Kostiuk P G, Mironov S L, Doroshenko P A
Neirofiziologiia. 1981;13(3):322-31.
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.
基于对苹果螺神经元膜电流 - 电压特性偏移的测量，计算出其外表面带电基团的密度和结合常数。得到的值为：σ = 0.23 e⁻/nm²，KCa = 70 M⁻¹，KSr = 40 M⁻¹，KBa = 20 M⁻¹。这些数据用于确定细胞外溶液中载体离子的近膜浓度以及钙通道电流 - 电压特性相对于电位轴的真实位置。使用三势垒模型计算钙通道的能量分布。钙和钡离子与外结合位点的解离常数分别为10和91 mmol/L。该位点的pK滴定值为5.8。得出的结论是，内向离子电流的值主要由载体离子与外结合位点之间的相互作用能决定，该外结合位点可能仅包含一个羧基。当细胞内钙浓度达到这样的值时，内向离子电流受到抑制，此时内结合位点的占据数远小于1，并且可能与这些离子通过环核苷酸系统的间接影响有关。
