[Application of a triple barrier model to describe the energy profile of a calcium channel in the neuronal membranes of mollusks].
On the basis of measurements of the current-voltage characteristic shifts in the neuronal membrane of Helix pomatia the density and binding constants are calculated for charged groups of its outer surface. The obtained values are: sigma = 0.23 e-/nm2, KCa = 70 M-1, K Sr = 40 M-1, KBa = 20 M-1. These data are used for determination of near-membrane concentration of the carrier ions in the extracellular solution and true location of the current-voltage characteristics of calcium channels relative to the potential axis. The energy profile of calcium channel is calculated using a three-barrier model. The values of dissociation constants for calcium and barium ions with an outer binding site are equal to 10 and 91 mmol/l, respectively. The pK titration value for this site is 5.8. A conclusion is made that the value of inward ion current is determined mainly by the interaction energy between the carrier ion and the outer binding site which contains, probably, only one carboxylic group. The suppression of this current occurs under such a value of intracellular calcium concentration, when the occupation number of the inner binding site is considerably less than unity, and may be associated with an indirect influence of these ions through the system of cyclic nucleotides.
D000818:Animals; D001464:Barium / Q000378:metabolism; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D006372:Helix, Snails / Q000502:physiology; D006859:Hydrogen / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*
D007473:Ion Channels; D001464:Barium; D006859:Hydrogen; D002118:Calcium
Primenenie trekhbar'ernoĭ modeli dlia opisaniia énergeticheskogo profilia kal'tsievogo kanala v membrane neĭronov molliuskov.