On the Role of Calcium in the Regulatory Volume Decrease (RVD) Response in Ehrlich Mouse Ascites Tumor Cells

Abstract

The putative role for Ca2+ entry and Ca2+ mobilization in the activation of the regulatory volume decrease (RVD) response has been assessed in Ehrlich cells. Following hypotonic exposure (50% osmolarity) there is: (i) no increase in cellular Ins(1,4,5)P3 content, as measured in extracts from [2-3H]myoinositol-labeled cells, a finding at variance with earlier reports from our group; (ii) no evidence of Ca2+-signaling recorded in a suspension of fura-2-loaded cells; (iii) Ca2+-signaling in only about 6% of the single, fura-2-loaded cells at 1-mm Ca2+ (1% only at 0.1-mM Ca2+ and in Ca2+-free medium), as monitored by fluorescence-ratio imaging; (iv) no effect of removing external Ca2+ upon the volume-induced K+ loss; (v) no significant inhibition of the RVD response in cells loaded with the Ca2+ chelator BAPTA when the BAPTA-loading is performed in K+ equilibrium medium; (vi) an inhibition of the swelling-induced K+ loss (about 50%) at 1-mM Ba2+, but almost no effect of charybdotoxin (100 nm) or of clotrimazole (10 microM), reported inhibitors of the K+ loss induced by Ca2+-mobilizing agonists. Thus, Ca2+signaling by Ca2+ release or Ca2+ entry appears to play no role in the activation mechanism for the RVD response in Ehrlich cells.

Metabolic and ionic responses of trout hepatocytes to anisosmotic exposure

“…In hyposmotic medium, these [Ca 2+ ]i responses were not reflected in dramatic changes of the mean [Ca 2+ ]i levels but were clearly visible at the individual cell level. The reason underlying the heterogeneity of cellular responses is not clear, but a remarkable variability at the cell level has also been reported for other cells (Jorgensen et al, 1997). As in this previous study, the alterations of [Ca 2+ ]i did not seem to be closely related to the changes of cell volume in the trout hepatocytes.…”

Modulation of the Two-pore Domain Acid-sensitive K+ Channel TASK-2 (KCNK5) by Changes in Cell Volume

“…In both cell types it was demonstrated that RVD proceeds without increase, or even during a decrease, in [Ca 2ϩ ] i . RVD was not affected by maneuvers preventing Ca 2ϩ influx or its intracellular release (9,37). Cell swelling-and membrane stretch-activated K ϩ channels have been reported in gall bladder epithelium (38).…”

Cell swelling increases intracellular calcium in Necturuserythrocytes

“…As described by others (Jorgensen et al, 1997;Wang et al, 1996), a percent volume recovery at X minutes after hypotonic exposure was calculated as [(Vmax-VX min)/(Vmax-V0)]×100, where Vmax is the peak relative cell volume, V0 is the initial relative volume (or one) and VX min is the relative cell volume measured X minutes after hypotonic exposure. A percent volume decrease was calculated as [(percent recoveryexperimental)/ (percent recoverycontrol)]×100, where maximal recovery in hypotonic Ringer is 100%.…”