TRPV4 exhibits a functional role in cell-volume regulation.
Tight regulation of the cell volume is important for the maintenance of cellular homeostasis. In a hypotonic environment, cells swell owing to osmosis. With many vertebrate cells, swelling is followed by an active reduction of volume, a process called regulatory volume decrease (RVD). A possible participant in RVD is the non-selective cation channel TRPV4, a member of the TRP superfamily that has been shown to react to hypotonic stimuli with a conductance for Ca2+. As a model for cell-volume regulation, we used a human keratinocyte cell line (HaCaT) that produces TRPV4 endogenously. When HaCaT cells were exposed to a hypotonic solution (200 mOsm) maximal swelling was followed by RVD. During swelling and volume regulation, a strong Ca2+ influx was measured. Gd3+, an inhibitor of TRPV4, blocked RVD of HaCaT cells and the accompanying rise of cytosolic Ca2+. To define the role of TRPV4 in volume regulation, a TRPV4-EGFP fusion protein was produced in CHO cells. CHO cells are unable to undergo RVD under hypotonic conditions and do not produce TRPV4 endogenously. Fluorescence imaging revealed that recombinant TRPV4 was localized to the cell membrane. Production of TRPV4 enabled CHO cells to undergo typical RVD after hypo-osmolarity-induced cell swelling. RVD of TRPV4-transfected CHO cells was significantly reduced by Gd3+ treatment or in Ca2+-free solution. Taken together, these results show a direct participation of TRPV4 in RVD.
Becker
Daniel
D
Kinematic Cell Research Group, Johann Wolfgang Goethe University, Marie-Curie-Str. 9, 60439 Frankfurt, Germany.
Blase
Christopher
C
Bereiter-Hahn
Juergen
J
Jendrach
Marina
M
D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D048429:Cell Size / Q000187:drug effects; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D005682:Gadolinium / Q000494:pharmacology; D015870:Gene Expression; D006801:Humans; D007038:Hypotonic Solutions; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009995:Osmosis; D050916:TRPV Cation Channels
D027682:Cation Transport Proteins; D007038:Hypotonic Solutions; D007473:Ion Channels; D050916:TRPV Cation Channels; C416986:TRPV4 protein, human; D005682:Gadolinium; D002118:Calcium