Role of calcium in the regulation of acetylcholine receptor synthese in cultured muscle cells*.
Embroyonic muscles differentiated in vitro were used to study the effects of intracellular Ca2+ ([Ca2+1]i) variations on the amount of acetylcholine receptors ([AChR]) in the cell membrane. 2. Increased Ca2+ concentration in the growth medium ([Ca2+]o) caused a marked elevation of AChR levels, apparently through de novo synthesis. 3. Agents known to increase [Ca2+]i and its accumulation in the sarcoplasmic reticulum (SR), such as ionophore A23187, sodium dantrolene (DaNa), or high [Mg2+]o all enhanced alpha-bungarotoxin (alpha-BGT) binding after 48 h of treatment. 4. Electrical stimulation or caffeine, both affectors of SR calcium release, brought about a decrease in [AChR] probably by suppressing its synthesis. 5. The effects of simultaneous treatment with two AChR-inducing agents, namely, high [Ca2+]o in the presence of tetrodotoxin (TTX) or high [Mg2+]o were not additive, thus suggesting action via a common saturable mediator. 6. Intermediate AChR levels obtained following simultaneous treatments with opposing effects, e.g., electrical stimulation in the presence of high [Ca2+]o or DaNa, suggest contradictory actions on a common mediator. 7. All these observations indicate a strong correlation between SR calcium levels and [AChR] on myotubes; while calcium accumulation in the Sr was followed by increased AChR synthesis, calcium release was accompanied by suppression of receptor synthesis.
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002038:Bungarotoxins / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D002642:Chick Embryo; D004558:Electric Stimulation; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000096:biosynthesis*; D012519:Sarcoplasmic Reticulum / Q000502:physiology
D002038:Bungarotoxins; D011950:Receptors, Cholinergic; D000109:Acetylcholine; D002118:Calcium