Abstract
We show theoretically that extending pore models to allow for fluctuations between configurations with different energy profiles results in the prediction of coupling between fluxes and forces of different species diffusing through singly occupied pores. Considering the case of a one-site, two-barrier pore capable of existing in two states, and using Eyring rate theory to describe the translocation of two permeant species, the flux of each is found to be linked to the driving force of the other via cross coefficients that are given as explicit functions of concentrations and potential, and that obey Onsager's relations when the system is near equilibrium. Conditions for the existence of coupling are that both states of the channel be permeable to both diffusing species and that the peaks of the two energy barrier shift by different amounts during the state transition of the pore. Some implications of this model on phenomena of biological interest are discussed briefly.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Ashcroft F. M., Stanfield P. R. The influence of the permeant ions thallous and potassium on inward rectification in frog skeletal muscle. J Physiol. 1983 Oct;343:407–428. doi: 10.1113/jphysiol.1983.sp014900. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hagiwara S., Miyazaki S., Krasne S., Ciani S. Anomalous permeabilities of the egg cell membrane of a starfish in K+-Tl+ mixtures. J Gen Physiol. 1977 Sep;70(3):269–281. doi: 10.1085/jgp.70.3.269. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hille B., Schwarz W. Potassium channels as multi-ion single-file pores. J Gen Physiol. 1978 Oct;72(4):409–442. doi: 10.1085/jgp.72.4.409. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Läuger P. Ion transport through pores: a rate-theory analysis. Biochim Biophys Acta. 1973 Jul 6;311(3):423–441. doi: 10.1016/0005-2736(73)90323-4. [DOI] [PubMed] [Google Scholar]
- Läuger P. Kinetic properties of ion carriers and channels. J Membr Biol. 1980 Dec 30;57(3):163–78(-RETURN-). doi: 10.1007/BF01869585. [DOI] [PubMed] [Google Scholar]
- Läuger P., Stephan W., Frehland E. Fluctuations of barrier structure in ionic channels. Biochim Biophys Acta. 1980 Oct 16;602(1):167–180. doi: 10.1016/0005-2736(80)90299-0. [DOI] [PubMed] [Google Scholar]
- Myers V. B., Haydon D. A. Ion transfer across lipid membranes in the presence of gramicidin A. II. The ion selectivity. Biochim Biophys Acta. 1972 Aug 9;274(2):313–322. doi: 10.1016/0005-2736(72)90179-4. [DOI] [PubMed] [Google Scholar]
- Neher E., Sandblom J., Eisenman G. Ionic selectivity, saturation, and block in gramicidin A channels. II. Saturation behavior of single channel conductances and evidence for the existence of multiple binding sites in the channel. J Membr Biol. 1978 Apr 26;40(2):97–116. doi: 10.1007/BF01871143. [DOI] [PubMed] [Google Scholar]
- Sandblom J., Eisenman G., Neher E. Ionic selectivity, saturation and block in gramicidin A channels: I. Theory for the electrical properties of ion selective channels having two pairs of binding sites and multiple conductance states. J Membr Biol. 1977 Mar 23;31(4):383–347. doi: 10.1007/BF01869414. [DOI] [PubMed] [Google Scholar]