Potassium transport in nonpigmented epithelial cells of ocular ciliary body: Inhibition of a Na+, K+, Cl− cotransporter by protein kinase C
✍ Scribed by Richard B. Crook; Douglas K. Von Brauchitsch; Jon R. Polansky
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 724 KB
- Volume
- 153
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
The mechanism by which ^86^Rb^+^ (used as a tracer for K^+^) enters human nonpigmented ciliary epithelial cells were investigated. Ouabain‐inhibitable bumetanide‐insensitive ^86^Rb^+^ transport accounted for ∼70–80% of total, whereas bumetanide‐inhibitable ouabain‐insensitive uptake accounted for 15–25% of total. K^+^ channel blockers such as BaCl~2~ reduced uptake by ∼5%. Bumetanide inhibited ^86^Rb^+^ uptake with an IC~50~ of 0.5 μM, while furosemide inhibited with an IC~50~ of about 20 μM. Bumetanide‐inhibitable ^86^Rb^+^ 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^−^ contransporter 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 ^86^Rb^+^ uptake via the Na^+^, K^+^, Cl^−^ cotransporter. Other ^86^Rb^+^ uptake mechanisms were not affected. ^86^Rb^+^ uptake via the Na^+^, K^+^, Cl^−^ contransporter could be inhibited by other phorbol esters and by dioctanoylglycerol, an analog of diacylglycerol, but not by 4α phorbol didecanoate, an ineffective activator of protein kinase C. Staurosporine, a protein kinase C inhibitor, blocked phorbol ester inhibition of ^86^Rb^+^ uptake. These data suggest that a Na^+^, K^+^, Cl^−^ cotransporter in NPE cells is inhibited by activation of protein kinase C. © 1992 Wiley‐Liss, Inc.