Simultaneous changes of cell volume and cytosolic calcium concentration in macula densa cells caused by alterations of luminal NaCl concentration

Abstract

Cell volume and cytosolic Ca2+ concentration ([Ca2+]i) were measured in rabbit macula densa (MD) cells loaded with calcein and Fura Red using confocal microscopy. [Ca2+]i was also analysed with Indo-1 and fura-2. We used isolated microperfused thick ascending limbs with attached glomerulus. The results showed that when the luminal NaCl concentration ([NaCl]) was decreased from 35 to 10 mM, the cell volume decreased by 10.4%, and [Ca2+]i increased by 9.5%. This increase was inhibited in Ca2+-free solution. When luminal [NaCl] was changed from 35 to 135 mM, the cell volume increased by 15.1%, and [Ca2+]i did not change. The cell volume alterations were not different in Ca2+-free solutions. Using Indo-1, basal [Ca2+]i in MD cells was 107.8 nM. When luminal [NaCl] was changed from 135 to 10 mM, [Ca2]i increased by 23.5 nM. Using fura-2, the basal [Ca2+]i in MD cells was 115.3 nM, and when luminal [NaCl] was changed from 135 or 35 to 10 mM, [Ca2+]i change was 30.1 or 10.6 nM, respectively. An increase in [NaCl] caused no change in [Ca2+]i. In Ca2+-free solution, no change in [Ca2+]i occurred. A stepwise decrease in luminal [NaCl] resulted in a sigmoid increase in [Ca2+]i in MD cells. The steepest part of the curve was between 70 and 10 mM. In conclusion, we found that MD cells have cell volume regulation, and that [Ca2+]i elevation caused by decreased luminal [NaCl] is independent of the cell volume. © The Physiological Society 2005.