Hui Kwokyin, Gardzinski Peter, Sun Hong-Shuo, Backx Peter H, Feng Zhong-Ping
Department of Physiology, University of Toronto, Toronto, Ont., Canada M5S 1A8.
Biochem Biophys Res Commun. 2005 Dec 16;338(2):783-92. doi: 10.1016/j.bbrc.2005.10.014. Epub 2005 Oct 13.
Although ion permeation and gating of L-type Ca(2+) channels are generally considered separate processes controlled by distinct components of the channel protein, ion selectivity can vary with the kinetic state. To test this possibility, we studied single-channel currents (cell-attached) of recombinant L-type channels (Ca(V)1.2, beta(2a), and alpha(2)delta) transiently expressed in tsA201 cells in the presence of the channel agonist BayK 8644 which promotes long channel openings (Mode 2 openings). We found that both the brief (Mode 1) and long (Mode 2) mean open times in the presence of Ca(2+) were relatively longer than those with Ba(2+). The unitary slope conductance with Ba(2+) was significantly larger (p<0.05) in Mode 2 openings than for brief Mode 1 openings, whereas the conductance with Ca(2+) did not vary with mode gating. Consequently, the gamma(Ba):gamma(Ca) ratio was greater for Mode 2 than Mode 1 openings. Our findings indicate that both ion permeation and gating kinetics of the L-type channel are differentially modulated by permeable ions. Ca(2+) binding to the L-type channel may stabilize the alteration of channel ion permeability mediated by gating kinetics, and thus, play a role in preventing excessive ion entry when the activation gating of the channel is promoted to the prolonged open state.
尽管一般认为L型Ca(2+)通道的离子通透和门控是由通道蛋白不同组分控制的独立过程，但离子选择性会随动力学状态而变化。为了验证这种可能性，我们研究了在通道激动剂BayK 8644存在的情况下，瞬时转染于tsA201细胞中的重组L型通道（Ca(V)1.2、β(2a)和α(2)δ）的单通道电流（细胞贴附式），BayK 8644可促进通道长时间开放（模式2开放）。我们发现，在Ca(2+)存在时，短暂（模式1）和长时间（模式2）的平均开放时间相较于Ba(2+)存在时都相对更长。在模式2开放中，Ba(2+)的单位斜率电导显著大于短暂的模式1开放（p<0.05），而Ca(2+)的电导则不随门控模式变化。因此，模式2的γ(Ba):γ(Ca)比值大于模式1开放。我们的研究结果表明，L型通道的离子通透和门控动力学均受到可通透离子的差异调节。Ca(2+)与L型通道结合可能稳定由门控动力学介导的通道离子通透性改变，从而在通道激活门控转变为延长开放状态时，在防止过量离子内流方面发挥作用。
