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Am J Physiol Renal Physiol (June 26, 2002). doi:10.1152/ajprenal.00011.2002
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Articles in PresS, published online ahead of print June 26, 2002
Am J Physiol Renal Physiol, 10.1152/ajprenal.00011.2002
Submitted on January 10, 2002
Accepted on June 3, 2002

Phosphatase Inhibitors Increase the Open Probability of ENaC in A6 Cells

A. Becchetti1, B. Malik1, G. Yue1, P. Duchatelle1, O. Al-Khalili1, T. R. Kleyman2, and D. C. Eaton1*

1 Department of Physiology, Emory University School of Medicine, Atlanta, GA, USA
2 Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA

* To whom correspondence should be addressed. E-mail: deaton{at}emory.edu.

We studied cellular phosphatase inhibitors, okadaic acid (OKA), calyculin A, and microcystin, on ENaC in A6 renal cells. OKA increased amiloride-sensitive current after about 30 minutes with maximal stimulation at 1 - 2 hours. Fluctuation analysis of cell-attached patches containing a large number of ENaC yielded power spectra with corner frequencies in untreated cells almost twice as large as in cells pretreated for 30 minutes with OKA implying an increase in single channel open probability (Po) that doubled after okadaic acid. Single channel analysis showed that in cells pretreated with okadaic acid, Po and mean open time approximately doubled. Two other phosphatase inhibitors, calyculin A and microcystin, had similar effects on open probability and mean open time. An analog of okadaic acid, okadaone, which does not inhibit phosphatases had no effect. Pretreatment with 10 nM OKA, which blocks PP2A but not PP1 in mammalian cells, had no effect even though both phosphatases are present in A6 cells. Many proteins were differentially phosphorylated after OKA, but ENaC subunit phosphorylation did not increase. We conclude that, in A6 cells, there is an OKA-sensitive phosphatase which suppresses ENaC activity by altering the phosphorylation of a regulatory molecule associated with the channel.




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