Regulatory volume decrease (RVD) is crucial for cells to survive swelling. The volume sensitive outwardly rectifying anion channel (VSOR) is considered to be the major anion channel governing RVD in many tissues and cells. The cystic fibrosis transmembrane conductance regulator (CFTR) functions as both an intracellular ligand-gated channel and a regulator of other channels and transporters in many epithelial tissues. The loss of CFTR impaired RVD of epithelial cells with elusive mechanism. Our lab found that stretch activates CFTR and thus we hypothesize that CFTR may mediate epithelial RVD by directly responding to the mechanical stress induced by cell-swelling. Here we examined the molecular identity of volume-sensing anion channel in epithelia RVD by blocking VSOR and CFTR a...[ Read more ]

Regulatory volume decrease (RVD) is crucial for cells to survive swelling. The volume sensitive outwardly rectifying anion channel (VSOR) is considered to be the major anion channel governing RVD in many tissues and cells. The cystic fibrosis transmembrane conductance regulator (CFTR) functions as both an intracellular ligand-gated channel and a regulator of other channels and transporters in many epithelial tissues. The loss of CFTR impaired RVD of epithelial cells with elusive mechanism. Our lab found that stretch activates CFTR and thus we hypothesize that CFTR may mediate epithelial RVD by directly responding to the mechanical stress induced by cell-swelling. Here we examined the molecular identity of volume-sensing anion channel in epithelia RVD by blocking VSOR and CFTR activities. In Calu-3 cells, an airway epithelial cell-line with highly expressed CFTR, hypotonicity-induced short circuit current (I_sc) is sensitive to CFTR specific inhibitor but not to VSOR inhibitors. The l_sc was independent of cytoplasmic ca²⁺ levels and cAMP levels, suggesting the mechanosensitivity of CFTR played a role. Moreover, genetic suppression or ablation of CFTR markedly reduced swelling induced l_sc. In cultured CHO cells and freshly isolated intestinal crypts expressing CFTR, blocking CFTR abolished RVD triggered by hypotonicity. RVD is important in cell migration. We found that exogenous CFTR expression accelerated cell migration in HEK293T cells. Surprisingly, GSS1D, a CFTR mutation lacking cAMP-induced chloride channel activity, functioned like wild-type CFTR in swelling- or stretch-induced l_sc, RVD and cell migration. Furthermore, cell swelling also activated CFTR in cell-attached membrane patches in Calu-3 cells. Thus, our studies showed that both wild-type and G551D CFTR might be involved in epithelial RVD by responding to the mechanical stress induced by cell-swelling. Our findings also might explain the relative milder phenotype of cystic fibrosis (CF) patients carrying G551D mutation and shed light on developing novel mechanical treatment for CF.