Elevated potassium ion in lacrimal fluid and the health of the ocular surface

Summary

Principal Investigator: John Ubels
Abstract: DESCRIPTION (provided by applicant): The tears differ from most extracellular fluids in that the K+ concentration of tears is about 20 mEq/l. It is thought that the ducts of the lacrimal gland secrete K+;however, the mechanism of this secretion has not been fully elucidated, and the purpose of the high [K+] in tears with respect to its relationship to the cells of the ocular surface is unknown. The key hypotheses to be addressed are based on these observations: 1) Lacrimal gland ducts express K+ transporters and channels consistent with secretion of K+ by the ducts, 2) UV radiation causes opening of K+ channels and loss of K+ from corneal epithelial cells and this loss of K+ activates apoptotic pathways. 3) Elevating extracellular K+ ([K+]o) prevents activation of apoptotic pathways in lymphocytes. We propose that the lacrimal gland duct cells secrete fluid high in K+, which provides the ocular surface with an extracellular ionic environment that protects these cells from the deleterious effects of ambient levels of ultraviolet (UV) radiation. The relatively high level of K+ in tears prevents the loss of intracellular K+ and the activation of apoptotic mechanisms when ocular surface cells are exposed to UV radiation. The specific aims of the proposed research are, 1) to determine, using patch clamp recording, whether K+ and Cl- channels, previously identified in lacrimal duct cells by microarrays and confocal microscopy are active in these cells. 2) To determine the role of elevated [K+] in tears, corneal epithelial cells will be exposed to UV radiation in the presence of varying [K+]o followed by measurement of cell viability, activation of apoptotic pathways and activity of ion channels, 3) To determine whether elevating [K+] in culture medium will promote the proliferation and viability corneal epithelial cells in culture. This study of the role of high potassium in tears will elucidate the relationship of the tears to the health of the eye in normal individuals and dry-eye patients. Everyone is exposed to ambient UV radiation and the proposed research will help to explain how the cornea protects the lens and retina from UV radiation while suffering minimal damage. In dry eye disease an inadequate tear film may make the cornea more susceptible to damage by UV radiation, thereby contributing to the disease process. If the high potassium in tears is important for the health of the ocular surface, this information will be useful in the development of improved treatments for dry eye disease.
Funding Period: 2007-06-01 - 2010-05-31
more information: NIH RePORT

Top Publications

  1. pmc Enhancement of vitamin D metabolites in the eye following vitamin D3 supplementation and UV-B irradiation
    Yanping Lin
    Department of Entomology and Cancer Center, University of California, Davis, CA, USA
    Curr Eye Res 37:871-8. 2012
  2. pmc Potassium ion fluxes in corneal epithelial cells exposed to UVB
    John L Ubels
    Department of Biology, Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA
    Exp Eye Res 92:425-31. 2011
  3. pmc Stratified corneal limbal epithelial cells are protected from UVB-induced apoptosis by elevated extracellular K⁺
    Mark P Schotanus
    Department of Biology, Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA
    Exp Eye Res 93:735-40. 2011
  4. ncbi Elevated extracellular K+ inhibits apoptosis of corneal epithelial cells exposed to UV-B radiation
    Katherine R Singleton
    Department of Biology, Calvin College, Grand Rapids, MI 49546, USA
    Exp Eye Res 89:140-51. 2009
  5. pmc Inhibition of UV-B induced apoptosis in corneal epithelial cells by potassium channel modulators
    John L Ubels
    Department of Biology, Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA
    Exp Eye Res 90:216-22. 2010

Scientific Experts

  • John Ubels
  • Mark P Schotanus
  • Yanping Lin
  • Leah R Koetje
  • Katherine R Singleton
  • Mitchell A Watsky
  • Zhaohong Yin
  • Victorina Pintea
  • Bruce D Hammock
  • Rachel E Van Dyken
  • Loren D Haarsma
  • David S Will
  • Susan L Bardolph

Detail Information

Publications5

  1. pmc Enhancement of vitamin D metabolites in the eye following vitamin D3 supplementation and UV-B irradiation
    Yanping Lin
    Department of Entomology and Cancer Center, University of California, Davis, CA, USA
    Curr Eye Res 37:871-8. 2012
    ..We also determined if the corneal epithelium can synthesize vitamin D following UV-B exposure...
  2. pmc Potassium ion fluxes in corneal epithelial cells exposed to UVB
    John L Ubels
    Department of Biology, Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA
    Exp Eye Res 92:425-31. 2011
    ..The prevention of UVB-induced K(i)(+) loss by 25 mM K(o)(+) is consistent with the possible contribution of the relatively high K(+) concentration in tears to protection of the corneal epithelium from ambient UVB...
  3. pmc Stratified corneal limbal epithelial cells are protected from UVB-induced apoptosis by elevated extracellular K⁺
    Mark P Schotanus
    Department of Biology, Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA
    Exp Eye Res 93:735-40. 2011
    ..Based on these observations it is suggested that the relatively high K(+) concentration in tears (20-25 mM) may play a role in protecting the corneal epithelium from ambient UVB radiation...
  4. ncbi Elevated extracellular K+ inhibits apoptosis of corneal epithelial cells exposed to UV-B radiation
    Katherine R Singleton
    Department of Biology, Calvin College, Grand Rapids, MI 49546, USA
    Exp Eye Res 89:140-51. 2009
    ..This suggests that the relatively high [K(+)] in tears reduces loss of K(+) from corneal epithelial cells in response to UV exposure, thereby contributing to the protection of the ocular surface from ambient UV radiation...
  5. pmc Inhibition of UV-B induced apoptosis in corneal epithelial cells by potassium channel modulators
    John L Ubels
    Department of Biology, Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA
    Exp Eye Res 90:216-22. 2010
    ..This suggests the elevated [K(+)] in tears may protect the corneal epithelium from effects of ambient UV-B...