Activation of protein kinase Cα couples cell volume to membrane Cl permeability in HTC hepatoma and Mz-ChA-1 cholangiocarcinoma cells

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Abstract

Physiological increases in liver cell volume lead to an adaptive response that includes opening of membrane Cl channels, which is critical for volume recovery. The purpose of these studies was to assess the potential role for protein kinase C (PKC) as a signal involved in cell volume homeostasis. Studies were performed in HTC rat hepatoma and Mz-ChA-1 human cholangiocarcinoma cells, which were used as model hepatocytes and cholangiocytes, respectively. In each cell type, cell volume increases were followed by: 1) translocation of PKCα from cytosolic to particulate (membrane) fractions; 2) a 10- to 40-fold increase in whole-cell membrane Cl current density; and 3) partial recovery of cell volume. In HTC cells, the volume-dependent Cl current response (−46 ± 5 pA/pF) was inhibited by down-regulation of PKC (100 nmol/L phorbol 12-myristate 13-acetate for 18 hours [PMA]; −1.97 ± 1.5 pA/pF), chelation of cytosolic Ca2+ (2 mmol/L EGTA; −5.3 ± 4.0 pA/pF), depletion of cytosolic adenosine triphosphate (ATP) (3 U/mL apyrase; −12.58 ± 1.45 pA/pF), and by the putative PKC inhibitor, chelerythrine (25 μmol/L; −7 ± 3 pA/pF). In addition, PKC inhibition by chelerythrine and calphostin C (500 nmol/L) prevented cell volume recovery from swelling. Similar results were obtained in Mz-ChA-1 biliary cells. These findings indicate that swelling-induced activation of PKC represents an important signal coupling cell volume to membrane Cl permeability in both hepatic and biliary cell models.

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