Physiological significance of hypotonicity-induced regulatory volume decrease: reduction in intracellular Cl- concentration acting as an intracellular signaling

Am J Physiol Renal Physiol. 2007 May;292(5):F1411-7. doi: 10.1152/ajprenal.00244.2006. Epub 2007 Jan 23.


Regulatory volume decrease (RVD) occurs after hypotonicity-caused cell swelling. RVD is caused by activation of ion channels and transporters, which cause effluxes of K(+), Cl(-), and H(2)O, leading to cell shrinkage. Recently, we showed that hypotonicity stimulated transepithelial Na(+) reabsorption via elevation of epithelial Na(+) channel (alpha-ENaC) expression in renal epithelia A6 cells in an RVD-dependent manner and that reduction of intracellular Cl(-) concentration ([Cl(-)](i)) stimulated the Na(+) reabsorption. These suggest that RVD would reveal its stimulatory action on the Na(+) reabsorption by reducing [Cl(-)](i). However, the reduction of [Cl(-)](i) during RVD has not been definitely analyzed due to technical difficulties involved in halide-sensitive fluorescent dyes. In the present study, we developed a new method for the measurement of [Cl(-)](i) change during RVD by using a high-resolution flow cytometer with a halide-specific fluorescent dye, N-(6-methoxyquinolyl) acetoethyl ester. The [Cl(-)](i) in A6 cells in an isotonic medium was 43.6 +/- 3.1 mM. After hypotonic shock (268 to 134 mosmol/kgH(2)O), a rapid increase of cell volume followed by RVD occurred. The RVD caused drastic diminution of [Cl(-)](i) from 43.6 to 10.8 mM. Under an RVD-blocked condition with NPPB (Cl(-) channel blocker) or quinine (K(+) channel blocker), we did not detect the reduction of [Cl(-)](i). Based on these observations, we conclude that one of the physiological significances of RVD is the reduction of [Cl(-)](i) and that RVD shows its action via reduction of [Cl(-)](i) acting as an intracellular signal regulating cellular physiological functions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Body Water / metabolism
  • Cell Line
  • Cell Size / drug effects*
  • Chloride Channels / antagonists & inhibitors
  • Chlorides / metabolism*
  • Flow Cytometry
  • Fluorescence
  • Fluorescent Dyes / pharmacokinetics
  • Hypertonic Solutions / pharmacology*
  • Intracellular Membranes / metabolism*
  • Kidney / cytology*
  • Kidney / drug effects
  • Kidney / metabolism*
  • Nitrobenzoates / pharmacology
  • Osmolar Concentration
  • Quinine / pharmacology
  • Quinolines / pharmacokinetics
  • Signal Transduction*
  • Xenopus laevis


  • Chloride Channels
  • Chlorides
  • Fluorescent Dyes
  • Hypertonic Solutions
  • Nitrobenzoates
  • Quinolines
  • N-(6-methoxyquinolyl)acetoethyl ester
  • 5-nitro-2-(3-phenylpropylamino)benzoic acid
  • Quinine