Richard S, Potreau D, Charnet P, Raymond G, Nargeot J
Laboratoire d'Electrophysiologie et Pharmacologie Cellulaires, C.R.B.M., C.N.R.S. UPR.41, INSERM U. 249, Montpellier, France.
J Mol Cell Cardiol. 1989 Sep;21(9):865-75. doi: 10.1016/0022-2828(89)90755-4.
Ba2+ and Sr2+ ions are widely used to replace Ca2+ ions for the study of Ca2+ channel currents in electrophysiological experiments. Using the double sucrose gap technique, we investigated the effects of Sr2+ and Ba2+ ions on the Na+ Ca2+ exchange activity in frog atrial fibres where it is the major relaxation mechanism. With either Sr2+ or Ba2+ ions instead of Ca2+ in the extracellular bath, Na-free contractures reversibly developed but with different kinetics. Voltage clamp experiments showed that the tonic tension recorded in the presence of Sr2+ or Ba2+ was markedly increased following the addition of monensin, a Na+ ionophore known to increase the intracellular Na+ activity. In Na-free solutions (Li-substituted), it was possible to induce contractures by substituting Sr2+ or Ba2+ ions for extracellular Ca2+. These contractures could be relaxed by reintroducing Na+ or Ca2+ ions in the extracellular medium. Taken together, these results suggest that Sr2+ and Ba2+ ions can interact with the Na+-Ca2+ exchange mechanism and potentially participate not only in Na+-cation but also in Ca2+-cation exchanges on either side of the sarcolemmal membrane.
在电生理实验中，Ba2+和Sr2+离子被广泛用于替代Ca2+离子，以研究Ca2+通道电流。我们采用双蔗糖间隙技术，研究了Sr2+和Ba2+离子对蛙心房纤维中Na+-Ca2+交换活性的影响，在蛙心房纤维中，Na+-Ca2+交换是主要的舒张机制。当细胞外浴液中用Sr2+或Ba2+离子替代Ca2+时，无钠挛缩可逆地发展，但动力学不同。电压钳实验表明，在加入莫能菌素（一种已知可增加细胞内Na+活性的Na+离子载体）后，在Sr2+或Ba2+存在下记录的强直张力显著增加。在无钠溶液（Li替代）中，用Sr2+或Ba2+离子替代细胞外Ca2+可诱导挛缩。通过在细胞外介质中重新引入Na+或Ca2+离子，这些挛缩可以缓解。综上所述，这些结果表明，Sr2+和Ba2+离子可以与Na+-Ca2+交换机制相互作用，不仅可能参与肌膜两侧的Na+-阳离子交换，还可能参与Ca2+-阳离子交换。
