ACTIVATION OF PROTEIN-KINASE-C-ALPHA COUPLES CELL-VOLUME TO MEMBRANE CL- PERMEABILITY IN HTC HEPATOMA AND MZ-CHA-1 CHOLANGIOCARCINOMA CELLS

Physiological increases in liver cell volume lead to an adaptive respo nse that includes opening of membrane Cl- channels, which is critical for volume recovery, The purpose of these studies was to assess the po tential role for protein kinase C (PKC) as a signal involved in cell v olume homeostasis. Studies were performed in HTC rat hepatoma and Mz-C hA-1 human cholangiocarcinoma cells, which were used as model hepatocy tes and cholangiocytes, respectively. In each cell type, cell volume i ncreases were followed by: 1) translocation of PKC alpha from cytosoli c to particulate (membrane) fractions; 2) a 10- to 40-fold increase in whole-cell membrane Cl- current density; and 3) partial recovery of c ell volume. In HTC cells, the volume-dependent Cl- current response (- 46 +/- 5 pA/pF) was inhibited by down-regulation of PKC (100 nmol/L ph orbol 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), dep letion of cytosolic adenosine triphosphate (ATP) (3 U/mL apyrase; -12. 58 +/- 1.45 pA/pF), and by the putative PKC inhibitor, chelerythrine ( 25 mu mol/L; -7 +/- 3 pA/pF), In addition, PKC inhibition by cheleryth rine and calphostin C (500 nmol/L) prevented cell volume recovery from swelling. Similar results were obtained in Mz-ChA-1 biliary cells. Th ese findings indicate that swelling-induced activation of PKC represen ts an important signal coupling cell volume to membrane Cl- permeabili ty in both hepatic and biliary cell models.