Differentiation of the transmembrane Na and Ca channels in mammalian cardiac fibres by the use of specific inhibitors
- Cite this article as:
- Kohlhardt, M., Bauer, B., Krause, H. et al. Pflugers Arch. (1972) 335: 309. doi:10.1007/BF00586221
Verapamil (2 mg/l) and compound D 600 (0.5 mg/l) produce a drastic reduction in the transmembrane Ca conductivity. The Ca current can be restored by increasing the extracellular Ca concentration.
In contrast to their strong inhibitory effects on the passive transmembrane Ca movements verapamil and D 600 in corresponding concentrations do not block the fast Na current.
Verapamil and D 600 differ in this respect from common local anesthetic compounds such as xylocaine (lidocaine) or procaine which interfere much more with the transmembrane Na conductivity than with the Ca conductivity.
The selective depression of the Ca or the Na conductivity by specific inhibitors indicates that during excitation the influxes of Na and Ca are independent of each other. Therefore, in the mammalian myocardium the existence of two separate channels for Na and Ca has to be assumed.
As a functional significance of this dual membrane transport system it is possible to change the contractile force by inotropic substances which act on the Ca conductivity without a corresponding influence on excitation.