Measurement of intracellular Ca2+ in BC3H-1 muscle cells with Fura-2: relationship to acetylcholine receptor synthesis |
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Authors: | J R Berlin M A Wozniak M B Cannell R J Bloch W J Lederer |
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Institution: | Department of Physiology, School of Medicine, University of Maryland, Baltimore. |
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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. |
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