Linked Life Data

7539500

Source:http://linkedlifedata.com/resource/pubmed/id/7539500

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
3
pubmed:dateCreated
1995-7-6
pubmed:abstractText
Gramicidin A pores are permeable to water and small monovalent cations. For K, Rb, and Cs there is good evidence from conductances and permeability ratios that a second ion can enter a pore already occupied by another, but for Na this evidence is inconclusive and comparison of tracer fluxes and single channel conductances suggests that second ion entries are prohibited. Partly as a result of the complications of second ion entry there have been widely differing estimates for the dissociation constants for the first ion in the channel. Dani and Levitt (1981, Biophys. J. 35: 485-499) introduced a method for calculating ion binding constants from simultaneous measurements of water fluxes and membrane conductance. They found no evidence for second ion binding and calculated dissociation constants of 115 mM for Li, 69 mM for K, and 2 mM for Tl. It is shown here that the two-ion, four-state model predicts a dependence of water permeability on ion concentration that is difficult to distinguish from the predictions of block by a single ion. Using a modified technique that allows measurement of higher conductances, the first ion dissociation constants have been determined as 80 mM for Na, 40 mM for Rb and 15 mM for Cs. These values and those of Dani and Levitt fall in a smooth sequence. The dissociation constant for Cs is consistent with single channel conductances and flux ratios. There is a discrepancy between this constant for Na and the value, 370 mM, calculated from the single channel conductances and the assumption that a second ion cannot enter or affect an occupied pore. The dissociation constant for Rb is intermediate between those for K and Cs whereas tracer flux measurements (Schagina, Grinfeldt & Lev, 1983. J. Membrane Biol. 73: 203-216) have suggested that Rb interacts much more strongly with the channel than Cs.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Feb
pubmed:issn
0022-2631
pubmed:author
pubmed:issnType
Print
pubmed:volume
143
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
247-57
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1995
pubmed:articleTitle
Ion binding constants for gramicidin A obtained from water permeability measurements.
pubmed:affiliation
Department of Pharmacology, University of Cambridge, United Kingdom.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't