Molecular characterization of volume-sensitive SK(Ca) channels in human liver cell lines.
In human liver, Ca(2+)-dependent changes in membrane K(+) permeability play a central role in coordinating functional interactions between membrane transport, metabolism, and cell volume. On the basis of the observation that K(+) conductance is partially sensitive to the bee venom toxin apamin, we aimed to assess whether small-conductance Ca(2+)-sensitive K(+) (SK(Ca)) channels are expressed endogenously and contribute to volume-sensitive K(+) efflux and cell volume regulation. We isolated a full-length 2,140-bp cDNA (hSK2) highly homologous to rat brain rSK2 cDNA, including the putative apamin-sensitive pore domain, from a human liver cDNA library. Identical cDNAs were isolated from primary human hepatocytes, human HuH-7 hepatoma cells, and human Mz-ChA-1 cholangiocarcinoma cells. Transduction of Chinese hamster ovary cells with a recombinant adenovirus encoding the hSK2-green fluorescent protein fusion construct resulted in expression of functional apamin-sensitive K(+) channels. In Mz-ChA-1 cells, hypotonic (15% less sodium glutamate) exposure increased K(+) current density (1.9 +/- 0.2 to 37.5 +/- 7.1 pA/pF; P < 0.001). Apamin (10-100 nM) inhibited K(+) current activation and cell volume recovery from swelling. Apamin-sensitive SK(Ca) channels are functionally expressed in liver and biliary epithelia and likely contribute to volume-sensitive changes in membrane K(+) permeability. Accordingly, the hSK2 protein is a potential target for pharmacological modulation of liver transport and metabolism through effects on membrane K(+) permeability.
Roman
Richard
R
Department of Medicine, School of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
Feranchak
Andrew P
AP
Troetsch
Marlyn
M
Dunkelberg
Jeffrey C
JC
Kilic
Gordon
G
Schlenker
Thorsten
T
Schaack
Jerome
J
Fitz
J Gregory
JG
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D016466:CHO Cells; D006528:Carcinoma, Hepatocellular; D048429:Cell Size / Q000502:physiology; D018281:Cholangiocarcinoma; D006224:Cricetinae; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D015723:Gene Library; D022781:Hepatocytes / Q000166:cytology / Q000502:physiology*; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology; D008113:Liver Neoplasms; D008322:Mammals; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D014158:Transcription, Genetic / Q000502:physiology; D014407:Tumor Cells, Cultured; D014882:Water-Electrolyte Balance / Q000502:physiology*
D007038:Hypotonic Solutions; D024681:Potassium Channels, Calcium-Activated; D001030:Apamin; D011188:Potassium