THE NITRIC-OXIDE DONOR, SODIUM-NITROPRUSSIDE, INCREASED INTRANUCLEAR AND CYTOSOLIC-FREE CALCIUM-CONCENTRATION IN SINGLE PU5-1.8 CELLS

In the present study, the effect of sodium nitroprusside (SNP), a nitric oxide (NO) releasing agent, on the intracelluar free calcium concentration ([Ca2+]i) was studied. Our results demonstrate that SNP could increase [Ca2+]i in single PU5-1.8 cells, a murine macrophage cell line, as determined by confocal laser scanning microscope with calcium green-1 fluorescent probe. In the presence of hemoglobin, a NO scavenger, the effect of SNP on the Ca2+ level was suppressed. Our data also show that the intranuclear Ca2+ ([Ca2+]n) was always higher than those in cytosol. Stimulation of cells with 1mM SNP induced an immediate increase of [Ca2+]n with a delayed rise of cytosolic Ca2+ ([Ca2+]c). Interestingly, when cells were subsequently treated with 2mM SNP, an increase of [Ca2+]c with a similar pattern to the rise [Ca2+]n was observed. In Ca2+-free buffer, SNP also raised the [Ca2+]n and [Ca2+]c. When Ca2+ was added to the buffer, a second peak of [Ca2+]n and several spikes of [Ca2+]c were observed. These results thus indicate that 1) NO may increase both [Ca2+]n and [Ca2+]c in PU5-1.8 cells; 2) the increase of [Ca2+]n requires both internal and external Ca2+. Moreover, the diverse responses in these cells suggest that the regulation of Ca2+ in these areas may be different. (C) 1994 Academic Press, Inc.