Effect of various agents on the cytoplasmic calcium concentration in cultured human muscle cells.
1. We determined the cytoplasmic Ca2+ concentration ([Ca2+]i) in cultured human muscle cells using the fluorescent indicator Quin-2. 2. The [Ca2+]i was dependent on the external Ca2+ concentration. Acetylcholine in the presence of external Ca2+ caused a transient increase in [Ca2+]i. Inhibition by nifedipine indicated that this response was mediated through activated voltage-operated channels. In nominally Ca2(+)-free buffer acetylcholine did not markedly increase [Ca2+]i. Therefore, the increase in [Ca2+]i as a response to depolarization is mainly due to influx of external Ca2+. 3. Various concentrations of caffeine did not influence the [Ca2+]i. Dantrolene decreased [Ca2+]i, both in the presence and absence of external Ca2+. The reduction probably resulted from an action of dantrolene on the intracellular Ca2+ stores, since dantrolene did not influence 45Ca2+ influx or efflux and caffeine partially counteracted the reduction.
Jacobs
A E
AE
Department of Biochemistry, University of Nijmegen, The Netherlands.
Benders
A A
AA
Oosterhof
A
A
Veerkamp
J H
JH
Wevers
R A
RA
Joosten
E G
EG
D000109:Acetylcholine / Q000494:pharmacology; D000293:Adolescent; D000328:Adult; D000634:Aminoquinolines; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D003620:Dantrolene / Q000494:pharmacology; D004553:Electric Conductivity; D005456:Fluorescent Dyes; D006801:Humans; D008875:Middle Aged; D009132:Muscles / Q000166:cytology / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology
D000634:Aminoquinolines; D005456:Fluorescent Dyes; D002110:Caffeine; D003620:Dantrolene; D009543:Nifedipine; D000109:Acetylcholine; C035739:Quin2; D002118:Calcium