Calcium-induced calcium release participates in cell volume regulation of rabbit TALH cells

Abstract

Changes of cell volume and intracellular calcium concentration ([Ca(2+)](i)) in immortalized thick ascending limb of Henle's loop (TALH) cells were monitored using confocal laser scanning microscopy and fura-2 fluorescence, respectively. Reduction of the extracellular osmolarity from 600 to 300 mosmol/l induced cell swelling followed by regulatory volume decrease (RVD). Simultaneously, the [Ca(2+)](i) increased transiently. The calcium rise was not observed in calcium-free solution or in the presence of nifedipine, indicating that the change was, in the first place, due to the activation of a calcium influx. Application of ATP or caffeine in isotonic solutions increased transiently the [Ca(2+)](i) which revealed the existence of stores in TALH cells sensitive to inositol-1,4,5 trisphosphate (IP(3)) and ryanodine. To examine the possibility that the calcium influx might induce calcium release, manganese quenching experiments were performed. In hypotonic calcium-free solutions, the decay of the calcium-insensitive and calcium-sensitive fluorescence occurred simultaneously. In the presence of extracellular calcium however, the calcium-sensitive wavelength revealed initial calcium influx followed by a calcium release from intracellular stores. Thus, the calcium influx was a prerequisite for the calcium release. We conclude that calcium-induced calcium release participates in global calcium signalling during RVD of TALH cells.

TRPV4 exhibits a functional role in cell-volume regulation

“…This hypothetical regime is supported by the observation that neither HaCaT keratinocytes nor TRPV4-transfected CHO cells showed any signs of [Ca 2+ ] i increase or RVD in Ca 2+ -free solution. Furthermore, in TALH cells or human cervical cancer cells, Ca 2+ influx was also necessary for RVD (Shen et al, 2001;Tinel et al, 2002). While this paper was under revision, Arniges et al (Arniges et al, 2004) showed that downregulation of TRPV4 using antisense oligonucleotides abolished RVD and Ca 2+ entry in a volumeregulating tracheal epithelial cell line.…”

“…The ability to undergo RVD has been established for all three cell types (Tinel et al, 2002;Millar et al, 2004) (this report). Another volume-regulating cell type, HBE cells, has been shown to contain TRPV4 transcript as well (FernandezFernandez et al, 2002).…”

“…Following hypo-osmolarity-induced cell swelling, a rise in the cytosolic Ca 2+ concentration ([Ca 2+ ] i ) has been observed in different volume-regulating cell types, including human bronchial epithelial cells (HBEs), bovine articular chondrocytes (BACs) and TALH cells, and also in Trypanosoma cruzi during all three life-cycle stages (Fernandez-Fernandez et al, 2002;Rohloff et al, 2003;Tinel et al, 2002;Yellowly et al, 2002). Furthermore, RVD of TALH cells and human cervical-cancer cells was abolished in Ca 2+ -free medium (Shen et al, 2001;Tinel et al, 2002).…”

“…Furthermore, RVD of TALH cells and human cervical-cancer cells was abolished in Ca 2+ -free medium (Shen et al, 2001;Tinel et al, 2002). Two cation channels, TRPV2 and TRPV4, members of the vanilloid subfamily of transient-receptorpotential channels (TRP), might play a role in volume regulation.…”

Role of lipid rafts in membrane delivery of renal epithelial Na+-K+-ATPase, thick ascending limb

“…SV40-transformed rabbit TAL cells obtained from rabbit kidney medulla were cultured as described (37). We have selected these cells for their fine structure and polar organization criteria by electron microscopy analysis.…”