K2P2.1 channels modulate the pH- and mechanosensitivity of pancreatic stellate cells.

Abstract

Pancreatic stellate cells (PSCs) are central in the development of acute pancreatitis and tumor fibrosis in pancreatic ductal adenocarcinoma (PDAC). Fibrosis and a unique pH landscape represent characteristic properties of the PDAC microenvironment. Mechanosensitive ion channels are involved in the activation of PSCs. Among these channels, K_2P2.1 has not yet been studied in PSCs. K_2P2.1 channels are pH- and mechanosensitive. We confirmed K_2P2.1 expression in PSCs by RT-qPCR and immunofluorescence. PSCs from K_2P2.1^+/+ and K_2P2.1^-/- mice were studied under conditions mimicking properties of the PDAC microenvironment (acidic extracellular pH (pH_e), ambient pressure elevated by + 100 mmHg). Migration and the cell area were taken as surrogates for PSC activation and evaluated with live cell imaging. pH_e-dependent changes of the membrane potential of PSCs were investigated with DiBAC₄(3), a voltage-sensitive fluorescent dye. We observed a correlation between morphological activation and progressive hyperpolarization of the cells in response to changes in pH_e and pressure. The effect was in part dependent on the expression of K_2P2.1 channels because the membrane potential of K_2P2.1^+/+ PSCs was always more hyperpolarized than that of K_2P2.1^-/- PSCs. Cell migration velocity of K_2P2.1^+/+ cells decreased upon pressure application when cells were kept in an acidic medium (pH_e 6.6). This was not the case in K_2P2.1^-/- PSCs. Taken together, our study highlights the critical role of K_2P2.1 channels in the combined sensing of environmental pressure and pH_e by PSCs and in coordinating cellular morphology with membrane potential dynamics. Thus, K_2P2.1 channels are important mechano-sensors in murine PSCs.