Babich L G, Fomin V P, Kosterin S A
Biokhimiia. 1990 Oct;55(10):1890-901.
The effect of the membrane potential (K(+)-valinomycin system) on the Mg2+, ATP-dependent transport of Ca2+ in inside-out vesicles of myometrium sarcolemma has been studied. The membrane potential was identified by using a cyanine potential-sensitive probe, diS-C3-(5). In the presence of valinomycin (5.10(-8) M) the inside-out directed K+ gradient (delta psi = -86 mV, with a negative charge inside) stimulated the initial rate of the energy-dependent accumulation of Ca2+ transfer whereas the oppositely directed K+ gradient (delta psi = +72 mV, with a positive charge inside) had no effect on this process. The K+ gradient was formed by isotonic substitution of K+ in intra- or extravesicular space for choline +. At the same time, in the absence of K+ gradient the Mg2+, ATP-dependent accumulation of Ca2+ in membrane vesicles did not depend on the chemical nature of the cations (K+ or choline+) used for isotonicity. The decrease of delta psi from 0 to -86 mV affects the initial rate of Ca2+ accumulation but not the maximal content of the accumulated cation. Preliminary dissipation of the membrane potential (delta psi = -86 mV) in Mg2(+)-free isotonic (with respect of K+ and choline+) media containing ATP and Ca2+ resulted in the inhibition of Mg2+, ATP-dependent Ca2+ transport induced by subsequent addition of Mg2+. These results indicate that the negative (intravesicular) electrical potential activates the Ca-pump of smooth muscle sarcolemma. This activation is based on the increase in the turnover number of the Ca2+ transporting system but not on its affinity for the transfer substrate. The use of the absolute reaction rates theory made it possible to establish that the Ca-pump effectuates the transport of a single positive charge in inside-out vesicles of smooth muscle plasma membranes, i.e., the energy-dependent transport of Ca2+ occurs either as a symport (with an anion (Cl-) or an antiport with a monovalent cation (K+) or a proton. It is assumed that the potential dependence of the Ca-pump in the smooth muscle plasma membrane plays a role in the realization of effects of mediators and physiologically active substances that are manifested as stimulation of the contractile response and depolarization of the sarcolemma. In is quite probable that the delta psi-dependent Ca-pump is also responsible for the maintenance of intracellular homeostasis of monovalent cations (K+, H+, Cl-) in smooth muscle tissues.
研究了膜电位（K⁺-缬氨霉素系统）对子宫肌层肌膜内翻小泡中Mg²⁺、ATP依赖的Ca²⁺转运的影响。通过使用一种花青电位敏感探针二硫代辛二酰三乙胺（diS-C3-(5)）来确定膜电位。在存在缬氨霉素（5×10⁻⁸ M）的情况下，内翻方向的K⁺梯度（Δψ = -86 mV，内部带负电荷）刺激了能量依赖的Ca²⁺转运的初始速率，而相反方向的K⁺梯度（Δψ = +72 mV，内部带正电荷）对该过程没有影响。K⁺梯度是通过在囊泡内或囊泡外空间用胆碱⁺等渗替代K⁺形成的。同时，在不存在K⁺梯度的情况下，膜小泡中Mg²⁺、ATP依赖的Ca²⁺积累不依赖于用于等渗的阳离子（K⁺或胆碱⁺）的化学性质。Δψ从0降低到 -86 mV会影响Ca²⁺积累的初始速率，但不影响积累阳离子的最大含量。在含有ATP和Ca²⁺的无Mg²⁺等渗（相对于K⁺和胆碱⁺）介质中预先消散膜电位（Δψ = -86 mV），会导致随后添加Mg²⁺诱导的Mg²⁺、ATP依赖的Ca²⁺转运受到抑制。这些结果表明，负（囊泡内）电势激活了平滑肌肌膜的Ca泵。这种激活是基于Ca²⁺转运系统周转数的增加，而不是基于其对转运底物的亲和力。使用绝对反应速率理论可以确定，Ca泵在平滑肌质膜的内翻小泡中实现单个正电荷的转运，即能量依赖的Ca²⁺转运要么作为同向转运（与阴离子（Cl⁻）），要么作为与单价阳离子（K⁺）或质子的反向转运发生。据推测，平滑肌质膜中Ca泵的电位依赖性在介导剂和生理活性物质的作用实现中起作用，这些作用表现为收缩反应的刺激和肌膜的去极化。很可能依赖于Δψ的Ca泵也负责维持平滑肌组织中单价阳离子（K⁺、H⁺、Cl⁻）的细胞内稳态。
