Abstract:
:In an open circuit there can be no net cation flux through membranes containing only cation-selective channels, because electroneutrality must be maintained. If the channels are so narrow that water and cations cannot pass by each other, then the net water flux through those "single-file" channels that contain a cation is zero. It is therefore possible to determine the cation binding constants from the decrease in the average water permeability per channel as the cation concentration in the solution is increased. Three different methods were used to determine the osmotic water permeability of gramicidin channels in lipid bilayer membranes. The osmotic water permeability coefficient per gramicidin channel in the absence of cations was found to be 6 x 10(-14) cm3/s. As the cation concentration was raised, the water permeability decreased and a binding constant was determined from a quantitative fit to the data. When the data were fitted assuming a maximum of one ion per channel, the dissociation constant was 115 mM for Li+, 69 mM for K+, and 2 mM for Tl+.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Dani JA,Levitt DGdoi
10.1016/S0006-3495(81)84804-7subject
Has Abstractpub_date
1981-08-01 00:00:00pages
485-99issue
2eissn
0006-3495issn
1542-0086pii
S0006-3495(81)84804-7journal_volume
35pub_type
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