Dynamic changes of intracellular calcium in osteoblast-like cells: effectson dye coupling

Toxic effects of metal ions released from enossal implant materials on bone cells may partly arise from toxic elevations of free intracellular calcium concentration ([Ca2+](i)). To analyzes such potential effects of elevated [Ca2+](i) on the coupling of bone cells mediated by Cx43 gap junctions, Fur a-2 loaded rat osteoblast-like (ROB) cells were stimulated by different pro cedures to undergo dynamic changes of [Ca2+](i). Ca2+ dynamics were correla ted with data of corresponding experiments in which the spread of Lucifer Y ellow had been investigated. After treatment with 0.5 mM ouabain (n = 137) [Ca2+](i) slowly increased from about 100 nM to less than or equal to 150 n M in 90 % of the cells, while in 10 % repetitive peak-like elevations to le ss than or equal to 500 nM occurred. The incidence of dye coupling decrease d from 94% (control) to 75%. Superfusion with sodium-free solution containi ng 0.5 mM ouabain (n = 290) elicited initial peak-like increases in [Ca2+]( i) to 500 nM in 41 % of the cells, whereas in 59 % of the cells [Ca2+](i) w as elevated to less than or equal to 170 nM. Concomitantly, dye coupling wa s reduced to 49 %. Application of 2 mu M A23187 (n = 345) gave rise to an i mmediate [Ca2+](i) peak ranging between 300 and 2000 nM followed by a susta ined [Ca2+](i) elevation in 99 % of the cells. The initial peak occurred al so in nominally Ca2+ free solution, demonstrating pronounced depletion of i ntracellular calcium stores, which was sufficient to uncouple greater than or equal to 90 % of the cells. Considering that elevated [Ca2+](i) is the p rimary parameter leading to uncoupling. a min ute-lasting elevation of [Ca2 +](i) to less than or equal to 500 nM was deduced from these experiments to be sufficient for uncoupling bone cells within their extended networks.