Acid induces TRPV4‐mediated calcium influx in mouse esophageal keratinocytes

Abstract

Exposure of the inner esophageal epithelial layer to an acidic environment has long been held as a major component of gastroesophageal reflux disease. The study aimed to determine if TRPV4, a Ca2+‐permeable channel, and Ca2+ signaling may play a role in acid sensing as part of this process. Primary culture mouse esophageal keratinocytes were grown to confluency on coverslips and intracellular Ca2+, [Ca2+]i, monitored with the fluorescent indicator, Fura 2‐AM, via microscopic imaging. In control WT cells, addition of GSK1016 790A (30 nM), a selective TRPV4 agonist, or exposure of cells to hypotonic media, a stimulus known to activate TRPV4, induce a rapid elevation in [Ca2+]i. These responses were abolished in cells cultured from TRPV4 knockout mice, thereby demonstrating functional TRPV4 channels in the keratinocytes. In separate studies, cells exposed to low pH media showed little or no [Ca2+]i response to pH 6 media, a modest response to pH 5 media, and a strong response to pH 4 media. However, in cells cultured from TRPV4 knockout mice, the response to all pH states was largely abolished. We conclude that espophageal keratinocytes express TRPV4 and that this channel is activated by acidic pH (pH 4 – 5) and, thus, may be part of the mechanism underlining gastroesophageal reflux disease.