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unescu1,1 Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801; 2 Department of Biology, Indiana University-Purdue University at Indianapolis, Indianapolis 46202; and 3 Cardiovascular Research, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285
Blocker-induced noise analysis of epithelial Na+ channels (ENaCs) was used to investigate how inhibition of an LY-294002-sensitive phosphatidylinositol 3-kinase (PI 3-kinase) alters Na+ transport in unstimulated and aldosterone-prestimulated A6 epithelia. From baseline Na+ transport rates (INa) of 4.0 ± 0.1 (unstimulated) and 9.1 ± 0.9 µA/cm2 (aldosterone), 10 µM LY-294002 caused, following a relatively small initial increase of transport, a completely reversible inhibition of transport within 90 min to 33 ± 6% and 38 ± 2% of respective baseline values. Initial increases of transport could be attributed to increases of channel open probability (Po) within 5 min to 143 ± 17% (unstimulated) and 142 ± 10% of control (aldosterone) from baseline Po averaging near 0.5. Inhibition of transport was due to much slower decreases of functional channel densities (NT) to 28 ± 4% (unstimulated) and 35 ± 3% (aldosterone) of control at 90 min. LY-294002 (50 µM) caused larger but completely reversible increases of Po (215 ± 38% of control at 5 min) and more rapid but only slightly larger decreases of NT. Basolateral exposure to LY-294002 induced no detectable effect on transport, Po or NT. We conclude that an LY-294002-sensitive PI 3-kinase plays an important role in regulation of transport by modulating NT and Po of ENaCs, but only when presented to apical surfaces of the cells.
epithelial sodium channels; noise analysis; electrophysiology; kidney; cortical collecting ducts; A6 cell line
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