NA+ CA2+ EXCHANGER OVEREXPRESSION IMPAIRS CALCIUM SIGNALING IN FIBROBLASTS - INHIBITION OF THE [CA2(+)] INCREASE AT THE CELL PERIPHERY AND RETARDATION OF CELL-ADHESION/

We examined the Ca2+ handling property and cell function of CCL39 fibr oblasts highly overexpressing the cardiac isoform (NCX1) of Na+/Ca2+ e xchanger. In NCX1 transfectants in 146 mM Na+, ionomycin, alpha-thromb in or thapsigargin only produced a small transient increase in [Ca2+]( i) compared to the large increase seen in control cells, although rest ing [Ca2+](i) was not significantly different between these cells. In Na+-free medium, in contrast, the [Ca2+](i) responses in NCX1 transfec tants and control cells stimulated with these agents were not differen t, indicating that the Ca2+ content of the intracellular store(s) does not decrease on NCX1 transfection. The expression levels of the endo plasmic reticulum and plasma membrane Ca2+-ATPases, and thrombin- or s erum-stimulated cell growth were not altered in NCX1 transfectants, Th e latter finding suggests that Ca2+ signaling in the nucleus is not im paired appreciably On fluorescence imaging and confocal microscopy, we found that [Ca2+] did not increase in the peripheral cytoplasm of the se cells treated with a-thrombin in Na+-containing medium. In these NC X1 transfectants, activation of the plasma membrane Ca2+-activated Kchannels by thrombin or ionomycin was markedly suppressed, and the int egrin-mediated adhesion to substrate was significantly delayed compare d with control cells. NCX1-overexpressing CCL39 cells thus seem to be a good model with which we can study the Ca2+-regulated membrane proce sses under physiologically relevant conditions.