Palmitate Stimulates the Epithelial Sodium Channel by Elevating Intracellular Calcium, Reactive Oxygen Species, and Phosphoinositide 3-Kinase Activity

Figure 3

Palmitate stimulates ENaC via a Ca²⁺-dependent mechanism. (a) Representative ENaC single-channel current recorded from an A6 cell before and after application of BAPTA-AM (a membrane-permeable Ca²⁺ chelator; 10 μM) and palmitate (0.3 mM) to the basolateral bath. (b) Summarized ENaC _O before and after the application of different reagents (; , compared with the control). (c) Representative single-channel ENaC current recorded from an A6 cell before and after application of 2-APB (an inhibitor of IP3 receptors which inhibits store-operated calcium release; 100 μM) and palmitate (0.3 mM) to the basolateral bath. (d) Summarized ENaC _O before and after application of different reagents (; , compared with the control). (e) Representative confocal microscopy images of A6 cells, which were loaded with Fluo-3, AM (a Ca²⁺ indicator), under control conditions (before), 5 min after treatment with 2-APB, and after application of palmitate to the basolateral bath. (f) Summary plots of fluorescence intensity of Fluo-3 indicating the levels of intracellular Ca²⁺. Each point was averaged from 8 images. Data are from six separate experiments. (g) Representative confocal microscopy images of A6 cells, which were loaded with Fluo-3, AM, before (in the absence of extracellular Ca²⁺) and after application of palmitate to the basolateral bath. (h) Summary plots of fluorescence intensity of Fluo-3 indicating the levels of intracellular Ca²⁺. Each point was averaged from 8 images. Data are from six separate experiments.

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