title: Potassium transport in nonpigmented epithelial cells of ocular ciliary body: inhibition of a Na+, K+, Cl- cotransporter by protein kinase C.
abstract: The mechanisms by which 86Rb+ (used as a tracer for K+) enters human nonpigmented ciliary epithelial cells were investigated. Ouabain-inhibitable bumetanide-insensitive 86Rb+ transport accounted for approximately 70-80% of total, whereas bumetanide-inhibitable ouabain-insensitive uptake accounted for 15-25% of total. K+ channel blockers such as BaCl2 reduced uptake by approximately 5%. Bumetanide inhibited 86Rb+ uptake with an IC50 of 0.5 microM, while furosemide inhibited with an IC50 of about 20 microM. Bumetanide-inhibitable 86Rb+ uptake was reduced in Na(+)-free or Cl(-)-free media, suggesting that Na+ and Cl- were required for optimal uptake via this mechanism. These characteristics are consistent with a Na+, K+, Cl- cotransporter in NPE cells. Treatment of NPE cells for 15 min with phorbol 12-myristate, 13-acetate (PMA), an activator of protein kinase C, caused a 50-70% decrease in 86Rb+ uptake via the Na+, K+, Cl- cotransporter. Other 86Rb+ uptake mechanisms were not affected. 86Rb+ uptake via the Na+, K+, Cl- cotransporter could be inhibited by other phorbol esters and by dioctanoylglycerol, an analog of diacylglycerol, but not by 4 alpha phorbol didecanoate, an ineffective activator of protein kinase C. Staurosporine, a protein kinase C inhibitor, blocked phorbol ester inhibition of 86Rb+ uptake. These data suggest that a Na+, K+, Cl- cotransporter in NPE cells is inhibited by activation of protein kinase C.
authors.affiliation: Department of Opthalmology, University of California, San Francisco 94143.
authors.forename: R B
authors.initials: RB
authors.lastname: Crook
authors.forename: D K
authors.initials: DK
authors.lastname: von Brauchitsch
authors.forename: J R
authors.initials: JR
authors.lastname: Polansky
mesh_terms: D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D002924:Ciliary Body / Q000378:metabolism*; D006801:Humans; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D015221:Potassium Channels; D028021:Sodium-Potassium-Chloride Symporters; D012964:Sodium; D011493:Protein Kinase C; D012413:Rubidium; D011188:Potassium