [Ca2+]i by about 2-fold in the presence of absence of extracellular Ca2+. Cell depolarization by K+ elevated [Ca2+]i about 3-fold, and this increase was largely dependent on extracellular Ca2+. Replacing Na+ by N-methylglucammonium+ raised [Ca2+]i greater than 5-fold, and 50% of this increase was dependent on extracellular Ca2+. All these increases in [Ca2+]i were transient, returning to basal [Ca2+]i within 2 min. It is concluded that cells in culture [Ca2+]i can be elevated transiently by acetylcholine through Ca2+ release from intracellular stores, and by K through Ca2+ influx. The return to basal [Ca2+]i is due to Na+/Ca2+ exchange and Ca2+-ATPase activity.
Sarabia
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Division of Cell Biology, Hospital for Sick Children, Toronto, Ont., Canada.
Klip
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A
D000109:Acetylcholine / Q000494:pharmacology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002478:Cells, Cultured; D002999:Clone Cells / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D006801:Humans; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009136:Muscular Dystrophies / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism
D012964:Sodium; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium