Is the C-terminal arm of lens gap junction channel protein the channel gate?
Lens gap junction channels are studied in a reconstituted system obtained by incorporating into liposomes, with or without calmodulin, the lens junction protein (MIP26) and its trypsin-cleaved product (MIP21) that lacks the C-terminal arm. Channel permeability is studied with an osmotic swelling assay. MIP26 and MIP21 liposomes swell in sucrose or polyethyleneglycol with or without Ca++ indicating the presence of large channels. Without Ca++, MIP26 and MIP21 liposomes swell in both permeants. With Ca++, MIP26-calmodulin liposomes do not swell in either permeant, indicating complete channel closure, while MIP21-calmodulin liposomes swell in sucrose but not in polyethyleneglycol. This suggests that the C-terminal arm participates in channel gating.
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D000818:Animals; D020346:Aquaporins; D002118:Calcium / Q000502:physiology; D002147:Calmodulin / Q000502:physiology; D002417:Cattle; D002463:Cell Membrane Permeability; D017630:Connexins; D005136:Eye Proteins / Q000502:physiology*; D005614:Freeze Fracturing; D007473:Ion Channels / Q000378:metabolism*; D007908:Lens, Crystalline / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000502:physiology*; D008854:Microscopy, Electron; D009997:Osmotic Pressure; D010446:Peptide Fragments / Q000502:physiology; D011092:Polyethylene Glycols; D013395:Sucrose
D020346:Aquaporins; D002147:Calmodulin; D017630:Connexins; D005136:Eye Proteins; D007473:Ion Channels; D008081:Liposomes; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010446:Peptide Fragments; C030328:aquaporin 0; C046263:lens intrinsic protein MIP 21; D011092:Polyethylene Glycols; D013395:Sucrose; D002118:Calcium