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Dependence of cytosolic calcium in differentiating rat pheochromocytoma cells on calcium channels and intracellular stores.
Author(s) -
Reber B F,
Reuter H
Publication year - 1991
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1991.sp018502
Subject(s) - calcium , cytosol , intracellular , calcium in biology , chemistry , microbiology and biotechnology , pheochromocytoma , biophysics , t type calcium channel , voltage dependent calcium channel , endocrinology , biology , biochemistry , enzyme , organic chemistry
1. The rat clonal pheochromocytoma cell line (PC12) was used to study changes in the free intracellular Ca2+ concentration [( Ca2+]i) that are related to the distribution of L‐type (dihydropyridine‐sensitive) and N‐type (omega‐conotoxin‐sensitive) calcium channels during nerve growth factor (NGF)‐induced outgrowth of neurites. Changes in [Ca2+]i during K+ depolarization were recorded by means of Fura‐2 single‐cell microfluorimetry. 2. The basal [Ca2+]i of cells at rest was not altered by long‐term treatment with NGF, neither in the cell bodies nor in the growth cones. K+ depolarization of the cells caused a rise in [Ca2+]i. 3. The dihydropyridine (DHP) nifedipine alone, or together with omega‐conotoxin (omega‐CgTX), were similarly effective in inhibiting the K(+)‐induced increase in [Ca2+]i in untreated and NGF‐treated cell bodies, arguing for a preferential distribution of L‐type Ca2+ channels in this cell area. By contrast, after 6‐7 days exposure to NGF the K(+)‐induced initial transient rise of [Ca2+]i in growth cones was very sensitive to omega‐CgTX, whereas nifedipine affected only the sustained rise. 4. PC12 cells also contain caffeine‐ and inositol trisphosphate (IP3)‐sensitive intracellular Ca2+ stores. Addition of 30 mM‐caffeine caused a fast transient rise in [Ca2+]i. The extent of filling of the caffeine‐sensitive pool affected basal [Ca2+]i. These Ca2+ storage sites were empty under normal culture conditions. However, a single K+ depolarization caused filling of the stores, followed by spontaneous depletion (50% in about 5 min) after wash‐out of high [K+]o. When the caffeine‐sensitive stores were empty, the rise in [Ca2+]i was attenuated during submaximal depolarization. Caffeine‐sensitive Ca2+ stores were also present in some growth cones, though with much smaller capacities than in cell bodies. 5. Mobilization of Ca2+ from the IP3‐sensitive store, by bradykinin exposure, was found to be independent of the caffeine‐sensitive pool. There was no apparent ‘cross‐talk’ between both Ca2+ pools. 6. We conclude that changes in [Ca2+]i in cell bodies depend on both membrane Ca2+ channels and intracellular Ca2+ stores. During NGF‐induced differentiation there is a predominance of N‐type Ca2+ channels in growth cones, while Ca2+ stores are of minor importance in these structures.