Endocardial TRPC-6 Channels Act as Atrial Mechanosensors and Load-Dependent Modulators of Endocardial/Myocardial Cross-Talk
Vesna Nikolova-Krstevski, Soeren Wagner, Ze Yan Yu, Charles D. Cox, Jasmina Cvetkovska, Adam P. Hill, Inken G. Huttner, Victoria Benson, Andreas A. Werdich, Calum MacRae, Michael P. Feneley, Oliver Friedrich, Boris Martinac and Diane Fatkin
Effects of Chronic (24 h) Cyclic Stretch on [Ca2+]i in AE Cells
(A) Control (top panel) and stretched (bottom panel) AE cells were stained with Fluo-4 following administration of hyperforin to activate TRPC-6. In control cells, strong and continuous Ca2+ influx through the evenly distributed TRPC-6 channels at the cell surface is indicated (white arrows, top panel inset). In chronically stretched cells, Ca2+ influx at the cell membrane is restricted to small, localized areas that form a green punctate pattern (white arrows, bottom panel inset). (B) Bar graph showing the effects of chronic stretch, hyperforin, and 1-oleoyl-2-acetyl-sn-glycerol (OAG), a mechanosensitive channel activator, on the [Ca2+]i (respective cell numbers = 26, 30, 32, 25, 33, 40, in the order shown in graph). Ca2+ uptake by TRPC-6 and mechanosensitive Ca2+ channels, in general, is lower in the 24-h stretched AE cells compared with the non-stretched (control) cells. (C) Representative TRPC-6 immunoblot of biotin-labeled/streptavidin-immunoprecipitated cell membrane fraction (M) and total cell lysate (T) from 0-, 1-, and 24-h stretched AE cells, showing depleted levels of TRPC-6 in the cell membrane fraction of the 24-h stretched cells. Bar graph shows quantification of TRPC-6 levels from 3 separate experiments. β-tubulin immunolabeling was used as loading control. See Supplemental Figure 7C for full Western blots. All values are mean ± SEM. *p < 0.001 versus control cells. See Supplemental Videos 2, 3, and 4. Abbreviations as in Figures 1, 2, and 3.