The Journal of General Physiology
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Published online 15 May 2006 doi:10.1085/jgp.200609527
The Rockefeller University Press, 0022-1295 $8.00
JGP, Volume 127, Number 6, 749-754
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 Ca2+-activated Cl– Current from Human Bestrophin-4 in Excised Membrane Patches



Takashi Tsunenari1, Jeremy Nathans1,2,3,4, and King-Wai Yau1,2

1 Department of Neuroscience, 2 Department of Ophthalmology, 3 Department of Molecular Biology and Genetics, and 4 Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205

Correspondence to T. Tsunenari: tsune{at}jhmi.edu

Bestrophins are a newly discovered family of Cl– channels, some members of which are activated by intracellular Ca2+. So far, all studies were carried out with whole-cell recordings from plasmid-transfected cultured cells, so it is unclear whether Ca2+ 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 Ca2+-free solution on the cytoplasmic (bath) side, but produced a Cl– current that was activated by Ca2+ in a dose-dependent manner, with a K1/2 of 230 nM. Thus, Ca2+ 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.

Abbreviations used in this paper: hBest, human bestrophin; mBest, mouse bestrophin; xBest, Xenopus bestrophin; RPE, retinal pigment epithelial.


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