PROCEEDINGS |
Cytosolic calcium concentration [Ca] plays a vital role in cell signaling. With the use of fluorescent probes, such as fura 2, and fluorescence microscopy it is now routinely possible to accurately measure changes in [Ca]. However, complications and technical issues should be carefully considered in certain applications. Work in our laboratory has used single cell photometry, conventional image analysis, and confocal microscopy to measure [Ca] in renal cells. Most of our work has focused on macula densa cells which detect changes in distal tubular fluid sodium chloride concentration and transmit signals to the glomerular vasculature. In recent studies, we have found that increases in luminal [NaCl] from a normal low value of 25 mM to 150 mM result in increases in macula densa [Ca]. This increase in [Ca] occurs not through calcium mobilization but through calcium entry across the basolateral membrane. Increases in macula densa [Ca] can be blocked by nifedipine, a voltage operated calcium channel blocker. Thus, the use of fluorescence microsopy has allowed us to establish the existence of a macula densa [Ca] signaling pathway.