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Despite the progress in studies of the properties and functions of low-threshold calcium channels (LTCCs) [1], the mechanisms of their selectivity and permeability remain unstudied in detail. We performed a comparative analysis of the selectivity of three cloned pore-forming LTCC subunits (α1G, α1H, and α1I) functionally expressed in Xenopus oocytes with respect to bivalent alkaline-earth metal cations (Ва 2+ , Са 2+ , and Sr 2+ ). The relative conductivities (G) of these channels were determined according to the amplitudes of macroscopic currents (I) and potentials of zero currents (E). The currents were recorded after preliminary intracellular injection of a fast calcium buffer, BАРТА, in order to suppress the endogenous calciumdependent chloride conductivity. Channels formed by α1G subunits demonstrated the following ratios of the amplitudes of macroscopic currents and potentials of zero current: I Ca :I Ba :I Sr = 1.00:0.75:1.12 and E Ca ≈ E Ba ≈ E Sr . For channels that were formed by α1H and α1I subunits, these ratios were as follows: I Ca :I Ba :I Sr = 1.00:1.20:1.17, E Ca ≈ E Ba ≈ E Sr and I Ca :I Ba :I Sr = 1.00:1.48:1.45, E Ca ≈ E Ba ≈ E Sr , respectively. The different macroscopic conductivities and similar potentials of zero current typical of α1G and α1І channels indicate that, probably, various bivalent cations can in a differential manner influence the stochastic parameters of functioning of these channels. At the same time, channels formed by α1Н subunits are characterized by more positive potentials of zero current for Са 2+ . It seems possible that the selectivity of the above channels is determined by mechanisms that mediate the selectivity of most high-threshold calcium channels (more affine binding of Са 2+ inside the pore).

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