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Calcium release activated membrane channels of osteoblast‐like cells: targets and entrance gates for metal cations?
Author(s) -
Wiemann M.,
Bingmann D.
Publication year - 1999
Publication title -
materialwissenschaft und werkstofftechnik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.285
H-Index - 38
eISSN - 1521-4052
pISSN - 0933-5137
DOI - 10.1002/(sici)1521-4052(199912)30:12<755::aid-mawe755>3.0.co;2-3
Subject(s) - chemistry , thapsigargin , calcium , extracellular , biophysics , flufenamic acid , intracellular , osteoblast , fura 2 , cytosol , biochemistry , in vitro , biology , organic chemistry , enzyme
Enossal metal implants release ions which alter e. g. the Ca 2+ ‐based signaling of bone cells. One crucial element of this Ca 2+ signaling is the calcium release activated calcium flux (CRAC) which is involved in the refilling of the cell's intracellular Ca 2+ stores (ICS). Properties of this CRAC were studied in cultured osteoblast‐like (OBL) cells using the Ca 2+ sensitive fluorescent dye fura‐2. CRAC channels were opened by depleting ICS in the absence of extracellular calcium ([Ca 2+ ] e ) by either thapsigargin (5 μM) or 4‐bromo‐A23187 (2 μM). Elevation of [Ca 2+ ] e to 1.8 mM then increased the free intracellular Ca 2+ ([Ca 2+ ] i ). This Ca 2+ influx was a typical CRAC and could be blocked by flufenamic acid (100 μM) which is a characteristic inhibitor of cation channels with low selectivity. Induction of CRAC enhanced the influx of extracellular Mn 2+ (2 mM) 4.3fold, as measured by quenching of flura‐2 fluorescence. Ni 2+ , on the one hand, potentiated the immediate CRAC while, on the other hand, it reversibly inhibited Ca 2+ influx at a later stage. Similarly, Pb 2+ (> 5 μM) dose dependently inhibited the immediate CRAC. Using the high affinity of fura‐2 to Pb 2+ and the resulting Ca 2+ binding‐like change of the optical signal, the permeation of Pb 2+ into OBL cells could be detected. This binding could be reversed by the cell permeant heavy metal chelator N,N,N′,N′‐tetrakis(2‐pyridylmethyl)‐ethylenediamine (TPEN). At the single cell level, the permeation of Pb 2+ correlated with increasing amounts of CRAC. Even low concentrations of Pb 2+ (1 μM), which have been found in the blood of human individuals, clearly increased the fura‐2 signal. These results highlight CRAC channels of OBL cells as a possible entrance gate and / or a target for metal ions which may be released from metal implant materials.