title: cAMP Stimulates Transepithelial Short-Circuit Current and Fluid Transport Across Porcine Ciliary Epithelium.
abstract: To investigate the effects of cAMP on transepithelial electrical parameters and fluid transport across porcine ciliary epithelium.
  
  
  
  Transepithelial electrical parameters were determined by mounting freshly isolated porcine ciliary epithelium in a modified Ussing chamber. Similarly, fluid movement across intact ciliary body was measured with a custom-made fluid flow chamber.
  
  
  
  Addition of 1, 10, and 100 μM 8-Br-cAMP (cAMP) to the aqueous side (nonpigmented ciliary epithelium, NPE) induced a sustained increase in short-circuit current (Isc). Addition of niflumic acid (NFA) to the aqueous surface effectively blocked the cAMP-induced Isc stimulation. The administration of cAMP to the stromal side (pigmented ciliary epithelium, PE) triggered a significant stimulation of Isc only at 100 μM. No additive effect was observed with bilateral application of cAMP. Likewise, forskolin caused a significant stimulation of Isc when applied to the aqueous side. Concomitantly, cAMP and forskolin increased fluid transport across porcine ciliary epithelium, and this stimulation was effectively inhibited by aqueous NFA. Depleting Cl- in the bathing solution abolished the baseline Isc and inhibited the subsequent stimulation by cAMP. Pretreatment with protein kinase A (PKA) blockers (H89/KT5720) significantly inhibited the cAMP- and forskolin-induced Isc responses.
  
  
  
  Our results suggest that cAMP triggers a sustained stimulation of Cl- and fluid transport across porcine ciliary epithelium; Cl- channels in the NPE cells are potentially a cellular site for this PKA-sensitive cAMP-mediated response.
authors.affiliation: Laboratory of Experimental Optometry, School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong.
authors.forename: Angela King-Wah
authors.initials: AK
authors.lastname: Cheng
authors.affiliation: Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States 3Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States 4Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States.
authors.forename: Mortimer M
authors.initials: MM
authors.lastname: Civan
authors.affiliation: Laboratory of Experimental Optometry, School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong.
authors.forename: Chi-Ho
authors.initials: CH
authors.lastname: To
authors.affiliation: Laboratory of Experimental Optometry, School of Optometry, The Hong Kong Polytechnic University, Hung Hom, Hong Kong.
authors.forename: Chi-Wai
authors.initials: CW
authors.lastname: Do
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D018118:Chloride Channels / Q000378:metabolism; D002924:Ciliary Body / Q000166:cytology / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism; D023421:Models, Animal; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism*; D013552:Swine
chemical_list: D018118:Chloride Channels; D000242:Cyclic AMP