Ca2+-activated Cl- current from human bestrophin-4 in excised membrane patches.
Bestrophins are a newly discovered family of Cl(-) channels, some members of which are activated by intracellular Ca(2+). So far, all studies were carried out with whole-cell recordings from plasmid-transfected cultured cells, so it is unclear whether Ca(2+) activates bestrophin through a metabolic mechanism or in a more direct way. We report here experiments that addressed this question with excised, inside-out membrane patches. We chose human bestrophin-4 (hBest4) for heterologous expression because it gave particularly large Cl(-) currents when expressed, thus allowing detection even in excised membrane patches. hBest4 gave a negligible Cl(-) current in a Ca(2+)-free solution on the cytoplasmic (bath) side, but produced a Cl(-) current that was activated by Ca(2+) in a dose-dependent manner, with a K(1/2) of 230 nM. Thus, Ca(2+) appears to activate the bestrophin Cl(-) channel without going through a freely diffusible messenger or through protein phosphorylation. Because the activation and deactivation kinetics were very slow, however, we cannot exclude the involvement of a membrane-associated messenger.
Tsunenari
Takashi
T
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. tsune@jhmi.edu
Nathans
Jeremy
J
Yau
King-Wai
KW
D000818:Animals; D000075002:Bestrophins; D016466:CHO Cells; D002118:Calcium / Q000737:chemistry / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D018118:Chloride Channels / Q000502:physiology*; D006224:Cricetinae; D005136:Eye Proteins / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods*
C113133:BEST1 protein, human; D000075002:Bestrophins; D018118:Chloride Channels; D005136:Eye Proteins; D002118:Calcium