DiFrancesco D, Porciatti F, Cohen I S
Dipartimento di Fisiologia e Biochimica Generali, Milano, Italy.
Experientia. 1991 May 15;47(5):449-52. doi: 10.1007/BF01959940.
The isolation of ionic fluxes contributing to electric currents through cell membranes often requires block of other undesired components which can be achieved, among others, by divalent cations. Mn2+ and Ba2+ are often used, for example, to block Ca and K currents. Here we have investigated the effects of these two cations on the properties of the hyperpolarization-activated pacemaker current if, in rabbit sino-atrial node myocytes, as obtained by voltage clamp analysis. We find that 2 mM Mn2+ shifts the if activation curve by 3.2 +/- 0.3 mV towards more positive values. However, when 1 mM Ba2+ is also added, the positive shift is more than halved (1.3 +/- 0.2 mV). We find, too, that in the absence of blocking cations the ACh-induced if inhibition is slightly higher than in their presence. These results indicate that the alteration of if kinetic properties by Ba2+ plus Mn(2+)-containing solutions is minimal.
通过细胞膜分离对电流有贡献的离子流，通常需要阻断其他不想要的成分，这可以通过二价阳离子等实现。例如，Mn2+和Ba2+常被用于阻断Ca和K电流。在此，我们通过电压钳分析研究了这两种阳离子对兔窦房结心肌细胞中超极化激活起搏电流（If）特性的影响。我们发现，2 mM Mn2+使If激活曲线向更正电位方向移动3.2±0.3 mV。然而，当同时加入1 mM Ba2+时，正向移动幅度减半以上（1.3±0.2 mV）。我们还发现，在没有阻断阳离子的情况下，ACh诱导的If抑制比有阻断阳离子时略高。这些结果表明，含Ba2+加Mn2+的溶液对If动力学特性的改变最小。
