Calcium mobilization evoked by hepatocellular swelling is linked to activation of phospholipase Cgamma.
Recovery from swelling of hepatocytes and selected other epithelia is triggered by intracellular Ca(2+) release from the endoplasmic reticulum, which leads to fluid and electrolyte efflux through volume-sensitive K(+) and Cl(-) channels. The aim of this study was to determine the mechanisms responsible for swelling-mediated hepatocellular Ca(2+) mobilization. Swelling of HTC rat hepatoma cells, evoked by exposure to hypotonic medium, elicited transient increases in intracellular levels of inositol 1,4,5-trisphosphate (IP(3)) and cytosolic [Ca(2+)]. The latter was attenuated by inhibition of phospholipase C (PLC) with and by IP(3) receptor blockade with 2-aminoethoxydiphenyl borate, but it was unaffected by ryanodine, an inhibitor of intracellular Ca(2+)-induced Ca(2+) release channels. Hypotonic swelling was associated with a transient increase in tyrosine phosphorylation of PLCgamma, with kinetics that paralleled the increases in intracellular IP(3) levels and cytosolic [Ca(2+)]. Confocal imaging of HTC cells exposed to hypotonic medium revealed a swelling-induced association of tyrosine-phosphorylated PLCgamma with the plasma membrane. These findings suggest that activation of PLCgamma by hepatocellular swelling leads to the generation of IP(3) and stimulates discharge of Ca(2+) from the endoplasmic reticulum via activation of IP(3) receptors. By extension, these data support the concept that tyrosine phosphorylation of PLCgamma represents a critical step in adaptive responses to hepatocellular swelling.
Moore
Ann L
AL
Department of Medicine, University of Vermont College of Medicine, Burlington, VT 05401, USA.
Roe
Michael W
MW
Melnick
Richard F
RF
Lidofsky
Steven D
SD
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D048429:Cell Size / Q000502:physiology*; D004789:Enzyme Activation; D004963:Estrenes / Q000494:pharmacology; D022781:Hepatocytes / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes / Q000378:metabolism*; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism*
D015220:Calcium Channels; D004963:Estrenes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes; D011760:Pyrrolidinones; D018160:Receptors, Cytoplasmic and Nuclear; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium