title: Measurement of intracellular Ca2+ in BC3H-1 muscle cells with Fura-2: relationship to acetylcholine receptor synthesis.
abstract: Synthesis of acetylcholine receptors (AChR) can be affected by calcium, but the role played by this cation is controversial. The effect of changes in extracellular calcium, [Ca2+]o, on AChR synthesis was examined in a cultured mouse muscle cell line, BC3H-1. Reduction of [Ca2+]o for long periods (approximately 22 h) leads to a decrease in total surface AChR levels, a finding that is consistent with inhibition of AChR synthesis. A half-maximal reduction in surface AChR levels is observed when [Ca2+]o is decreased from 1.8 to approximately 5o microM. Under these conditions, however, total protein synthesis is also largely inhibited, suggesting that the effect of [Ca2+]o on AChR synthesis may be relatively non-specific. Increasing [Ca2+]i by adding the Ca2+ ionophore, A23187 (in the presence of 1.8 mM [Ca2+]o) also gives similar and significant reductions of both AChR and protein synthesis. Since the time course of changes in intracellular calcium [( Ca2+]i) produced by these manoeuvres is unknown, we examined the effects of briefer (1-6 h) reductions in [Ca2+]o and achieved a more specific reduction in AChR synthesis. A direct measurement of the changes in [Ca2+]i resulting from changes in [Ca2+]o was made using the fluorescent indicator Fura-2 and video fluorescence microscopy. Our results show that in BC3H-1 muscle cells the resting intracellular calcium decreases reversibly over 20 min when [Ca2+]o is decreased. We suggest that a reduction of [Ca2+]i produced by the lower [Ca2+]o underlies the reduction in AChR synthesis observed in these experiments.
authors.affiliation: Department of Physiology, School of Medicine, University of Maryland, Baltimore.
authors.forename: J R
authors.initials: JR
authors.lastname: Berlin
authors.forename: M A
authors.initials: MA
authors.lastname: Wozniak
authors.forename: M B
authors.initials: MB
authors.lastname: Cannell
authors.forename: R J
authors.initials: RJ
authors.lastname: Bloch
authors.forename: W J
authors.initials: WJ
authors.lastname: Lederer
mesh_terms: D000818:Animals; D001572:Benzofurans / Q000008:administration & dosage; D002118:Calcium / Q000032:analysis* / Q000502:physiology; D002460:Cell Line; D016257:Fura-2; D007424:Intracellular Fluid / Q000032:analysis; D051379:Mice; D008845:Microinjections; D008856:Microscopy, Fluorescence / Q000379:methods; D009132:Muscles / Q000032:analysis / Q000166:cytology* / Q000648:ultrastructure; D011950:Receptors, Cholinergic / Q000378:metabolism
chemical_list: D001572:Benzofurans; D011950:Receptors, Cholinergic; D002118:Calcium; D016257:Fura-2