Modulation of hepatocellular swelling-activated K+ currents by phosphoinositide pathway-dependent protein kinase C.
K(+) channels participate in the regulatory volume decrease (RVD) accompanying hepatocellular nutrient uptake and bile formation. We recently identified KCNQ1 as a molecular candidate for a significant fraction of the hepatocellular swelling-activated K(+) current (I(KVol)). We have shown that the KCNQ1 inhibitor chromanol 293B significantly inhibited RVD-associated K(+) flux in isolated perfused rat liver and used patch-clamp techniques to define the signaling pathway linking swelling to I(KVol) activation. Patch-electrode dialysis of hepatocytes with solutions that maintain or increase phosphatidylinositol 4,5-bisphosphate (PIP(2)) increased I(KVol), whereas conditions that decrease cellular PIP(2) decreased I(KVol). GTP and AlF(4)(-) stimulated I(KVol) development, suggesting a role for G proteins and phospholipase C (PLC). Supporting this, the PLC blocker U-73122 decreased I(KVol) and inhibited the stimulatory response to PIP(2) or GTP. Protein kinase C (PKC) is involved, because K(+) current was enhanced by 1-oleoyl-2-acetyl-sn-glycerol and inhibited after chronic PKC stimulation with phorbol 12-myristate 13-acetate (PMA) or the PKC inhibitor GF 109203X. Both I(KVol) and the accompanying membrane capacitance increase were blocked by cytochalasin D or GF 109203X. Acute PMA did not eliminate the cytochalasin D inhibition, suggesting that PKC-mediated I(KVol) activation involves the cytoskeleton. Under isotonic conditions, a slowly developing K(+) current similar to I(KVol) was activated by PIP(2), lipid phosphatase inhibitors to counter PIP(2) depletion, a PLC-coupled alpha(1)-adrenoceptor agonist, or PKC activators and was depressed by PKC inhibition, suggesting that hypotonicity is one of a set of stimuli that can activate I(KVol) through a PIP(2)/PKC-dependent pathway. The results indicate that PIP(2) indirectly activates hepatocellular KCNQ1-like channels via cytoskeletal rearrangement involving PKC activation.
Lan
Wen-Zhi
WZ
Department of Medicine and Physiology, GI Diseases Research Unit, Queen's University, Kingston, Ontario, Canada.
Wang
Penny Y T
PY
Hill
Ceredwyn E
CE
D000818:Animals; D048429:Cell Size / Q000187:drug effects; D004963:Estrenes / Q000494:pharmacology; D005260:Female; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D051657:KCNQ1 Potassium Channel / Q000502:physiology*; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D009994:Osmolar Concentration; D010477:Perfusion; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology*; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D004963:Estrenes; D051657:KCNQ1 Potassium Channel; D019269:Phosphatidylinositol 4,5-Diphosphate; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D011493:Protein Kinase C