title: Pathways signaling the regulatory volume decrease of cultured nonpigmented ciliary epithelial cells.
abstract: OBJECTIVE
  The authors identify the signaling pathways for the regulatory volume decrease (RVD) of nonpigmented ciliary epithelial (NPE) cells. The RVD is a regulatory response triggered by swelling and reflecting KCl release by NPE cells.
  
  
  METHODS
  The cell volumes of human nonpigmented ciliary epithelial cells were measured in suspension by electronic cell sorting. Measurements were conducted in test solutions of constant ionic strength, but osmolality was varied by sucrose.
  
  
  RESULTS
  Cyclic AMP (cAMP), forskolin, PGE2, the PKC-inhibitor staurosporine, and increasing cytoplasmic Ca2+ activity with thapsigargin all enhanced the RVD. Leukotrienes A4, D4, E4, and the protein phosphatase inhibitor okadaic acid had no detectable effect under the current experimental conditions. The cyclooxygenase inhibitor indomethacin, the epoxygenase inhibitors ketoconazole and SKF 525A, and the PKC activator DiC8 all downregulated the RVD. The addition of the cation ionophore, gramicidin, increased the RVD. In the presence of gramicidin, cAMP, PGE2, and indomethacin did not affect the RVD, but ketoconazole, DiC8, and the calcium-calmodulin blocker trifluoroperazine still inhibited--and staurosporine still enhanced--the RVD. Many of these observations are strikingly different from results reported with other cells. Anisosmotic swelling did not increase intracellular cAMP concentration.
  
  
  CONCLUSIONS
  The pathways signaling the regulatory responses to swelling are unique for each cell type. The authors propose that hypotonic swelling of NPE cells stimulates arachidonic acid turnover, triggering PGE2-mediated upregulation of K+ channels and epoxide-mediated upregulation of Cl- channels. Swelling may also reduce endogenous PKC activity, further upregulating Cl- channels. Calcium-calmodulin plays a permissive role in upregulating the Cl- channels.
authors.affiliation: Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104-6085.
authors.forename: M M
authors.initials: MM
authors.lastname: Civan
authors.forename: M
authors.initials: M
authors.lastname: Coca-Prados
authors.forename: K
authors.initials: K
authors.lastname: Peterson-Yantorno
mesh_terms: D016718:Arachidonic Acid / Q000502:physiology; D002118:Calcium / Q000502:physiology; D002450:Cell Communication; D048429:Cell Size; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D018118:Chloride Channels / Q000502:physiology; D002924:Ciliary Body / Q000166:cytology / Q000502:physiology*; D006801:Humans; D010766:Phosphorylation; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013539:Simian virus 40
chemical_list: D018118:Chloride Channels; D016718:Arachidonic Acid; D002118:Calcium