Expression and canalicular localization of two isoforms of the ClC-3 chloride channel from rat hepatocytes.
The molecular identities of functional chloride channels in hepatocytes are largely unknown. We examined the ClC-3 chloride channel in rat hepatocytes and found that mRNA for two different isoforms is present. A short form is identical to the previously reported sequence for rat ClC-3, and a long form contains a 176-bp insertion immediately upstream of the translation initiation site. This predicts a 58-amino acid NH(2) terminal insertion. Both long and short form mRNA was expressed in diverse tissues of the rat. Transient transfection of the long form in CHO-K1 cells resulted in currents with an I(-) > B(-) > Cl(-) selectivity sequence, outward rectification, and inactivation at positive voltages. Short form currents had identical ionic selectivity but displayed a more extreme outward rectification and showed no voltage-dependent inactivation. Immunofluorescence and immunoblots localized native ClC-3 preferentially but not exclusively to the canalicular membrane. We have therefore identified a new isoform of rat ClC-3 and shown that expression of both isoforms produces functional channels. In hepatocytes, ClC-3 is located in association with the canalicular membrane.
Shimada
K
K
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77555, USA.
Li
X
X
Xu
G
G
Nowak
D E
DE
Showalter
L A
LA
Weinman
S A
SA
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D018118:Chloride Channels / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D006224:Cricetinae; D004594:Electrophysiology; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000502:physiology; D015640:Ion Channel Gating / Q000502:physiology; D007536:Isomerism; D008099:Liver / Q000737:chemistry* / Q000166:cytology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D018118:Chloride Channels; C115376:ClC-3 channel; D008565:Membrane Proteins; D012333:RNA, Messenger