Calcium release induced by high K+ and caffeine in cultured skeletal muscle cells of embryonic chicken.
To further understand the function of excitation-contraction coupling in skeletal muscle cells developing in vitro, Ca2+ transients elicited by high-K+ depolarization in the presence and absence of extracellular Ca2+ were compared with Ca2+ release induced by caffeine in cultured skeletal muscle cells isolated from 9-day-old chicken embryos (E9). Almost all myoblasts and myotubes cultured for 1 (E9I1) to 8 (E9I8) days responded to 80 mM [K+]O with an elevation of [Ca2+]i. Although all myotubes cultured for more than 4 days exhibited Ca2+ release independent of extracellular Ca2+, only about 50% of E9I1 and E9I2 cells maintained their response to Ca(2+)-free high-[K+]O solution. Strikingly, a considerable proportion of cells of short-term culture were insensitive to 10 mM caffeine. Moreover, 46.8% of the caffeine-insensitive E9I1 and E9I2 cells, 29 out of 62, was still responsive to 80 mM [K+]O in the absence of extracellular Ca2+. Western blot and immunocytochemistry showed that ryanodine receptor (RyRs) expression increases with culture. The Ca2+ release from caffeine-insensitive cells induced by Ca(2+)-free high-[K+]O solution could be blocked by 100-200 microM ryanodine, which suggests the involvement of RyRs. Evidence is presented to show that a low resting [Ca2+]i may be one factor responsible for the caffeine insensitivity of RyRs in cells of short-term culture.
Zhang
X H
XH
Unit of Cell Signal Transduction, Shanghai Institute of Physiology, Chinese Academy of Sciences, China.
Wu
J
J
Shen
M X
MX
Zhu
P H
PH
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D004594:Electrophysiology; D007425:Intracellular Membranes / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology*
D015220:Calcium Channels; D002110:Caffeine; D011188:Potassium; D002118:Calcium